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  Subjects -> CHEMISTRY (Total: 852 journals)
    - ANALYTICAL CHEMISTRY (52 journals)
    - CHEMISTRY (598 journals)
    - CRYSTALLOGRAPHY (21 journals)
    - ELECTROCHEMISTRY (25 journals)
    - INORGANIC CHEMISTRY (41 journals)
    - ORGANIC CHEMISTRY (46 journals)
    - PHYSICAL CHEMISTRY (69 journals)

CHEMISTRY (598 journals)                  1 2 3 | Last

Showing 1 - 200 of 735 Journals sorted alphabetically
2D Materials     Hybrid Journal   (Followers: 10)
Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement     Hybrid Journal   (Followers: 26)
ACS Catalysis     Full-text available via subscription   (Followers: 38)
ACS Chemical Neuroscience     Full-text available via subscription   (Followers: 18)
ACS Combinatorial Science     Full-text available via subscription   (Followers: 23)
ACS Macro Letters     Full-text available via subscription   (Followers: 24)
ACS Medicinal Chemistry Letters     Full-text available via subscription   (Followers: 39)
ACS Nano     Full-text available via subscription   (Followers: 251)
ACS Photonics     Full-text available via subscription   (Followers: 12)
ACS Synthetic Biology     Full-text available via subscription   (Followers: 23)
Acta Chemica Iasi     Open Access   (Followers: 2)
Acta Chimica Sinica     Full-text available via subscription   (Followers: 1)
Acta Chimica Slovaca     Open Access   (Followers: 1)
Acta Chimica Slovenica     Open Access  
Acta Chromatographica     Full-text available via subscription   (Followers: 9)
Acta Facultatis Medicae Naissensis     Open Access  
Acta Metallurgica Sinica (English Letters)     Hybrid Journal   (Followers: 5)
Acta Scientifica Naturalis     Open Access   (Followers: 2)
adhäsion KLEBEN & DICHTEN     Hybrid Journal   (Followers: 5)
Adhesion Adhesives & Sealants     Hybrid Journal   (Followers: 8)
Adsorption Science & Technology     Full-text available via subscription   (Followers: 5)
Advanced Functional Materials     Hybrid Journal   (Followers: 51)
Advanced Science Focus     Free   (Followers: 3)
Advances in Chemical Engineering and Science     Open Access   (Followers: 57)
Advances in Chemical Science     Open Access   (Followers: 13)
Advances in Chemistry     Open Access   (Followers: 15)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 18)
Advances in Drug Research     Full-text available via subscription   (Followers: 22)
Advances in Enzyme Research     Open Access   (Followers: 9)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 8)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 16)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 9)
Advances in Materials Physics and Chemistry     Open Access   (Followers: 21)
Advances in Nanoparticles     Open Access   (Followers: 15)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 15)
Advances in Polymer Science     Hybrid Journal   (Followers: 41)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Science and Technology     Full-text available via subscription   (Followers: 12)
African Journal of Bacteriology Research     Open Access  
African Journal of Chemical Education     Open Access   (Followers: 2)
African Journal of Pure and Applied Chemistry     Open Access   (Followers: 7)
Agrokémia és Talajtan     Full-text available via subscription   (Followers: 2)
Al-Kimia : Jurnal Penelitian Sains Kimia     Open Access  
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 3)
AMB Express     Open Access   (Followers: 1)
Ambix     Hybrid Journal   (Followers: 3)
American Journal of Biochemistry and Biotechnology     Open Access   (Followers: 66)
American Journal of Biochemistry and Molecular Biology     Open Access   (Followers: 15)
American Journal of Chemistry     Open Access   (Followers: 27)
American Journal of Plant Physiology     Open Access   (Followers: 14)
American Mineralogist     Hybrid Journal   (Followers: 14)
Analyst     Full-text available via subscription   (Followers: 39)
Angewandte Chemie     Hybrid Journal   (Followers: 179)
Angewandte Chemie International Edition     Hybrid Journal   (Followers: 229)
Annales UMCS, Chemia     Open Access   (Followers: 1)
Annals of Clinical Chemistry and Laboratory Medicine     Open Access   (Followers: 4)
Annual Reports in Computational Chemistry     Full-text available via subscription   (Followers: 3)
Annual Reports Section A (Inorganic Chemistry)     Full-text available via subscription   (Followers: 4)
Annual Reports Section B (Organic Chemistry)     Full-text available via subscription   (Followers: 8)
Annual Review of Chemical and Biomolecular Engineering     Full-text available via subscription   (Followers: 12)
Annual Review of Food Science and Technology     Full-text available via subscription   (Followers: 16)
Anti-Infective Agents     Hybrid Journal   (Followers: 3)
Antiviral Chemistry and Chemotherapy     Hybrid Journal   (Followers: 1)
Applied Organometallic Chemistry     Hybrid Journal   (Followers: 7)
Applied Spectroscopy     Full-text available via subscription   (Followers: 22)
Applied Surface Science     Hybrid Journal   (Followers: 28)
Arabian Journal of Chemistry     Open Access   (Followers: 6)
ARKIVOC     Open Access   (Followers: 2)
Asian Journal of Biochemistry     Open Access   (Followers: 1)
Atomization and Sprays     Full-text available via subscription   (Followers: 4)
Australian Journal of Chemistry     Hybrid Journal   (Followers: 7)
Autophagy     Hybrid Journal   (Followers: 2)
Avances en Quimica     Open Access   (Followers: 1)
Biochemical Pharmacology     Hybrid Journal   (Followers: 10)
Biochemistry     Full-text available via subscription   (Followers: 324)
Biochemistry Insights     Open Access   (Followers: 6)
Biochemistry Research International     Open Access   (Followers: 6)
BioChip Journal     Hybrid Journal  
Bioinorganic Chemistry and Applications     Open Access   (Followers: 9)
Bioinspired Materials     Open Access   (Followers: 5)
Biointerface Research in Applied Chemistry     Open Access   (Followers: 2)
Biointerphases     Open Access   (Followers: 1)
Biology, Medicine, & Natural Product Chemistry     Open Access   (Followers: 1)
Biomacromolecules     Full-text available via subscription   (Followers: 19)
Biomass Conversion and Biorefinery     Partially Free   (Followers: 10)
Biomedical Chromatography     Hybrid Journal   (Followers: 6)
Biomolecular NMR Assignments     Hybrid Journal   (Followers: 3)
BioNanoScience     Partially Free   (Followers: 5)
Bioorganic & Medicinal Chemistry     Hybrid Journal   (Followers: 120)
Bioorganic & Medicinal Chemistry Letters     Hybrid Journal   (Followers: 84)
Bioorganic Chemistry     Hybrid Journal   (Followers: 10)
Biopolymers     Hybrid Journal   (Followers: 18)
Biosensors     Open Access   (Followers: 2)
Biotechnic and Histochemistry     Hybrid Journal   (Followers: 1)
Bitácora Digital     Open Access  
Boletin de la Sociedad Chilena de Quimica     Open Access  
Bulletin of the Chemical Society of Ethiopia     Open Access   (Followers: 2)
Bulletin of the Chemical Society of Japan     Full-text available via subscription   (Followers: 24)
Bulletin of the Korean Chemical Society     Hybrid Journal   (Followers: 1)
C - Journal of Carbon Research     Open Access   (Followers: 3)
Cakra Kimia (Indonesian E-Journal of Applied Chemistry)     Open Access  
Canadian Association of Radiologists Journal     Full-text available via subscription   (Followers: 3)
Canadian Journal of Chemistry     Hybrid Journal   (Followers: 10)
Canadian Mineralogist     Full-text available via subscription   (Followers: 5)
Carbohydrate Research     Hybrid Journal   (Followers: 26)
Carbon     Hybrid Journal   (Followers: 68)
Catalysis for Sustainable Energy     Open Access   (Followers: 7)
Catalysis Reviews: Science and Engineering     Hybrid Journal   (Followers: 8)
Catalysis Science and Technology     Free   (Followers: 7)
Catalysis Surveys from Asia     Hybrid Journal   (Followers: 3)
Catalysts     Open Access   (Followers: 8)
Cellulose     Hybrid Journal   (Followers: 7)
Cereal Chemistry     Full-text available via subscription   (Followers: 5)
ChemBioEng Reviews     Full-text available via subscription   (Followers: 1)
ChemCatChem     Hybrid Journal   (Followers: 8)
Chemical and Engineering News     Free   (Followers: 15)
Chemical Bulletin of Kazakh National University     Open Access  
Chemical Communications     Full-text available via subscription   (Followers: 70)
Chemical Engineering Research and Design     Hybrid Journal   (Followers: 25)
Chemical Research in Chinese Universities     Hybrid Journal   (Followers: 3)
Chemical Research in Toxicology     Full-text available via subscription   (Followers: 21)
Chemical Reviews     Full-text available via subscription   (Followers: 183)
Chemical Science     Open Access   (Followers: 22)
Chemical Technology     Open Access   (Followers: 16)
Chemical Vapor Deposition     Hybrid Journal   (Followers: 5)
Chemical Week     Full-text available via subscription   (Followers: 8)
Chemie in Unserer Zeit     Hybrid Journal   (Followers: 56)
Chemie-Ingenieur-Technik (Cit)     Hybrid Journal   (Followers: 24)
ChemInform     Hybrid Journal   (Followers: 8)
Chemistry & Biodiversity     Hybrid Journal   (Followers: 6)
Chemistry & Biology     Full-text available via subscription   (Followers: 30)
Chemistry & Industry     Hybrid Journal   (Followers: 5)
Chemistry - A European Journal     Hybrid Journal   (Followers: 149)
Chemistry - An Asian Journal     Hybrid Journal   (Followers: 15)
Chemistry and Materials Research     Open Access   (Followers: 20)
Chemistry Central Journal     Open Access   (Followers: 4)
Chemistry Education Research and Practice     Free   (Followers: 5)
Chemistry in Education     Open Access   (Followers: 9)
Chemistry International     Hybrid Journal   (Followers: 2)
Chemistry Letters     Full-text available via subscription   (Followers: 42)
Chemistry of Materials     Full-text available via subscription   (Followers: 248)
Chemistry of Natural Compounds     Hybrid Journal   (Followers: 9)
Chemistry World     Full-text available via subscription   (Followers: 22)
Chemistry-Didactics-Ecology-Metrology     Open Access   (Followers: 1)
ChemistryOpen     Open Access   (Followers: 2)
Chemkon - Chemie Konkret, Forum Fuer Unterricht Und Didaktik     Hybrid Journal  
Chemoecology     Hybrid Journal   (Followers: 4)
Chemometrics and Intelligent Laboratory Systems     Hybrid Journal   (Followers: 14)
Chemosensors     Open Access  
ChemPhysChem     Hybrid Journal   (Followers: 10)
ChemPlusChem     Hybrid Journal   (Followers: 2)
ChemTexts     Hybrid Journal  
CHIMIA International Journal for Chemistry     Full-text available via subscription   (Followers: 2)
Chinese Journal of Chemistry     Hybrid Journal   (Followers: 6)
Chinese Journal of Polymer Science     Hybrid Journal   (Followers: 10)
Chromatographia     Hybrid Journal   (Followers: 24)
Clay Minerals     Full-text available via subscription   (Followers: 10)
Cogent Chemistry     Open Access  
Colloid and Interface Science Communications     Open Access  
Colloid and Polymer Science     Hybrid Journal   (Followers: 10)
Colloids and Surfaces B: Biointerfaces     Hybrid Journal   (Followers: 6)
Combinatorial Chemistry & High Throughput Screening     Hybrid Journal   (Followers: 4)
Combustion Science and Technology     Hybrid Journal   (Followers: 19)
Comments on Inorganic Chemistry: A Journal of Critical Discussion of the Current Literature     Hybrid Journal   (Followers: 2)
Composite Interfaces     Hybrid Journal   (Followers: 6)
Comprehensive Chemical Kinetics     Full-text available via subscription   (Followers: 2)
Comptes Rendus Chimie     Full-text available via subscription  
Comptes Rendus Physique     Full-text available via subscription   (Followers: 1)
Computational and Theoretical Chemistry     Hybrid Journal   (Followers: 9)
Computational Biology and Chemistry     Hybrid Journal   (Followers: 11)
Computational Chemistry     Open Access   (Followers: 2)
Computers & Chemical Engineering     Hybrid Journal   (Followers: 9)
Coordination Chemistry Reviews     Full-text available via subscription   (Followers: 3)
Copernican Letters     Open Access   (Followers: 1)
Corrosion Series     Full-text available via subscription   (Followers: 6)
Critical Reviews in Biochemistry and Molecular Biology     Hybrid Journal   (Followers: 5)
Croatica Chemica Acta     Open Access  
Crystal Structure Theory and Applications     Open Access   (Followers: 4)
CrystEngComm     Full-text available via subscription   (Followers: 13)
Current Catalysis     Hybrid Journal   (Followers: 2)
Current Metabolomics     Hybrid Journal   (Followers: 5)
Current Opinion in Colloid & Interface Science     Hybrid Journal   (Followers: 9)
Current Opinion in Molecular Therapeutics     Full-text available via subscription   (Followers: 18)
Current Research in Chemistry     Open Access   (Followers: 8)
Current Science     Open Access   (Followers: 64)
Dalton Transactions     Full-text available via subscription   (Followers: 23)
Detection     Open Access   (Followers: 2)
Developments in Geochemistry     Full-text available via subscription   (Followers: 2)
Diamond and Related Materials     Hybrid Journal   (Followers: 12)
Dislocations in Solids     Full-text available via subscription  
Doklady Chemistry     Hybrid Journal  
Drying Technology: An International Journal     Hybrid Journal   (Followers: 4)
Eclética Química     Open Access   (Followers: 1)
Ecological Chemistry and Engineering S     Open Access   (Followers: 3)
Ecotoxicology and Environmental Contamination     Open Access  
Educación Química     Open Access   (Followers: 1)
Education for Chemical Engineers     Hybrid Journal   (Followers: 5)
EJNMMI Radiopharmacy and Chemistry     Open Access  

        1 2 3 | Last

Journal Cover ChemCatChem
  [SJR: 1.824]   [H-I: 56]   [8 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1867-3880 - ISSN (Online) 1867-3899
   Published by John Wiley and Sons Homepage  [1589 journals]
  • Engineered sulphur resistant catalyst system with an assisted regeneration
           strategy for lean-burn methane combustion
    • Authors: Niko M Kinnunen; Matthew Keenan, Kauko Kallinen, Teuvo Maunula, Mika Suvanto
      Abstract: Catalytic combustion of methane, the main component of natural gas, is a challenge under lean-burn conditions and at low temperature, due sulphur poisoning of the Pd rich catalyst. The paper introduces a more sulphur resistant catalyst system which can be regenerated in operation. The developed catalyst system lowers the barrier that has restrained the use of liquefied natural gas as a fuel in energy production.
      PubDate: 2018-01-12T03:20:44.487514-05:
      DOI: 10.1002/cctc.201701884
       
  • Controllable Synthesis of CoS2@N/S-Codoped Porous Carbon Derived from
           ZIF-67 for as a Highly Efficient Catalyst for the Hydrogen Evolution
           Reaction
    • Authors: Shi Feng; Xingyue Li, Jia Huo, Qiling Li, Chao Xie, Tingting Liu, Zhigang Liu, Zhenjun Wu, Shuangyin Wang
      Abstract: A convenient, controllable method to fabricate an electrode is necessary to achieve the practical application of a hydrogen evolution reaction (HER) catalyst. In this work, an electrodeposition–ZIF conversion–sulfuration strategy is developed to produce a CoS2@N/S-codoped porous carbon (CoS2@NSC/CFP) to drive the HER efficiently. CoS2@NSC/CFP was prepared by the electrodeposition of Co(OH)2 on a carbon fiber paper followed by conversion into ZIF-67 and subsequent sulfuration with sulfur. The loading of electroactive components can be controlled easily in the range of 0.7–10.0 mg cm−2 by varying electrodeposition time from 5 min to 2 h. The resulting material can be employed directly as a working electrode for the HER and it shows an excellent catalytic activity and stability with an overpotential of 95 mV at 10 mA cm−2 and 158 mV to reach 100 mA cm−2 in an acidic medium. The high efficiency is related intimately to the high dispersion of ultra-small CoS2 nanoparticles, heteroatom-codoping, and the 3 D porous network configuration of the carbon fiber paper.Porous carbon electrode: CoS2@N/S-codoped porous carbon is prepared through an electrodeposition–ZIF conversion–sulfuration strategy. The loading of active sites can be controlled easily by varying the electrodeposition time. The resulting material can be employed directly as a working electrode for the hydrogen evolution reaction and shows an excellent catalytic activity and stability.
      PubDate: 2018-01-11T09:07:19.256985-05:
      DOI: 10.1002/cctc.201701353
       
  • Hydrogen-Borrowing Alcohol Bioamination with Coimmobilized Dehydrogenases
    • Authors: Wesley Böhmer; Tanja Knaus, Francesco G. Mutti
      Abstract: The amination of alcohols is an important transformation in chemistry. The redox-neutral (i.e., hydrogen-borrowing) asymmetric amination of alcohols is enabled by the combination of an alcohol dehydrogenase (ADH) with an amine dehydrogenase (AmDH). In this work, we enhanced the efficiency of hydrogen-borrowing biocatalytic amination by co-immobilizing both dehydrogenases on controlled porosity glass FeIII ion-affinity beads. The recyclability of the dual-enzyme system was demonstrated (5 cycles) with total turnover numbers of>4000 and>1000 for ADH and AmDH, respectively. A set of (S)-configured alcohol substrates was aminated with up to 95 % conversion and>99 % ee (R). Preparative-scale amination of (S)-phenylpropan-2-ol resulted in 90 % conversion and 80 % yield of the product in 24 h.Something borrowed: We co-immobilize an alcohol dehydrogenase (ADH) and an amine dehydrogenase (AmDH) on controlled porosity glass FeIII affinity beads to perform the hydrogen-borrowing amination of (S)-configured alcohols with up to 95 % conversion,>99 % ee. Recyclability of the dual-enzyme system is demonstrated, whereas the total turnover numbers are>4000 and>1000 for ADH and AmDH, respectively.
      PubDate: 2018-01-11T09:07:09.049556-05:
      DOI: 10.1002/cctc.201701366
       
  • Identification of Novel Bacterial Members of the Imine Reductase Enzyme
           Family that Perform Reductive Amination
    • Authors: Scott P. France; Roger M. Howard, Jeremy Steflik, Nicholas J. Weise, Juan Mangas-Sanchez, Sarah L. Montgomery, Robert Crook, Rajesh Kumar, Nicholas J. Turner
      Abstract: Reductive amination of carbonyl compounds constitutes one of the most efficient ways to rapidly construct chiral and achiral amine frameworks. Imine reductase (IRED) biocatalysts represent a versatile family of enzymes for amine synthesis through NADPH-mediated imine reduction. The reductive aminases (RedAms) are a subfamily of IREDs that were recently shown to catalyze imine formation as well as imine reduction. Herein, a diverse library of novel enzymes were expressed and screened as cell-free lysates for their ability to facilitate reductive amination to expand the known suite of biocatalysts for this transformation and to identify more enzymes with potential industrial applications. A range of ketones and amines were examined, and enzymes were identified that were capable of accepting benzylamine, pyrrolidine, ammonia, and aniline. Amine equivalents as low as 2.5 were employed to afford up to>99 % conversion, and for chiral products, up to>98 % ee could be achieved. Preparative-scale reactions were conducted with low amine equivalents (1.5 or 2.0) of methylamine, allylamine, and pyrrolidine, achieving up to>99 % conversion and 76 % yield.RED alert: Imine reductases (IREDs) are expressed and screened as cell-free lysates for their ability to facilitate reductive amination. Ketones and amines are examined, and enzymes accepting benzylamine, pyrrolidine, ammonia, and aniline are identified. Amine equivalents as low as 2.5 afford up to>99 % conversion and up to>98 % ee. Preparative-scale reactions with low amine equivalents (1.5 or 2.0) result in up to>99 % conversion and 76 % yield.
      PubDate: 2018-01-11T09:06:39.305662-05:
      DOI: 10.1002/cctc.201701408
       
  • Hydrogenation and Reductive Amination of Aldehydes using Triphos Ruthenium
           Catalysts
    • Authors: Francesca Christie; Antonio Zanotti-Gerosa, Damian Grainger
      Abstract: An air-stable and readily accessible ruthenium dihydride complex catalyses aldehyde hydrogenation under neutral conditions. A high activity has been shown in a number of examples, and solvent-free conditions are also applicable, which favours industrial-scale applications. The catalyst has also been demonstrated to be active at low catalyst loadings for the reductive amination of aldehydes under mildly acidic conditions. A number of examples of chemoselectivity challenges are also presented in which the catalyst does not reduce carbon−halogen groups, alkene or ketone functionality. The advantage of using the pre-formed complex, Triphos-Ru(CO)H2 (1), over in situ formed catalysts from Triphos and Ru(acac)3 (acac=acetylacetonate) is also shown in terms of both chemoselectivity and activity, in particular this can be seen if low reaction temperatures are used.Try Triphos: An air-stable and readily accessible ruthenium dihydride complex catalyzes aldehyde hydrogenation under neutral conditions or reductive amination under mildly acidic conditions. Low catalyst loadings are employed, typically 10 000–100 000:1 substrate/catalyst, which suggests that favorably low catalyst cost contributions are achievable.
      PubDate: 2018-01-11T09:06:32.337753-05:
      DOI: 10.1002/cctc.201701450
       
  • Single-Particle Studies to Advance the Characterization of Heterogeneous
           Biocatalysts
    • Authors: Ana I. Benítez-Mateos; Bernd Nidetzky, Juan M. Bolivar, Fernando López-Gallego
      Abstract: Immobilized enzymes have been widely exploited because they work as heterogeneous biocatalysts, allowing their recovery and reutilization and easing the downstream processing once the chemical reactions are completed. Unfortunately, we suffer a lack of analytical methods to characterize those heterogeneous biocatalysts at microscopic and molecular levels with spatio-temporal resolution, which limits their design and optimization. Single-particle studies are vital to optimize the performance of immobilized enzymes in micro/nanoscopic environments. In this Concept article, we review different analytical techniques that address single-particle studies to image the spatial distribution of the enzymes across the solid surfaces, the sub-particle substrate diffusion, the structural integrity and mobility of the immobilized enzymes inside the solid particles, and the pH and O2 internal gradients. From our view, such sub-particle information elicited from single-particle analysis is paramount for the design and fabrication of optimal heterogeneous biocatalyst.Biocatalysis on the wall: This Concept outlines some of the most relevant advances for the characterization of heterogeneous biocatalysts at single-particle level.
      PubDate: 2018-01-11T09:06:14.529186-05:
      DOI: 10.1002/cctc.201701590
       
  • Selective decomposition of cyclohexyl hydroperoxide using homogeneous and
           heterogeneous Cr(VI) catalysts: Optimizing the reaction by evaluating the
           reaction mechanism
    • Authors: Jessica Nadine Hamann; Marko Hermsen, Anna-Corina Schmidt, Saskia Krieg, Jasmin Schießl, Dominic Riedel, Joaquim Henrique Teles, Ansgar Schäfer, Peter Comba, A. Stephen K. Hashmi, Thomas Schaub
      Abstract: In this study, known homogeneous and heterogeneous chromium(VI) catalyst systems were investigated with respect to the favored formation of cyclohexanone during the decomposition of cyclohexyl hydroperoxide (CHHP). The focus was on mechanistic studies using different spectroscopic methods as well as DFT calculations to further optimize the reaction conditions. As in previous decomposition studies, a mechanism via the formation of a metal alkylperoxido intermediate is probable. In situ spectroscopic studies revealed that in case of both the soluble and insoluble catalyst, the selective decomposition happens via a non-radical, non-redox mechanism at the Cr(VI) stage through the formation of a cyclohexylperoxychromium(VI)¬ complex. The proposed mechanism is supported by thorough DFT calculations.
      PubDate: 2018-01-11T06:20:33.115963-05:
      DOI: 10.1002/cctc.201701909
       
  • Methanation of CO2 over Zeolite-Encapsulated Nickel Nanoparticles
    • Authors: Farnoosh Goodarzi; Liqun Kang, Feng Ryan Wang, Finn Joensen, Søren Kegnæs, Jerrik Mielby
      Abstract: Here we present a simple and effective method to encapsulate Ni nanoparticles in zeolite silicalite-1. In this method, the zeolite is modified by selective desilication, which creates intra-particle voids and mesopores that facilitate the formation of small and well-dispersed nanoparticles upon impregnation and reduction. TEM and XPS analysis confirm that a significant part of the Ni nanoparticles are situated inside the zeolite rather than on the outer surface. The encapsulation results in an increased metal dispersion and, consequently, a high catalytic activity for CO2 methanation. With a gas hourly space velocity of 60000 ml/g catalyst h-1 and H2/CO2=4, the zeolite-encapsulated Ni nanoparticles result in 60% conversion at 450°C, which corresponds to a site-time yield of around 304 mol CH4/mol Ni h-1. The encapsulated Ni nanoparticles show no change in activity or selectivity after 50 h of operation, although post-catalysis characterisation reveals some particle migration.
      PubDate: 2018-01-11T05:31:49.366125-05:
      DOI: 10.1002/cctc.201701946
       
  • Aerobic Oxygenation of Alkylarenes over Ultrafine
           Transition-Metal-Containing Manganese-Based Oxides
    • Authors: Satoru Nakai; Tsubasa Uematsu, Yoshiyuki Ogasawara, Kosuke Suzuki, Kazuya Yamaguchi, Noritaka Mizuno
      Abstract: The oxygenation of alkylarenes to the corresponding aryl ketones is an important reaction, and the development of efficient heterogeneous catalysts that can utilize O2 as the sole oxidant is highly desired. In this study, we developed an efficient alkylarene oxygenation process catalyzed by ultrafine transition-metal-containing Mn-based oxides with spinel or spinel-like structures (M-MnOx, M=Fe, Co, Ni, Cu). These M-MnOx catalysts were prepared by a low-temperature reduction method in 2-propanol-based solutions using tetra-n-butyl ammonium permanganate (TBAMnO4) as the Mn source, and they exhibited high Brunauer–Emmett–Teller surface areas (typically>400 m2 g−1). Using fluorene as the model substrate, the catalytic activities of M-MnOx and Mn3O4 were compared. The catalytic activities of M-MnOx were significantly higher than that of Mn3O4, which demonstrates that the incorporation of transition metals in manganese oxide was critical. Among the series of M-MnOx catalysts examined, Ni-MnOx exhibited the highest catalytic activity for the oxygenation. In addition, the catalytic activity of Ni-MnOx was higher than that of a physical mixture of Mn3O4 and NiO. Furthermore, Ni-MnOx exhibited a broad substrate scope with respect to various types of structurally diverse (hetero)alkylarenes (16 examples). The observed catalysis was truly heterogeneous, and the Ni-MnOx catalyst was reusable for the oxygenation of fluorene at least three times and its high catalytic performance was preserved, for example, the reaction rate, final product yield, and product selectivity. The present Ni-MnOx-catalyzed oxygenation process is possibly initiated by a single-electron oxidation process, and herein a plausible oxygen-transfer mechanism is proposed based on several pieces of experimental evidence.In a spinel: In the presence of ultrafine transition-metal-containing manganese-based oxides with spinel or spinel-like structures, especially Ni-MnOx, various types of structurally diverse (hetero)alkylarenes are converted into the corresponding (hetero)aryl ketones. The observed catalysis is truly heterogeneous, and the Ni-MnOx catalyst is reusable for the oxygenation of fluorene at least three times and its high catalytic performance is preserved.
      PubDate: 2018-01-10T12:26:23.352083-05:
      DOI: 10.1002/cctc.201701587
       
  • Unique Reactivity of Dihydrosilanes under Catalysis by Supported Gold
           Nanoparticles: cis-1,2-Dehydrogenative Disilylation of Alkynes
    • Authors: Iakovos Saridakis; Marios Kidonakis, Manolis Stratakis
      Abstract: In contrast to monohydrosilanes (R3SiH), which in the presence of supported gold nanoparticles primarily undergo typical β-(E)-hydrosilylation reactions with alkynes, dihydrosilanes (R2SiH2) under catalysis of Au/TiO2 lead to cis-1,2-dehydrogenative disilylation reactions at room temperature with high selectivity. The disilyl adducts can be further functionalized through a one-pot procedure, catalyzed by the same catalyst, to form substituted 2,5-dihydro-1,2,5-oxadisiloles or 1,4-disila-2,5-cyclohexadienes.A Si-ght for sore eyes: In contrast to monohydrosilanes (R3SiH), which in the presence of supported gold nanoparticles primarily undergo typical β-(E)-hydrosilylation reactions with alkynes, dihydrosilanes (R2SiH2) under catalysis of Au/TiO2 lead primarily to cis-1,2-dehydrogenative disilylation reactions.
      PubDate: 2018-01-10T12:26:13.8157-05:00
      DOI: 10.1002/cctc.201701526
       
  • Hollow Porous Carbon with in situ Generated Monodisperse Gold
           Nanoclusters for Efficient CO Oxidation
    • Authors: Jiafu Qu; Haiguang Zhu, Dongyun Chen, Najun Li, Qingfeng Xu, Jianping Xie, Hua Li, Jinghui He, Jianmei Lu
      Abstract: Precious metals (Au and Pt) loaded in a mesoporous substrate (carbon and silicon) are popular materials for catalytic CO oxidation. However, the preparation of noble metals and the metal particle size after deposition in the pore channels of the mesoporous materials are serious issues for environmentally friendly applications. Herein, a gold-decorated hollow porous carbon nanospheres (Au/HPCN) catalyst, which is both durable and uniform, is synthesized by a facile in situ reduction route for continuous CO oxidation. In our approach, HPCNs were selected as the substrate because of their thermal stability, well-defined nanostructure, and large surface area. Au nanoclusters were loaded in the pore channels of HPCN because of their stability and catalytic performance. The as-synthesized nanocomposite possesses a uniform size and highly porous structure. Moreover, CO oxidation occurred both during the reduction of Au3+ ions and after the preparation of Au/HPCN.Golden channel walls: A Au/HPCN (hollow porous carbon nanospheres) porous catalyst, which is both durable and uniform, is synthesized by a facile in situ reduction route for continuous and efficient catalytic CO oxidation.
      PubDate: 2018-01-10T12:25:57.796444-05:
      DOI: 10.1002/cctc.201701463
       
  • Hierarchically Structured NiFeOx/CuO Nanosheets/Nanowires as an Efficient
           Electrocatalyst for the Oxygen Evolution Reaction
    • Authors: Steffen Czioska; Jianying Wang, Shangshang Zuo, Xue Teng, Zuofeng Chen
      Abstract: It is desirable to fabricate hierarchically structured NiFe-based materials to further boost the performance of these state-of-the-art electrocatalysts for the oxygen evolution reaction (OER). Most of the NiFeOx catalysts in the form of layered double hydroxides feature a nanosheet structure, which limits their spatial extension at the electrode substrate. Herein, we report the fabrication of unique NiFeOx/CuO nanosheets/nanowires and their use as efficient electrocatalysts for the OER. The surface-bound Cu(OH)2 nanowires were grown in situ on a copper substrate by a simple solution-based method, which were then converted to CuO nanowires by calcination in air. The coating of NiFeOx nanosheets was achieved by anodic co-deposition in concentrated carbonate solution containing NiII and FeIII. The presence of concentrated carbonate anions allows FeIII to be dissolved in a basic solution by complex ion formation. This strategy therefore avoids the destruction of CuO nanowires caused by the usual cathodic procedure in acidic solutions. At a planar copper foil, a small Tafel slope of 36 mV dec−1 was obtained in 1 m KOH and a current density of 100 mA cm−2 was reached at a very low overpotential of 300 mV from the Tafel plot. Electrolysis experiments showed high stability of the catalyst with nearly no loss in efficiency and morphology change after a prolonged period. The same catalyst could be established on a three-dimensional copper foam.NiFe-based electrocatalysts: CuO nanowires were developed by a solution-based method on copper foil or copper foam and an anodic deposition method in basic carbonate buffer solution was utilized for preparation of hierarchically structured NiFeOx/CuO nanosheets/nanowires for high-performance oxygen evolution reactions (OER).
      PubDate: 2018-01-10T12:25:50.506087-05:
      DOI: 10.1002/cctc.201701441
       
  • Sol–Gel Autocombustion Combined Carbothermal Synthesis of Iron-Based
           Catalysts for the Fischer–Tropsch Reaction
    • Authors: Yingying Xue; Yongbiao Zhai, Zheng Chen, Juan Zhang, Jiaqiang Sun, Mohamed Abbas, Yilong Chen, Jiangang Chen
      Abstract: A new combined method of sol–gel autocombustion with carbothermal reduction has been developed to synthesize Fe-based Fischer–Tropsch synthesis (FTS) catalysts. The effect of the glucose content on the structure and texture of the Fe phase is investigated. The glucose is employed as a reducing and carburizing agent to control the phase transformation of the Fe precursors. The reducibility of the synthesized iron oxide increases with the increase of the proportion of glucose. Meanwhile, iron oxide is converted completely into iron carbide in the presence of abundant glucose. The addition of glucose to the precursor is conducive to construct active sites before the FTS reaction. However, excess glucose results in carbon deposition and a poor FTS performance. Iron carbide also could be synthesized by this new method and will be applied directly to the FTS reaction in further research.Sweeten the deal: The glucose content plays a crucial role in the manipulation of the phase, morphology, texture, reduction behavior, and catalytic performance of Fe precursors in this new combined sol–gel autocombustion and carbothermal method.
      PubDate: 2018-01-10T07:00:30.826363-05:
      DOI: 10.1002/cctc.201701424
       
  • Air-stable Ru(II)-NNN Pincer Complexes for Efficient Coupling of Aromatic
           Diamines and Alcohols to 1H-benzo[d]imidazoles with liberation of H2
    • Authors: Lin Li; Qi Luo, Huahua Cui, Renjie Li, Jing Zhang, Tianyou Peng
      Abstract: Abstract: Two new phosphine-free Ru(II)-NNN pincer complexes ([RuCl(L1)(CH3CN)2]Cl (1) and [RuCl(L2)(CH3CN)2]Cl (2), L1 = 2,6-bis(1H-imidazole-2-yl)pyridine, L2 = 2,6-bis(1-hexyl-1H-imidazole-2-yl)pyridine) were synthesized for homogeneously catalyzing the condensation of benzyl alcohol and benzene-1,2-diamine to 2-pheny-1H-benzo[d]imidazole and H2. It was found that the reactivity with an order of 1> 2 is lower than that of the phosphine-containing Ru(II)-NNN pincer complex [RuCl2(L1)(PPh3)3] (3), and thus a homogeneous system containing complex 1, 1 equiv. of 1,2-bis(diphenyl-phosphanyl)ethane (dppe), and 10 equiv. of NaBPh4 was developed to improve the catalytic efficiency for the condensation of primary alcohols and benzene-1,2-diamine (or its derivatives) to 2-substituted 1H-benzo[d]imidazoles in excellent yields (up to 97%) and turnover number (TONs ~ 388). The present system realizes facile one-step synthesis of 1H-benzo[d]imidazole derivatives from alcohols without using the oxidant and/or the stoichiometric amount of inorganic bases that is usually necessary in homogeneous systems reported previously.
      PubDate: 2018-01-10T02:55:23.838264-05:
      DOI: 10.1002/cctc.201800017
       
  • Fabrication of Single-atom Pt Catalyst for Hydrogen Evolution Reaction: A
           New Protocol by Utilization of HxMoO3-x with Plasmon Resonance
    • Authors: Wei Liu; Qun Xu, Pengfei Yan, Jun Chen, Yi Du, Shengqi Chu, Jiaou Wang
      Abstract: Single-atom catalysts (SACs) play a key role in many chemical processes owing to the highly desirable atom efficiency, but the challenging synthesis of the catalysts limits their commercialization or application on a large scale. Here we report a facile strategy to integrate atomically Pt into richly-deficient MoO3-x. The core of the experimental strategy is the fabrication and utilization of HxMoO3-x with plasmon resonance that contains intercalated H+. The obtained catalyst possesses the remarkable electrocatalytic activity toward the hydrogen evolution reaction, which is even comparable with that of the commercial Pt/C. While the application amount of Pt is reduced greatly and it is only 10 percent of the commercial Pt/C. Therefore this work not only supplies a new synthesis route to SACs, but also it reveals the potential relation between plasmon resonance materials and fabrication of single- atom catalyst at the same time.
      PubDate: 2018-01-10T01:55:28.977903-05:
      DOI: 10.1002/cctc.201701777
       
  • Hydrogen Peroxide Production on Carbon Nitride-Boron Nitride-Reduced
           Graphene Oxide Hybrid Photocatalyst under Visible Light
    • Authors: Yusuke Kofuji; Yuki Isobe, Yasuhiro Shiraishi, Hirokatsu Sakamoto, Satoshi Ichikawa, Shunsuke Tanaka, Takayuki Hirai
      Abstract: Photocatalytic production of hydrogen peroxide (H2O2) from earth-abundant water and O2 is one desirable artificial photosynthesis for solar fuel production. We prepared a metal-free hybrid photocatalyst consisting of pyromellitic diimide-doped carbon nitride (g-C3N4/PDI), boron nitride (BN), and reduced graphene oxide (rGO). The g-C3N4/PDI-BN-rGO catalyst, when photoirradiated in water with O2 by visible light at room temperature, efficiently produces H2O2. The photoexcited g-C3N4/PDI moiety transfers the conduction band electrons to rGO, leading to selective production of H2O2 via two-electron reduction of O2 on the rGO surface. In contrast, the valence band holes photoformed on the g-C3N4/PDI moieties are transferred to BN, leading to efficient oxidation of water. The electron-hole separation enhanced by the incorporation of rGO and BN significantly suppresses the charge recombination and exhibits high photocatalytic activity. The solar-to-chemical conversion (SCC) efficiency for H2O2 production on the hybrid catalyst is 0.27 %, which is higher than the highest efficiencies obtained by overall water splitting on powdered catalysts.
      PubDate: 2018-01-09T21:56:15.528383-05:
      DOI: 10.1002/cctc.201701683
       
  • Asymmetric synthesis of chiral halogenated amines using amine
           transaminases
    • Authors: Ayad Dawood; Rodrigo de Souza, Uwe Bornscheuer
      Abstract: Amine transaminases (ATA) are versatile and industrially relevant biocatalysts, catalyzing the transfer of an amine group from a donor to an acceptor molecule. Asymmetric synthesis from a prochiral ketone is the most preferred route to the desired amine product, since it is obtainable at a theoretical yield of 100 %. In addition to the requirement of active and enantioselective ATAs, also the choice of a suitable amine donor is important to save costs and to avoid additional enzymes for shifting the equilibrium and/or recycling of cofactors. In this work, we identified suitable (R)- and (S)-ATAs from Aspergillus fumigatus and Silicibacter pomeroyi, respectively to afford a set of halogen-substituted derivatives of brominated or chlorinated 1-phenyl-2-propanamine, 4-phenylbutan-2-amine and 1-(3-pyridinyl)ethanamine. Optimization of the donor-acceptor-ratio enabled the application of isopropylamine as amine donor resulting in high conversion and amines with 73-99 %ee.
      PubDate: 2018-01-09T08:50:50.977035-05:
      DOI: 10.1002/cctc.201701962
       
  • Biocatalytic Racemization Employing TeSADH: Substrate Scope and Organic
           Solvent Compatibility for Dynamic Kinetic Resolution
    • Authors: Jarosław Popłoński; Tamara Reiter, Wolfgang Kroutil
      Abstract: Racemization in combination with a kinetic resolution is the base for a dynamic kinetic resolution (DKR). Biocatalytic racemization was successfully performed for a broad scope of sec-alcohols by employing a single alcohol dehydrogenase (ADH) variant from Thermoanaerobacter pseudoethanolicus (formerly T. ethanolicus; TeSADH W110A I86A C295A). The catalyst employed as a lyophilized whole cell preparation or cell free extract, which tolerated various non-water miscible organic solvents under micro-aqueous or two-phase conditions, whereby cyclohexane and n-hexane suited best. Various concepts for combining the enzymatic racemization with an enzymatic kinetic resolution to achieve overall a bis-enzymatic DKR were evaluated. A proof of concept showed a successful DKR with racemization in aqueous phase combined with acylation in the organic phase.Racemization—Yes it can: Investigation of the substrate scope of a thermophilic alcohol dehydrogenase variant demonstrated its applicability for racemization of sec-alcohols. The racemization under various conditions (buffer, micro aqueous, biphasic) was evaluated with the aim of getting closer to the efficient bis-enzymatic dynamic kinetic resolution of sec-alcohols.
      PubDate: 2018-01-09T08:40:40.834635-05:
      DOI: 10.1002/cctc.201701395
       
  • Efficient Mukaiyama–Aldol Reaction with Aqueous Formaldehyde on a
           Hydrophobic Mesoporous Lewis Acid Polymer
    • Authors: Fang Zhang; Chao Liang, Zhen Wang, Hexing Li
      Abstract: The design of robust water-compatible solid Lewis acid catalysts in the efficient utilization of aqueous formaldehyde is a challenging task. Herein, we describe an ytterbium triflate containing ordered mesoporous polymer (Yb(OTf)2-MP) that acts as a highly active and selective Lewis acid catalyst for the Mukaiyama–aldol reaction with aqueous formaldehyde. The unique capacity of hydrophobic surface and ordered mesoporosity was able to stabilize the hydrophilic and hydrophobic reactants simultaneously and catalyze the reaction selectively by minimizing water interference at active sites. Accordingly, it enabled a broad range of silyl enol ethers to be used to create structurally diverse β-hydroxy carbonyl molecules efficiently. Notably, the process can be scaled up easily to achieve the gram-scale production of the key intermediate of natural product sarkomycin. Additionally, it is stable under aqueous conditions and can be recovered easily and used repeatedly at least six times.Formaldehyde on form: A hydrophobic mesoporous polymer that contains ytterbium triflate enables the efficient Mukaiyama–aldol reaction with aqueous formaldehyde without any additives or organic medium as a cosolvent in water. This highly active and selective heterogeneous transformation provides an environmentally friendly way to create a series of structurally diverse β-hydroxy carbonyl molecules.
      PubDate: 2018-01-09T08:40:36.768028-05:
      DOI: 10.1002/cctc.201701426
       
  • Catalytic N−H Bond Activation and Breaking by a Well-Defined CoII1O4
           Site of a Heterogeneous Catalyst
    • Authors: Konstantin Khivantsev; Alessandro Biancardi, Mahdi Fathizadeh, Fahad Almalki, Job L. Grant, Huynh Ngoc Tien, Abolfazl Shakouri, Douglas A. Blom, Thomas M. Makris, John R. Regalbuto, Marco Caricato, Miao Yu
      Abstract: Catalytic N−H bond activation and breaking by well-defined molecular complexes or their heterogeneous analogues is considered to be a challenge in chemical science. Metal(0) nanoparticles catalytically decompose NH3; they are, however, ill defined and contain a range of contiguous metal sites with varying coordination numbers and catalytic properties. So far, no well-defined/molecular Mn+-containing materials have been demonstrated to break strong N−H bonds catalytically, especially in NH3, the molecule with the strongest N−H bonds. Recently, noncatalytic activation of NH3 with the liberation of molecular H2 on an organometallic molybdenum complex was demonstrated. Herein, we show the catalytic activation and breaking of N−H bonds on a singly dispersed, well-defined, and highly thermally resistant (even under reducing environments) CoII1O4 site of a heterogeneous catalyst for organic (ethylamine) and inorganic (NH3, with the formation of N2 and H2) molecules. The single-site material serves as a viable precursor to ultrasmall (2.7 nm and less) silica-supported cobalt nanoparticles; thus, we directly compare the activity of isolated cationic cobalt sites with small cobalt nanoparticles. Density functional theory (DFT) calculations suggest a unique mechanism involving breaking of the N−H bonds in NH3 and N−N coupling steps taking place on a Co1O4 site with the formation of N2H4, which then decomposes to H2 and N2H2; N2H2 subsequently decomposes to H2 and N2. In contrast, Co1N4 sites are not catalytically active, which implies that the ligand environment around a single atom of a heterogeneous catalyst largely controls reactivity. This may open a new chapter for the design of well-defined heterogeneous materials for N−H bond-activation reactions.A site to behold: We show the catalytic activation and breaking of N−H bonds on the singly dispersed, well-defined, and highly thermally resistant CoII1O4 sites of a heterogeneous catalyst for both organic and inorganic molecules. The catalytic activity of the single sites is directly compared to that of ultrasmall supported cobalt nanoparticles. DFT calculations suggest a novel mechanism involving N−H bond breaking and N−N coupling steps occurring on CoII1O4 sites.
      PubDate: 2018-01-09T07:15:55.00385-05:0
      DOI: 10.1002/cctc.201701268
       
  • Cu-Co-Ce Ternary Oxide as an additive to conventional PGM catalyst for
           automotive exhaust catalysis
    • Authors: Andrew Justin Binder; Todd J. Toops, James E. Parks II
      Abstract: Recently we reported on a ternary mixed oxide catalyst which showed low temperature CO oxidation activity in lean exhaust conditions without inhibition by hydrocarbons such as propene. However, this Cu-Co-Ce catalyst's (CCC) hydrocarbon oxidation activity cannot be considered as a stand-alone solution to low temperature automotive exhaust catalysis. To achieve both low temperature oxidation of pollutants and a reduction of total PGM content we have examined a 50% physical mixture of traditional Pt/Al2O3 and our CCC catalyst in two simulated exhaust protocols. Using this physical mixture, we are able to obtain equivalent or better hydrocarbon activity to the baseline Pt/Al2O3 catalyst with half of the total PGM content as well as an increased sulfur tolerance for the CCC component of the mixture. DRIFTS data confirms that despite exposure of sulfur-sensitive CCC to SO2, Cu+-carbonyl binding sites can still be seen when the catalyst is mixed with Pt/Al2O3.
      PubDate: 2018-01-08T21:50:51.261639-05:
      DOI: 10.1002/cctc.201701706
       
  • Vanadium-Catalyzed Deoxydehydration of Glycerol Without an External
           Reductant
    • Authors: Allan R. Petersen; Lasse B. Nielsen, Johannes R. Dethlefsen, Peter Fristrup
      Abstract: A vanadium-catalysed deoxydehydration (DODH) of neat glycerol has been developed. Cheap and readily available ammonium metavanadate (NH4VO3) affords higher yields of allyl alcohol than the well-established catalyst methyltrioxorhenium. A study in which deuterium-labelled glycerol was used was undertaken to further elucidate the dual role of glycerol as both an oxidant and reductant. This study led to the proposal of a metal-catalysed DODH mechanism for the production of allyl alcohol and a deeper understanding of the formation of the byproducts acrolein and propanal.Va va vanadium! The vanadium-catalyzed deoxydehydration of neat glycerol using cheap and readily available ammonium metavanadate (NH4VO3) affords higher yields of allyl alcohol than the use of the well-established catalyst methyltrioxorhenium. The use of deuterium-labeled glycerol helped to elucidate the dual role of glycerol as both oxidant and reductant and to understand the formation of byproducts acrolein and propanal.
      PubDate: 2018-01-08T09:45:25.378046-05:
      DOI: 10.1002/cctc.201701049
       
  • Exceptionally Efficient and Recyclable Heterogeneous Metal–Organic
           Framework Catalyst for Glucose Isomerization in Water
    • Authors: Ryan Oozeerally; David L. Burnett, Thomas W. Chamberlain, Richard I. Walton, Volkan Degirmenci
      Abstract: Heterogeneous catalysts are desired for the conversion of glucose, the most abundant sugar in renewable biomass, but presently their synthesis requires highly toxic chemicals with long synthesis times. We report the conversion of glucose into fructose and 5-hydroxymethylfurfural on a heterogeneous catalyst that is stable and selective and operates in the most environmentally benign solvent, water. We used a bifunctional solid with Lewis and Brønsted acid sites by partially replacing the organic linker of the zirconium organic framework UiO-66 with 2-monosulfo-benzene-1,4-dicarboxylate. This catalyst showed high product selectivity (90 %) to 5-hydroxymethylfurfural and fructose at 140 °C in water after a reaction time of 3 h. It was recyclable and showed only a minor loss in activity after the third recycle, offering a realistic solution for the bottleneck glucose isomerization reaction for scale-up and industrial application of biomass utilization.A sweet deal: A highly selective metal–organic framework catalyst (UiO-66-MSBDC) for the conversion of glucose into fructose and 5-hydroxymethylfurfural (HMF) is presented. The catalyst operates in water at little over 100 °C, providing benign conditions with nontoxic reagents. It is recyclable and is constructed from readily available and inexpensive organic ligands.
      PubDate: 2018-01-08T08:05:42.609589-05:
      DOI: 10.1002/cctc.201701825
       
  • Panel of New Thermostable CYP116B Self-Sufficient Cytochrome P450
           Monooxygenases that Catalyze C−H Activation with a Diverse Substrate
           Scope
    • Authors: Michele Tavanti; Joanne L. Porter, Selina Sabatini, Nicholas J. Turner, Sabine L. Flitsch
      Abstract: The ability of cytochrome P450 monooxygenases to catalyse a wide variety of synthetically challenging C−H activation reactions makes them highly desirable biocatalysts both for the synthesis of chiral intermediates and for late-stage functionalisations. However, P450s are plagued by issues associated with poor expression, solubility and stability. Catalytically self-sufficient P450s, in which the haem and reductase domains are fused in a single protein, obviate the need for additional redox partners and are attractive as biocatalysts. Here we present a panel of natural self-sufficient P450s from thermophilic organisms (CYP116B65 from A. thermoflava, CYP116B64 from A. xiamenense, CYP116B63 from J. thermophila, CYP116B29 from T. bispora and CYP116B46 from T. thermophilus). These P450s display enhanced expression and stability over their mesophilic homologues. Activity profiling of these enzymes revealed that each P450 displayed a different fingerprint in terms of substrate range and reactivity that cover reactions as diverse as hydroxylation, demethylation, epoxidation and sulfoxidation. The productivity of the bio-transformation of diclofenac to produce the 5-hydroxy metabolite increased 42-fold using the thermostable P450-AX (>0.5 g L−1 h−1) compared to the P450-RhF system reported previously. In conclusion, we have generated a toolkit of thermostable self-sufficient P450 biocatalysts with a broad substrate range and reactivity.Looking to nature: P450s are often limited by poor expression, stability, and efficiency. The use of catalytically self-sufficient P450s from thermophilic organisms combines naturally evolved stability and efficiency conveniently to yield biocatalysts suitable for further engineering and industrial application.
      PubDate: 2018-01-08T08:05:35.696684-05:
      DOI: 10.1002/cctc.201701510
       
  • Kinetic Resolution and Deracemization of Racemic Amines Using a Reductive
           Aminase
    • Authors: Godwin A. Aleku; Juan Mangas-Sanchez, Joan Citoler, Scott P. France, Sarah L. Montgomery, Rachel S. Heath, Matthew P. Thompson, Nicholas J. Turner
      Abstract: The NADP(H)-dependent reductive aminase from Aspergillus oryzae (AspRedAm) was combined with an NADPH oxidase (NOX) to develop a redox system that recycles the co-factor. The AspRedAm-NOX system was applied initially for the kinetic resolution of a variety of racemic secondary and primary amines to yield S-configured amines with enantiomeric excess (ee) values up to 99 %. The addition of ammonia borane to this system enabled the efficient deracemization of racemic amines, including the pharmaceutical drug rasagiline and the natural product salsolidine, with conversions up to>98 % and>99 % ee Furthermore, by using the AspRedAm W210A variant it was possible to generate the opposite R enantiomers with efficiency comparable to, or even better than, the wildtype AspRedAm.A race against time: The reductive aminase from Aspergillus oryzae (AspRedAm) is combined with NADPH oxidase (NOX) to enable the kinetic resolution of a variety of racemic amines to yield S-configured products. The corresponding R enantiomers are obtained by the use of a single amino acid variant, AspRedAm W210A. Furthermore, an AspRedAm-NOX-NH3⋅BH3 cascade is constructed to allow the efficient deracemization of racemic amines.
      PubDate: 2018-01-08T05:35:29.280876-05:
      DOI: 10.1002/cctc.201701484
       
  • Direct Synthesis of Lactams from Keto Acids, Nitriles, and H2 by
           Heterogeneous Pt Catalysts
    • Authors: S. M. A. H. Siddiki; Abeda S. Touchy, Ashvini Bhosale, Takashi Toyao, Yuji Mahara, Junya Ohyama, Atsushi Satsuma, Ken-ichi Shimizu
      Abstract: We report herein the first general catalytic system for the direct synthesis of N-substituted γ- and δ-lactams by reductive amination/cyclization of keto acids (including levulinic acid) with nitriles and H2 under mild conditions (7 bar H2, 110 °C, solvent free). The most effective catalyst, Pt and MoOx co-loaded TiO2 (Pt-MoOx/TiO2), shows a wide substrate scope, high turnover number (TON), and good reusability.Lactams in one pot: The first general and reusable catalytic system for the one-pot synthesis of N-substituted lactams by reductive conversion of keto acids (including levulinic acid) with nitriles and H2 under mild conditions is reported.
      PubDate: 2018-01-05T07:16:01.229022-05:
      DOI: 10.1002/cctc.201701355
       
  • Hollow Structure and Electron Promotion Effect of Mesoporous Pd/CeO2
           Catalyst for Enhanced Catalytic Hydrogenation
    • Authors: Qinhong Wei; Qingxiang Ma, Pingping Zuo, Huailin Fan, Shijie Qu, Wenzhong Shen
      Abstract: A hollow structured CeO2 spheres supported metallic Pd catalyst (Pd/CeO2-H) was designed and prepared by a glucose hydrothermal method and impregnation method. The CeO2-H consisted of an inner hollow cavity and an outer shell on which a large number of mesopores were formed. The Pd/CeO2-H hollow sphere catalyst, which presented abundant surface oxygen vacancies, was investigated for catalytic hydrogenations of styrene and nitrobenzene to produce ethylbenzene and aniline. Activity tests indicated that the mesoporous Pd/CeO2-H hollow sphere catalyst exhibited striking catalytic activity, which was attributed to the spatial core–shell structure that provided more active sites and facilitated reactant diffusion as well as surface defects (oxygen vacancies), which were capable of transferring electrons to metallic Pd. All of these advances are beneficial to give a higher catalytic hydrogenation performance.Hollow hydrogenation: A hollow CeO2 spheres supported metallic Pd catalyst was prepared by employing a glucose hydrothermal method and impregnation method. The Pd/CeO2 hollow sphere catalyst, which consisted of a hollow cavity and outer shell, presented a higher catalytic hydrogenation performance of styrene and nitrobenzene to produce ethylbenzene and aniline, better than that of the general CeO2-supported Pd catalyst.
      PubDate: 2018-01-05T07:15:52.691784-05:
      DOI: 10.1002/cctc.201701457
       
  • An Effective Catalytic Hydroboration of Alkynes in Supercritical CO2 under
           Repetitive Batch Mode
    • Authors: Jakub Szyling; Adrian Franczyk, Kinga Stefanowska, Mateusz Klarek, Hieronim Maciejewski, Jędrzej Walkowiak
      Abstract: A facile method for the synthesis of unsaturated organoboron compounds by hydroboration of terminal and internal alkynes in supercritical (sc) CO2 has been presented for the first time. The reactions performed in scCO2 in the presence of Ru catalysts (selectivity, productivity) are compared with those in a traditionally used solvent or without it. Moreover, the catalytic systems based on the application of scCO2 have been successfully tested for the processes under repetitive batch conditions. This strategy permitted us to obtain boryl-substituted olefins with high yields and selectivities up to the 16th catalytic cycle if using Ru(CO)Cl(H)(PPh3)3 as a catalyst. The process applied the self-dosing catalyst, which is gradually released to the reaction mixture under supercritical conditions in the individual batch. Such an approach has a positive impact on process sustainability and economy.Batch by batch: A facile method for the synthesis of unsaturated organoboron compounds by hydroboration of terminal and internal alkynes in supercritical (sc) CO2 is presented. The scCO2 catalytic systems have been successfully tested for the processes under repetitive batch conditions. This strategy permitted boryl-substituted olefins to be obtained with high yields and selectivities up to the 16th catalytic cycle if using Ru(CO)Cl(H)(PPh3)3 as a catalyst.
      PubDate: 2018-01-05T07:15:44.178818-05:
      DOI: 10.1002/cctc.201701318
       
  • A Bunch-like Copper Oxide Nanowire Array as an Efficient, Durable, and
           Economical Catalyst for the Methanolysis of Ammonia Borane
    • Authors: Liang Cui; Xueying Cao, Xuping Sun, Wenrong Yang, Jingquan Liu
      Abstract: The dehydrogenation of ammonia borane (AB) is an effective method to produce and store hydrogen, but efficient, durable, and low-costing dehydrogenation catalysts are lacking. In this work, we successfully prepared a self-supported bunch-like copper oxide nanowire array on copper foam (b-CuO NA/CF) through a facile in situ wet oxidation and annealing method. b-CuO NA/CF shows high catalytic activity for the methanolysis of AB with an initial turnover frequency of 13.3 molH2 molCuO−1 min−1 and an activation energy of 34.7 kJ mol−1. Moreover, this self-supported bunch-like nanoarray catalyst could be easily separated from fuel solutions with excellent stability and maintained its activity even after prolonged use. It is thus an efficient, economical, and durable catalyst for hydrogen fuel cells.Pick of the bunch: A bunch-like CuO nanowire array on copper foam (b-CuO NA/CF) is obtained by a facile and economical method. This nanowire array behaves as an efficient and durable catalyst for hydrogen generation from the controlled methanolysis of ammonia borane (AB).
      PubDate: 2018-01-05T07:15:35.562836-05:
      DOI: 10.1002/cctc.201701317
       
  • Insight into the Synergism between Copper Species and Surface Defects
           Influenced by Copper Content over Copper/Ceria Catalysts for the
           Hydrogenation of Carbonate
    • Authors: Huabo Li; Yuanyuan Cui, Qianqian Liu, Wei-Lin Dai
      Abstract: Various Cu/CeO2 nanorod catalysts with different copper contents were synthesized through a facile coprecipitation method for the hydrogenation of diethyl carbonate to methanol in a fixed-bed reactor. The methanol yield increased upon increasing the copper loading, but large excess amounts of copper led to deactivation of the catalyst at a high liquid hourly space velocity because of aggregation of the active metal. The 20Cu/CeO2 and 30Cu/CeO2 catalysts displayed superior catalytic performance with methanol space-time yields of 8.4 and 8.1 mmol gcat−1 h−1, respectively. The remarkably enhanced catalytic performance was mainly ascribed to a high Cu0 surface area, appropriate ratio of Cu+/Cu0, and more surface oxygen vacancies associated with Ce3+, which stemmed from a strong interaction between Cu and the CeO2 support.Synergistic catalysis: Cu/CeO2 catalysts with a proper copper content achieve superb activity for the vapor-phase continuous hydrogenation of diethyl carbonate to methanol. The enhanced catalytic performance is attributed mainly to synergism between the active copper species and the surface defects of the CeO2 support.
      PubDate: 2018-01-05T07:15:28.589485-05:
      DOI: 10.1002/cctc.201701384
       
  • Ring-Expanded N-Heterocyclic Carbenes for Copper-Mediated Azide-Alkyne
           Click Cycloaddition Reactions
    • Authors: Filip Sebest; Jay J Dunsford, Matthew Adams, Jeremy Pivot, Paul D Newman, Silvia Díez-González
      Abstract: A series of well-defined copper(I) complexes bearing ring expanded N-heterocyclic carbene (NHC) ligands has been applied to the azide-alkyne cycloaddition reaction. The obtained results notably showed that the six membered NHC ligands outperform well-established five-membered ones. [CuI(Mes-6)] displayed a remarkable catalytic activity while respecting the strict criteria for Click reactions.
      PubDate: 2018-01-05T06:25:41.979709-05:
      DOI: 10.1002/cctc.201701992
       
  • A Quantification of the Soai Reaction
    • Authors: María E. Noble-Terán; José-Manuel Cruz, Jean-Claude Micheau, Thomas Buhse
      Abstract: A kinetic and thermodynamic model of the Soai reaction is presented. This allows the quantitative determination of five rates constants and one equilibrium constant. The model is realistic as it integrates the results of the most recently published XRD structural data and DFT calculations and selected experimental kinetic data. Equipped with the extracted parameters from the numerical fitting of the time evolution of both the substrate concentration and the enantiomeric excess, the model was able to mimic strong asymmetric amplification from extremely low initial enantiomeric excess and spontaneous mirror-image symmetry breaking under “zero-catalyst” conditions. It also reproduces the crystallization conditions by exhibiting the preferential accumulation of the corresponding oligomeric species in solution. An important point is also illustrated: the autocatalytic asymmetric amplification is not located on the expected easily detectable dimers but on the less concentrated tetrameric species.Pseudoelementary my dear Watson: A kinetic and thermodynamic model of the Soai reaction is presented. This allows the quantitative determination of five rates constants and one equilibrium constant. The model is realistic as it integrates the results of the most recently published XRD structural data and DFT calculations and selected experimental kinetic data.
      PubDate: 2018-01-05T06:00:34.947533-05:
      DOI: 10.1002/cctc.201701554
       
  • Structure Sensitivity of Acrolein Hydrogenation by Platinum Nanoparticles
           on BaxSr1−xTiO3 Nanocuboids
    • Authors: Christopher M. Engelhardt; Robert M. Kennedy, James A. Enterkin, Kenneth R. Poeppelmeier, Donald E. Ellis, Christopher L. Marshall, Peter C. Stair
      Abstract: The structure sensitivity of Pt nanoparticles (PtN) for gas-phase acrolein (AC) hydrogenation was probed for PtN on BaxSr1−xTiO3 nanocuboid supports with (0 0 1) facets in a combined theoretical and experimental study. The in situ selectivity for allyl alcohol increased with the increase of the Sr concentration in the support, which corresponds to modifications in the stable Winterbottom shape and lattice strain of the Pt nanoparticles as a result of the interfacial energy between Pt and the BaxSr1−xTiO3 supports. “Local model” nanofacets of the Pt surface, edge, and corner morphologies were developed as compact representations of adsorption and reaction sites. DFT was used as the primary modeling tool for the equilibrium adsorption states. We argue that adsorption on edge sites is critically important for the overall allyl alcohol selectivity of PtN catalysts. A simple model was developed to represent PtN strain effects caused by its interaction with the substrate. Bader topological atom, spherical volume averaging charge, and modified bond valence sum analyses were used to understand the bonding structure. Density of states analysis was performed for the structures of PtN, adsorbed AC, and intermediate products to examine adsorbate–particle interactions. The simulated hydrogenation of AC on PtN nanofacets was compared to the in situ hydrogenation of AC by PtN on BaxSr1−xTiO3 to examine the effects of facet, edge, and corner sites on the overall selectivity.Multi-faceted: The structure sensitivity of Pt nanoparticles (PtN) for gas-phase acrolein hydrogenation is probed for PtN on BaxSr1−xTiO3 nanocuboid supports with (0 0 1) facets in a combined theoretical and experimental study. The in situ selectivity for allyl alcohol increases with the increase of the Sr concentration in the support.
      PubDate: 2018-01-05T06:00:30.811085-05:
      DOI: 10.1002/cctc.201701505
       
  • Zeolite-Y-Mediated Multicomponent Reaction of Isatins, Cyclic
           1,3-Diketones, and 1,2-Phenylenediamine: Easy Access to
           Spirodibenzo[1,4]diazepines
    • Authors: Kajal De; Piyali Bhanja, Asim Bhaumik, Chhanda Mukhopadhyay
      Abstract: A facile and efficient one-pot, three-component approach for the synthesis of spirodibenzo[1,4]diazepine derivatives has been achieved by the reaction of isatins, cyclic 1,3-diketones, and 1,2-phenylenediamines in the presence of a Zeolite-Y nanopowder catalyst. The Zeolite-Y nanopowder catalyst was synthesized and characterized thoroughly by using XRD, high-resolution transmission electron microscopy, energy-dispersive spectroscopy, and N2-adsorption analysis. We used X-ray photoelectron spectroscopy to investigate the electronic environment and oxidation state of the elements.Spiralize: A new strategy towards the synthesis of biologically potent spirodibenzo[1,4]diazepine derivatives using recyclable Zeolite-Y as an effective acid catalyst is described. The Zeolite-Y catalyst shows significant advantages over homogeneous catalysts, which include an easy work-up and excellent reusability.
      PubDate: 2018-01-05T03:15:31.336016-05:
      DOI: 10.1002/cctc.201701487
       
  • Continuous-flow Pd-catalyzed synthesis of cyclohexanones from phenols
           using sodium formate as a safe hydrogen source
    • Authors: Luigi Vaccaro; Federica Valentini, Niccolò Santillo, Chiara Petrucci, Daniela Lanari, Elena Petricci, Maurizio Taddei
      Abstract: We report a procedure for the continuous flow production of cyclohexanone from phenol, based on the use of sodium formate as a biomass derived source of hydrogen and on Pd/C as an easily accessible catalytic system. The reaction works in water at pH = 12.0 and at 90 °C. by setting a packed reactor charged with the catalyst Pd/C (10 wt%) at a flow rate of 0.5 mL min-1 we achieved a continuous flow production of cyclohexanone with high yields, selectivity and productivity.
      PubDate: 2018-01-04T22:01:56.834313-05:
      DOI: 10.1002/cctc.201701922
       
  • Porous Organic Polymers Constructed from Tröger's Base as Efficient
           Carbon Dioxide Adsorbents and Heterogeneous Catalysts
    • Authors: Zhifeng Dai; Yongquan Tang, Qi Sun, Xiaolong Liu, Xiangju Meng, Feng Deng, Feng-Shou Xiao
      Abstract: Through a radical solvothermal polymerization method, we synthesized two porous organic polymers based on Tröger's base (POP-TB and POP-Me-TB) from the corresponding vinyl-functionalized monomers (2,8-divinyl-6H,12H-5,11-methanodibenzo[b,f]diazocine and 2,8-divinyl-4,10-dimethly-6H,12H-5,11-ethanodibenzo[b,f]diazocine; v-TB and v-Me-TB). The structure and porosity of these polymers are verified by using solid-state NMR spectroscopy, elemental analysis, SEM, TEM, N2 sorption isotherms, and CO2 sorption tests. They exhibit high surface areas and moderate pore volumes, which give high CO2 adsorption capacities (90 and 71 mgCO2 g−1 at 273 K and 60 and 44 mgCO2 g−1 at 298 K for POP-TB and POP-Me-TB, respectively) under a CO2 pressure of 1 bar. In addition, they display excellent catalytic activities together with highly stability as heterogeneous catalysts in the benchmark Knoevenagel reactions.Basic instinct: Porous organic polymers constructed from Tröger's base are highly efficient for CO2 capture and Knoevenagel reactions.
      PubDate: 2018-01-04T09:10:47.516248-05:
      DOI: 10.1002/cctc.201701534
       
  • Copper-Catalyzed C2 and C3 Phosphonation of Benzofuran and Benzothiophene
           with Trialkyl Phosphites
    • Authors: Yufeng Wang; Yajie Yang, Kun Jie, Ling Huang, Shengmei Guo, Hu Cai
      Abstract: A strategy for the selective phosphonation of benzofuran and benzothiophene with trialkyl phosphites was developed. In these reactions, the C−H phosphonation of benzofurans or benzothiophenes at the C2 or C3 position with trialkyl phosphites was successfully achieved without directing groups by using a copper catalyst. Additionally, the C5 phosphonation of furan was successful under the same conditions.C-3 P–O: A noble-metal-free method for the C2 and C3 phosphonation of benzofuran (benzothiophene) with trialkyl phosphites is developed. The title reaction can be successfully achieved without directing groups by using a copper catalyst. Furthermore, the C5 phosphonation of furan can be performed under the same conditions.
      PubDate: 2018-01-04T09:10:28.765016-05:
      DOI: 10.1002/cctc.201701361
       
  • Sprout-like Growth of Mesoporous Mo2C/NC Nanonetworks as Efficient
           Electrocatalysts for Hydrogen Evolution
    • Authors: Meihong Fan; Yuenan Zheng, Ang Li, Yali Ma, Qisheng Huo, Zhen-An Qiao, Sheng Dai
      Abstract: Owing to their high surface areas, porous networks, nanosized walls, and unique electronic structure, mesoporous metal carbides with tailored nanoarchitectures are of particular interest for their prominent potential applications in various fields, including energy storage, fuel cells, and catalysis. Herein, we report a sprout-like growth strategy for the preparation of a mesoporous β-Mo2C nanonetwork embedded in a nitrogen-rich carbon matrix. The nanoarchitecture can be tailored from a mesoporous Mo2C nanonetwork film into Mo2C nanoparticles embedded into the carbon layer. The as-prepared β-Mo2C material was demonstrated to drive a current density of 10 mA cm−2 at a low overpotential of 140 mV for the hydrogen evolution reaction (HER) in acidic conditions and to remain stable for at least 120 h. The excellent electrocatalytic performance may be from (1) mesoporous Mo2C frameworks offering numerous accessible active sites; (2) a carbon layer that protects the Mo2C from accumulation and favors electron transportation; and (3) shortened diffusion paths and ultrafine crystallinity that benefit its catalytic performance.H2 evolution catalyst: A facile and efficient approach, referred to as a “sprout-like growth” strategy, is reported for the fabrication of a new type of mesoporous Mo2C/NC composite film with a mesoporous Mo2C nanonetwork immobilized and embedded within an N-doped carbon sheet as an excellent hydrogen evolution reaction (HER) catalyst.
      PubDate: 2018-01-04T03:21:10.654182-05:
      DOI: 10.1002/cctc.201701417
       
  • Predispersed Carbocatalyst: Vertically Aligned Nitrogen-Doped Graphene
           Rooted on SiC Microspheres for Selective Oxidation
    • Authors: Jun Ma; Nan Wu, Shi-an Sun, Ting Yao, Gong-yi Li, Tian-jiao Hu, Yi-he Li, Xiao-dong Li
      Abstract: Vertically aligned N-doped graphene rooted on SiC microspheres (NG on SiC) is prepared by precursor pyrolysis. One of the raw materials, acetonitrile, has three important effects that could facilitate the N-doping process effectively, promote the lateral dimensions and improve the graphitization degree of NG on SiC significantly. The metal-free carbocatalyst NG on SiC is an effective and selective oxidation catalyst towards targeted C−H bond activation of ethylbenzene. The unique nanostructure of NG on SiC is composed of predispersed graphene, which is expected to avoid harmful agglomeration during preparation, storage, transportation, and applications.Stack it up! Vertically aligned N-doped graphene rooted on SiC microspheres (NG on SiC) is prepared by precursor pyrolysis by using a lab-made continuous preparation system. The use of acetonitrile as a raw material promotes the lateral dimensions and improves the graphitization degree of NG on SiC significantly. The metal-free carbocatalyst NG on SiC is an effective and selective oxidation catalyst towards targeted C−H bond activation of ethylbenzene.
      PubDate: 2018-01-04T03:21:00.834646-05:
      DOI: 10.1002/cctc.201701239
       
  • Nanodiamond-Core-Reinforced, Graphene-Shell-Immobilized Platinum
           Nanoparticles as a Highly Active Catalyst for the Low-Temperature
           Dehydrogenation of n-Butane
    • Authors: Jiayun Zhang; Xiangbin Cai, Kuang-Hsu Wu, Yajie Zhang, Jia Wang, Jiangyong Diao, Ning Wang, Hongyang Liu, Dangsheng Su
      Abstract: Pt nanoparticles (NPs) immobilized on a core–shell hybrid carbon support allow the efficient direct dehydrogenation of n-butane at low temperatures. The hybrid carbon support is composed of a nanodiamond core and a reinforced ultrathin graphene shell (ND@G), which improves the stability of the anchored Pt NPs against sintering under the reaction conditions. The as-prepared Pt/ND@G catalyst demonstrates excellent catalytic performance (≈25 % conversion with>95 % selectivity toward olefins) at 450 °C for over 10 h as a result of strong metal–support interactions. The catalyst can also be fully regenerated by postoxidative thermal treatment.Core strength: Herein, we show that Pt nanoparticles (NPs) on a hybrid carbon support composed of a nanodiamond core and a reinforced ultrathin graphene shell (i.e., Pd/ND@G) is an efficient catalyst for the direct dehydrogenation of n-butane at low temperatures. The hybrid carbon support stabilizes smaller NPs and prevents them from sintering during the reaction, which is likely the result of strong metal–support interactions.
      PubDate: 2018-01-04T03:20:50.057625-05:
      DOI: 10.1002/cctc.201701231
       
  • Commercial gold(I) and gold(III) compounds supported on carbon materials
           as greener catalysts for the oxidation of alkanes and alcohols
    • Authors: Sonia A. C. Carabineiro; Luísa M.D.R.S. Martins, Armando J.L. Pombeiro, José L Figueiredo
      Abstract: The present paper reports strategies for oxidative functionalization of cyclohexane and alcohols, under mild conditions, catalysed by Au(I) or Au(III) compounds, namely, dichloro(2-pyridinecarboxylato)gold(III) (1), tetrabutylammonium tetrachloroaurato(III) (2), chlorotrimethylphosphinegold(I) (3), chlorotriphenylphosphinegold(I) (4) and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidenegold(I) chloride (5) supported on different carbon materials: activated carbon (AC), multi-walled carbon nanotubes (CNT) and carbon xerogel (CX), with three different surface treatments: original, as purchased/prepared, oxidized with nitric acid (-ox), and oxidized with nitric acid and subsequently treated with NaOH (-ox-Na). The obtained materials were tested for the oxidation of cyclohexane. All materials were very selective to the production of cyclohexanol and cyclohexanone with no trace of by-products detected. The same catalysts were tested in the selective oxidation of methyl benzyl alcohol, cyclohexanol and 2-octanol, to the corresponding aldehydes or ketones. It was found that better results were obtained for the heterogenised complexes and that the most efficient support is CNT-ox-Na. The best result for cyclohexane oxidation was obtained for 5/CNT-ox-Na, which showed recyclability up to 5 cycles without decrease of activity. The highest activity for methyl benzyl alcohol oxidation was found for the 3/CNT-ox-Na material, which could be recycled to 7 cycles without loss of activity.
      PubDate: 2018-01-03T10:55:56.728226-05:
      DOI: 10.1002/cctc.201701886
       
  • A seed-mediated approach for the preparation of modified heterogeneous
           catalysts
    • Authors: Katerina Soulantica; Justine Harmel, Adrien Berliet, Kassiogé Dembélé, Cécile Marcelot, Anne-Sophie Gay, Ovidiu Ersen, Sylvie Maury, Antoine Fécant, Bruno Chaudret, Philippe Serp
      Abstract: Abstract: Colloidal chemistry is very efficient in providing nanocrystals of well controlled structural characteristics. While nanoparticles are essential components of heterogeneous catalysts, colloidal methods are rarely employed for their preparation. We have employed a seed mediated growth approach for modifying the structural characteristics of a conventional cobalt-based Fischer-Tropsch catalyst. The Co particles of this catalyst can play the role of seeds for the overgrowth of shape and structure controlled cobalt nanostructures using a simple wet chemical method involving a molecular cobalt precursor and stabilizing agents. Thus, cobalt nanorods exhibiting the hexagonal compact structure were selectively grown on the immobilized Co particles of a reference Co/Al2O3-SiO2 catalyst. The as obtained catalyst shows a better stability than a reference catalyst for the Fischer-Tropsch reaction. The removal of most of the ligands from the nanorod catalyst allows improving the catalyst activity while maintaining its stability. This is a proof of concept concerning the implementation of wet chemistry nanoparticle synthesis for the modification of heterogeneous catalysts.
      PubDate: 2018-01-03T07:46:46.60841-05:0
      DOI: 10.1002/cctc.201701860
       
  • Vinyldiazo Reagents and Metal Catalysts: A Versatile Toolkit for
           Heterocycle and Carbocycle Construction
    • Authors: Qing-Qing Cheng; Yang Yu, Julietta Yedoyan, Michael P. Doyle
      Abstract: Over the past decade, vinyldiazo compounds have provided mild, efficient, and highly selective methods for the construction of heterocycles and carbocycles. Dinitrogen extrusion with suitable catalysts provides the carbon framework for [3+n] cycloaddition with a large variety of dipolarophiles. This minireview, covering the latest achievements in the field of metal-catalyzed cyclization reactions with vinyldiazo reagents, focuses on reagent- or catalyst-dependent chemodivergence: different vinyldiazo reagents or metal catalysts direct reactions to different cyclization pathways that give different reaction outcomes. Accordingly, metal-catalyzed cyclization reactions of vinyldiazo compounds with nitrosoarenes, nitrones, indoles, and other diazo compounds are chosen to showcase the controllable versatility of the combination of vinyldiazo reagents and metal catalysts.Toolkit manual: This minireview covers the latest achievements in the field of metal-catalyzed cyclization reactions of vinyldiazo compounds, with emphasis on reagent- or catalyst-dependent chemodivergence, aiming to provide an illustrated manual of the versatile toolkit containing vinyldiazo reagents and metal catalysts for the construction of heterocycles and carbocycles.
      PubDate: 2018-01-02T08:51:04.494807-05:
      DOI: 10.1002/cctc.201701346
       
  • Front Cover: Mechanism of Carbon Monoxide Dissociation on a Cobalt
           Fischer–Tropsch Catalyst (ChemCatChem 1/2018)
    • Authors: Wei Chen; Bart Zijlstra, Ivo A. W. Filot, Robert Pestman, Emiel J. M. Hensen
      Pages: 1 - 1
      Abstract: The Front Cover refers to the complex mechanism underlying the dissociation of CO on a cobalt nanoparticle, a reaction pivotal to Fischer-Tropsch synthesis. In their Communication, W. Chen et al. probed the direct CO dissociation on Co catalysts using isotopic scrambling and in situ infrared spectroscopy, which led to the conclusion that CO dissociation does not require H atoms. More information can be found in the Communication by W. Chen et al. on page 136 in Issue 1, 2018 (
      DOI : 10.1002/cctc.201701203).
      PubDate: 2018-01-09T08:27:42.760269-05:
       
  • Cover Feature: Confining Gold Nanoclusters in Highly Defective Graphitic
           Layers To Enhance the Methanol Electrooxidation Reaction (ChemCatChem
           1/2018)
    • Authors: Zhe Mao; Haihua Hu, Rui Su, Peizhi Liu, Yixing Li, Wenting Zhang, Xiaoning Zhao, Junjie Guo, Pengfei Guan, Gaowu Qin, Xuefeng Zhang
      Pages: 2 - 2
      Abstract: The Cover Feature shows a gold nanocluster confined within a highly defective graphitic cage. In their Communication, Z. Mao et al. demonstrate that such a construction not only improves the conductivity, accelerating the penetration of ions and electrons during the electrocatalytic oxidation of methanol molecules, but also suppresses the chemical/thermal coarsening of gold clusters. More importantly, the atomic-scale Au/C interfaces contribute to a synergistic effect that enhances the activity as compared to other gold-based catalysts. More information can be found in the Communication by Z. Mao et al on page 141 in Issue 1, 2018 (
      DOI : 10.1002/cctc.201700895).
      PubDate: 2018-01-09T08:27:53.347441-05:
       
  • Cover Feature: Switching the Cofactor Specificity of an Imine Reductase
           (ChemCatChem 1/2018)
    • Authors: Niels Borlinghaus; Bettina M. Nestl
      Pages: 3 - 3
      Abstract: The Cover Feature shows the switch of the cofactor specificity of an imine reductase from NADPH to NADH. In their Full Paper, N. Borlinghaus and B. M. Nestl demonstrate that by applying the CSR-SALAD, a tool for engineering enzymatic nicotinamide cofactor preference, and enlarging the mutant library by further amino acid substitutions, the NAPDH coenzyme preference of the imine reductase from Myxococcus stipitatus can be engineered. The mutagenesis of the nicotinamide binding pocket resulted in variants with reversed specificity and recovered activity. More information can be found in the Full Paper by N. Borlinghaus and B. M. Nestl on page 183 in Issue 1, 2018 (
      DOI : 10.1002/cctc.201701194).
      PubDate: 2018-01-09T08:27:42.714323-05:
       
  • Cover Feature: Modular Polyoxometalate–Layered Double Hydroxides as
           Efficient Heterogeneous Sulfoxidation and Epoxidation Catalysts
           (ChemCatChem 1/2018)
    • Authors: Tengfei Li; Wei Zhang, Wei Chen, Haralampos N. Miras, Yu-Fei Song
      Pages: 4 - 4
      Abstract: The Cover Feature shows the efficient catalytic conversion of sulphides and olefins under mild conditions using a polyoxometalate based multicomponent composite material. In their Full Paper, T. Li, W. Zhang et al. exploited the cooperative effects introduced by the various components of the composite material to design a flexible and stable multifunctional catalytic system, which is an effective method for the manufacturing of catalytic systems tailored for specific processes. These results are expected to provide a deeper understanding of the cooperative effects and a guide for designing new multifunctional catalytic systems. More information can be found in the Full Paper by T. Li, W. Zhang et al. on page 188 in Issue 1, 2018 (
      DOI : 10.1002/cctc.201701056).
      PubDate: 2018-01-09T08:27:40.259904-05:
       
  • Mechanism of Carbon Monoxide Dissociation on a Cobalt
           Fischer–Tropsch Catalyst
    • Authors: Wei Chen; Bart Zijlstra, Ivo A. W. Filot, Robert Pestman, Emiel J. M. Hensen
      Pages: 5 - 5
      Abstract: The front cover artwork for issue 1/2018 is provided by the Laboratory of Inorganic Materials Chemistry at Eindhoven University of Technology in The Netherlands. The image refers to the complex mechanism underlying the dissociation of CO on a cobalt nanoparticle, a reaction pivotal to Fischer–Tropsch synthesis. The authors used isotopic scrambling and in situ infrared spectroscopy to shed new light on this old issue. See the Communication itself at https://doi.org/10.1002/cctc.201701203.“CO dissociation, a key reaction step in the Fischer–Tropsch (FT) reaction, is reversible.” This and more about the story behind the research featured on the front cover can be found in this issue's Cover Profile. Read the full text of the corresponding research at https://doi.org/10.1002/cctc.201701203.
      PubDate: 2018-01-09T08:27:47.473741-05:
      DOI: 10.1002/cctc.201701936
       
  • 10 Volumes of ChemCatChem, a Cross Section of Catalysis Research from
           ChemPubSoc Europe
    • Authors: Michael A. Rowan
      Pages: 6 - 8
      Abstract: Pump up the volume: The 10th volume is a prelude to the 10th anniversary. Let us see what we can do in 2018 to spice up your catalysis life!
      PubDate: 2018-01-05T07:05:22.374839-05:
      DOI: 10.1002/cctc.201701905
       
  • Structure Sensitive Scaling Relations: Adsorption Energies from Surface
           Site Stability
    • Authors: Luke T Roling; Frank Abild-Pedersen
      Abstract: The design of heterogeneous catalysts is accelerated by the identification of thermochemical reactivity descriptors, which enable the prediction of promising materials through efficient screening. Motivated by previous discoveries of linear scaling relations between the adsorption energies of related atoms and molecules, we present a new scaling between the adsorption energies of metal atoms and metal-adsorbate complexes, which can be used to directly predict catalytically relevant molecular adsorption energies. In contrast to existing models based on the coordination number of surface atoms alone, our model can predict adsorption energies with site-by-site resolution considering local structural effects and also has potential extensions to include contributions of neighboring metal identity in alloy systems. Integration of this scaling with a previously identified model for metal-metal interactions enables the accurate prediction of molecular adsorption energies on nanoparticles by performing only a small set of slab-based calculations.
      PubDate: 2017-12-31T21:50:41.885447-05:
      DOI: 10.1002/cctc.201701841
       
  • Photoelectrocatalytic synthesis of Hydrogen Peroxide by Molecular
           Copper-Porphyrin Supported on Titanium Dioxide Nanotubes
    • Authors: Dogukan Apaydin; Hathaichanok Seelajaroen, Orathip Pengsakul, Patchanita Thamyongkit, Niyazi Serdar Sariciftci, Julia Kunze-Liebhäuser, Engelbert Portenkirchner
      Abstract: We report on a self-assembled system comprising a molecular copper-porphyrin photoelectrocatalyst, 5-(4-carboxy-phenyl)-10,15,20-triphenylporphyrinatocopper(II) (CuTPP-COOH), covalently bound to self-organized, anodic titania nanotube arrays (TiO2 NTs) for photoelectrochemical reduction of oxygen. Visible light irradiation of the porphyrin-covered TiO2 NTs under cathodic polarization up to -0.3 V vs. Normal Hydrogen Electrode (NHE) photocatalytically produces H2O2 in pH neutral electrolyte, at room temperature and without need of sacrificial electron donors. The formation of H2O2 upon irradiation is proven and quantified by direct colorimetric detection using 4-nitrophenyl boronic acid (p-NPBA) as a reactant. This simple approach for the attachment of a small molecular catalyst to TiO2 NTs may ultimately allow for the preparation of a low-cost H2O2 evolving cathode for efficient photoelectrochemical energy storage under ambient conditions.
      PubDate: 2017-12-29T06:26:11.957446-05:
      DOI: 10.1002/cctc.201702055
       
  • Molybdenum Disulfide–Alumina/Nickel-Foam Catalyst with Enhanced Heat
           Transfer for Syngas Sulfur-Resistant Methanation
    • Authors: Zhenpu Lu; Hegui Zhang, Siyang Tang, Changjun Liu, Hairong Yue, Bin Liang
      Abstract: Sulfur-resistant CO methanation by using MoS2-based catalysts possesses potential to produce synthetic natural gas from the direct use of un-desulfurized syngas with a low H2/CO ratio in industry. However, hotspots raised in the high exothermic reaction lead to catalyst deactivation and an uncontrollable reactor temperature, both of which hinder industrial applications. A metal-structured MoS2-Al2O3/Ni-foam catalyst with stable MoS2 active species and high heat-transfer efficiency was synthesized to resist deactivation and to remove the heat of the reaction through a hydrothermal synthesis process. This catalyst exhibited superior activity and stability in the sulfur-resistant methanation of syngas and has potential applications in highly exothermic and endothermic reactions.Beat the heat: A MoS2-Al2O3/Ni-foam catalyst is successfully synthesized and is shown to exhibit high reactivity and sulfur-tolerant performance for the H2S-containing methanation of CO owing to cooperation of the highly stable MoS2 active species and the high heat-transfer efficiency of the metal-structured support.
      PubDate: 2017-12-29T05:16:15.997537-05:
      DOI: 10.1002/cctc.201701314
       
  • Three-Dimensionally Hierarchical Pt/C Nanocomposite with Ultra-High
           Dispersion of Pt Nanoparticles as a Highly Efficient Catalyst for
           Chemoselective Cinnamaldehyde Hydrogenation
    • Authors: Duo Hu; Wenqian Fan, Zhi Liu, Ling Li
      Abstract: A monolithic carbon-supported Pt nanocomposite with an interconnected three-dimensionally hierarchical porous carbon framework and ultra-high dispersion of Pt nanoparticles (Pt/3DHPC) is synthesized by using an effective “liquid phase impregnation template” strategy. The obtained Pt/3DHPC possesses rich mesoporosity and a low amount of oxygen-containing functional groups, which notably improve the accessible internal surface area of macropores, number of active Pt sites, and electron transfer ability. When used as a catalyst for the selective cinnamaldehyde (CMA) hydrogenation towards cinnamyl alcohol (CMO), Pt/3DHPC exhibits high CMA conversion (92.7 %) and CMO selectivity (91.1 %) at 1 h reaction time, and the corresponding activity (1553.7 h−1) greatly surpasses not only the single-sized mesoporous carbon and microporous activated carbon-supported counterparts but also the previously reported Pt catalysts dispersed on other forms of carbon. Furthermore, Pt/3DHPC can be reused at least fifteen times without pronounced decay owing to the strong interaction between Pt and carbon. The present work demonstrates the validity of multiscale control in carbon-supported Pt catalysts by overall consideration of the mass transportation, and the accessibility, quantity, and capability of active sites towards chemoselective hydrogenation of CMA, which is expected to be extended to other catalysis-related processes.Ultra-high dispersion of Pt nanoparticles: A 3D hierarchical porous Pt/C nanocomposite with ultra-high dispersion of Pt nanoparticles is synthesized by means of an effective multicomponent infiltration of polymethyl methacrylate templates. Pt nanoparticles are ultra-highly dispersed in the wall of the carbon scaffold and give rise to sufficient active sites for cinnamaldehyde hydrogenation.
      PubDate: 2017-12-29T05:15:51.906019-05:
      DOI: 10.1002/cctc.201701301
       
  • Iron(III) Amine Bis(phenolate) Complex Immobilized on Silica-Coated
           Magnetic Nanoparticles: A Highly Efficient Catalyst for the Oxidation of
           Alcohols and Sulfides
    • Authors: Touraj Karimpour; Elham Safaei, Babak Karimi, Yong-Ill Lee
      Abstract: We aimed to immobilize a complex of iron(III) amine bis(phenolate) on silica-coated magnetic nanoparticles as a new magnetically recoverable catalyst (Fe3O4@SiO2-APTES-FeLGDC). Both the chemical nature and the structure of catalyst were confirmed by using field-emission transmission electron microscopy, field-emission scanning electron microscopy, FTIR spectroscopy, thermogravimetric analysis, vibrating sample magnetometry, X-ray photoelectron spectroscopy, XRD, atomic absorption spectroscopy, and elemental analysis. This sustainable catalyst leads to the efficient oxidation of a wide range of alcohols and sulfides with excellent conversion and selectivity under a mild conditions to their corresponding oxidized products, acids (or ketones) and sulfoxides, respectively. Furthermore, the stability of the structure and morphology of our efficient recyclable system was investigated, and all of the data proved that the complex was anchored firmly to the magnetite nanoparticles.Magnetic attraction: A new magnetically recoverable, sustainable, economical, and environmentally friendly catalyst made from an earth-abundant metal (Fe) and amine bis(phenol) ligand is described for the highly efficient oxidation of alcohols to acids (ketones) and the selective oxidation of sulfides to sulfoxides.
      PubDate: 2017-12-29T05:10:49.255618-05:
      DOI: 10.1002/cctc.201701217
       
  • TiO2-carbon materials derived from hydrothermal carbonization of waste
           
    • Authors: Yusuf Osman Donar; Selva Bilge, Ali Sinag, Oleksii Pliekhov
      Abstract: In this paper, we present a green, low cost carbon material derived from waste biomass (hazelnut shell and olive residue) to fabricate a binary TiO2/carbon composite for improving the photocatalytic performance of TiO2 under visible light. Synthesis, characterization and photocatalytic applications of TiO2/carbon composite were performed. Hydrothermal carbonization was used to obtain carbon support materials. A series of TiO2/carbon composite materials from waste biomass based hydrochar, fullerene and carbon nanotube has been prepared for the comparison purposes. Photocatalytic performances of all composites were measured by comparing Methylene Blue (MB) removal rates. The results show that waste biomass based hydrochar/TiO2 composites possessed superior visible light photocatalytic activity comparing with high technology carbons/TiO2 composites such as fullerene and carbon nanotube. The enhanced photodegradation capacity could be ascribed to the delocalized furanic conjugated system and functional groups of HS-TiO2 and OR-TiO2 composites.
      PubDate: 2017-12-27T08:51:22.266997-05:
      DOI: 10.1002/cctc.201701405
       
  • Enantioselective Dihydroxylation of Alkenes Catalyzed by
           1,4-Bis(9-O-dihydroquinidinyl)phthalazine-Modified Binaphthyl–Osmium
           Nanoparticles
    • Authors: Jie Zhu; Xiao-Tao Sun, Xiao-Dong Wang, Lei Wu
      Abstract: A series of unprecedented binaphthyl–osmium nanoparticles (OsNPs) with chiral modifiers were applied in the heterogeneous asymmetric dihydroxylation of alkenes. A remarkable size effect of the OsNPs, depending on the density of the covalent organic shells, on the reactivity and enantioselectivity of the dihydroxylation reaction was revealed. Successful recycling of the OsNPs was also demonstrated and high reaction efficiency and enantioselectivity were maintained.Binaphthyl–osmium nanoparticles: The first enantioselective dihydroxylation of alkenes is achieved by using novel 1,4-bis(9-O-dihydroquinidinyl)phthalazine [(DHQD)2PHAL]-modified binaphthyl–osmium nanoparticles (OsNPs). These nanoparticles are also demonstrated to have a shell-density effect and can be recycled.
      PubDate: 2017-12-27T05:01:10.368643-05:
      DOI: 10.1002/cctc.201701368
       
  • Highly Dispersed Ultrafine Palladium Nanoparticles Enabled by
           Functionalized Porous Organic Polymer for Additive-free Dehydrogenation of
           Formic Acid
    • Authors: Caiyan Cui; Yujiao Tang, Muhammad Asad Ziaee, Ruihu Wang, Dongxu Tian
      Abstract: Formic acid (FA) is one of the most favorable chemical hydrogen storage materials for renewable energy transformation, the development of efficient heterogeneous catalysts for ultraclean H2 generation from FA in the absence of any alkalis or additives under mild conditions remains a major challenge. Here, we present a porous organic polymer containing triphenylamine (TPA) and 2,6-bis(1,2,3-triazol-4-yl)pyridyl (BTP) units (TB-POP). The ultrafine palladium nanoparticles (NPs) with an average size of 1.5±0.6 nm can be facilely generated using convenient methods, and are uniformly dispersed over TB-POP support. TPA and BTP units are homogeneously arranged in the host framework of TB-POP, they serve as effective alternatives of basic sites to deprotonate FA into formate intermediates. Pd@TB-POP has demonstrated remarkable catalytic activity and high selectivity in additive-free dehydrogenation of aqueous FA solution. The value of initial turnover frequency (TOF) at 50 oC is as high as 1344 h-1. In sharp contrast, the use of sodium formate as an additive in the catalytic system results in the decrement of catalytic activity. The ultrafine palladium NPs are effectively immobilized during dehydrogenation of FA, and no obvious aggregation of palladium NPs is observed after consecutive catalytic runs.
      PubDate: 2017-12-23T00:10:35.845957-05:
      DOI: 10.1002/cctc.201701805
       
  • Hydrothermally Stable Ruthenium–Zirconium–Tungsten Catalyst for
           Cellulose Hydrogenolysis to Polyols
    • Authors: Martin Lucas; Katarina Fabičovicová, Peter Claus
      Abstract: In this work, we describe a catalytic material based on a zirconium–tungsten oxide with ruthenium for the hydrogenolysis of microcrystalline cellulose under hydrothermal conditions. With these catalysts, polyols can be produced with high yields. High and stable polyol yields were also achieved in recycling tests. A catalyst with 4.5 wt % ruthenium in total achieved a carbon efficiency of almost 100 %. The prepared Zr-W oxide is mesoporous and largely stable under hydrothermal conditions (493 K and 65 bar hydrogen). Decomposition into the components ZrO2 and WO3 could be observed at temperatures of 1050 K in air.Hydrothermal cellulose hydrogenolysis: A catalytic material based on a zirconium–tungsten oxide with ruthenium is described for the hydrogenolysis of microcrystalline cellulose under hydrothermal conditions. With these catalysts, polyols can be produced with high yields.
      PubDate: 2017-12-22T06:48:47.331483-05:
      DOI: 10.1002/cctc.201701113
       
  • Synthesis of Polyoxymethylene Dimethyl Ethers from Dimethyl Ether Direct
           Oxidation over Carbon-Based Catalysts
    • Authors: Xiu-Juan Gao; Wen-Feng Wang, Ying-Ying Gu, Zhen-Zhou Zhang, Jun-Feng Zhang, Qing-De Zhang, Noritatsu Tsubaki, Yi-Zhuo Han, Yi-Sheng Tan
      Abstract: The synthesis of polyoxymethylene dimethyl ethers (DMMx) with a selectivity of 84.3 % by direct oxidation of dimethyl ether (DME) was realized over 30 %Ti(SO4)2/active carbon (AC) catalyst. This process also significantly promotes the growth of the C−O chain. The catalytic performances of Ti(SO4)2/AC and Ti(SO4)2/graphene (G) catalysts differ largely for DME oxidation reaction, although both AC and G are carbon materials. The carbonyl and hydroxyl groups on the surface of the carbon-based catalysts play an important role in DME direct oxidation to DMMx. Owing to the differences of surface structure and chemical properties of AC and G materials, the different interaction between the Ti(SO4)2 and supports remarkably affects the sulfate structures on the supports surface and leads to the large differences in the acid and redox properties of catalysts.Modified carbon underground: The synthesis of polyoxymethylene dimethyl ethers (DMMx) with a selectivity of 84.3 % by direct oxidation of dimethyl ether is realized over an active carbon catalyst modified with Ti(SO4)2.
      PubDate: 2017-12-21T10:55:37.127799-05:
      DOI: 10.1002/cctc.201701213
       
  • Homocoupling of Phenylboronic Acid using Atomically Dispersed Gold on
           Carbon Catalysts: Catalyst Evolution Before Reaction
    • Authors: Tanja Parmentier; Simon R Dawson, Grazia Malta, Li Lu, Thomas E Davies, Simon A. Kondrat, Simon J Freakley, Christopher J Kiely, Graham John Hutchings
      Abstract: Coupling reactions to form new C-C bonds are extensively used in industrial synthetic processes. Gold has been shown to be an active catalyst for such reactions however, conflicting reports exist as to whether cationic Au or metallic Au is acting as the active species. We prepared a heterogeneous catalyst consisting of atomically dispersed Au-Clx supported on carbon and showed this to be active in the homocoupling of phenylboronic acid to biphenyl. However; characterisation of the catalyst materials, even after just a short exposure time to the reactants, revealed rapid reduction and sintering of the Au species into larger metallic nanoparticles which we propose to be the true active species in this instance. This study suggests that if cationic Au is an active catalyst, it must be stabilised against reduction and agglomeration by either forming complexes which are more stable than common chlorides or by strongly anchoring them firmly onto alternative support materials; as in this case the carbon supported Au-Cl species were easily reduced.
      PubDate: 2017-12-21T09:10:29.736038-05:
      DOI: 10.1002/cctc.201701840
       
  • Colloidal Au catalyst preparation: selective removal of
           polyvinylpyrrolidone from active Au sites
    • Authors: Baira Donoeva; Petra E. de Jongh
      Abstract: Colloids with controlled dimensions, morphology and composition can be used to obtain supported metal catalysts with desired characteristics. Yet, removal of capping agents which block active metal sites in such catalysts can be challenging: mild methods often result in incomplete removal of capping agents, while harsher methods can cause change in particle size or morphology or cause metal segregation for bimetallic particles. Here we provide evidence that polyvinylpyrrolidone used as a stabilizing agent for gold colloids is present both on the metal and the support surface after colloid deposition on the TiO2 support. The polymer adsorbed on Au sites blocks their catalytic activity when it cannot be desorbed/decomposed under reaction conditions. Polyvinylpyrrolidone can be removed completely from the active gold surface of Au/TiO2 without particle growth using a number of mild treatment methods described in this work, despite only partial removal (~45%) of the stabilizer from the bulk of Au/TiO2. The remaining>50% of polyvinylpyrrolidone resides exclusively on the TiO2 support and has no effect on the optical properties and catalytic activity of gold nanoparticles. The treated catalysts demonstrate catalytic activity and selectivity similar to those of a catalyst prepared by impregnation. These findings are important for further advancing the preparation of well-defined supported catalysts using metal colloids.
      PubDate: 2017-12-21T08:40:39.736488-05:
      DOI: 10.1002/cctc.201701760
       
  • Porous Carbon Nanosheet-Supported Chiral Squaramide for Highly
           Enantioselective Friedel-Crafts Reaction
    • Authors: Liyuan Zhao; Xiaoze Bao, Qingtao Hu, Baomin Wang, An-Hui Lu
      Abstract: Porous carbon nanosheet (PCN) was used for the first time as a support to immobilize quinine-squramide catalyst for the asymmetric Friedel-Crafts addition of pyrazolones to isatin ketimines. Relying on its open structure with macroporous network as well as hydrophobicity, the PCN-supported catalyst presents comparable catalytic performance to its homogeneous catalyst, providing products with high yields and ee values of up to 90% and 99%, respectively. Recycling batch reactions together with a continuous flow process confirmed the stable activity of the catalyst.
      PubDate: 2017-12-21T04:03:39.512036-05:
      DOI: 10.1002/cctc.201701897
       
  • Understanding the Hydro-metathesis Reaction of 1-decene by Using
           Well-defined Silica Supported W, Mo, Ta Carbene/Carbyne Complexes
    • Authors: Aya Saidi; Manoja Samantaray, Mykyta Tretiakov, Santosh Kavitake, Jean-Marie Basset
      Abstract: Direct conversion of 1-decene to petroleum range alkanes was obtained using hydro-metathesis reaction. To understand this reaction we employed three different well-defined single site catalysts precursors; [(≡Si-O-)W(CH3)5] 1, [(≡Si-O-)Mo(≡CtBu)(CH2tBu)2] 2 and [(≡Si-O)Ta(=CHtBu)(CH2tBu)2] 3. We witnessed that in our conditions olefin metathesis/isomerization of 1-decene occurs much faster followed by reduction of the newly formed olefins rather than reduction of the 1-decene to decane, followed by metathesis of decane. We found that Mo-based catalyst favors 2+2 cycloaddition of 1-decene forming metallocarbene, followed by reduction of the newly formed olefins to alkanes. However, in the case of W and Ta-based catalysts, a rapid isomerization (migration) of the double bond followed by olefin metathesis and reduction of the newly formed olefins were observed. We witnessed that silica supported W catalyst precursor 1 and Mo catalyst precursor 2 are better catalysts for hydro-metathesis reaction with TONs of 818 and 808 than Ta-based catalyst 3 (TON of 334). This comparison of the catalysts provides us a better understanding that, if a catalyst is efficient in olefin metathesis reaction it would be a better catalyst for hydro-metathesis reaction.
      PubDate: 2017-12-21T03:08:07.717855-05:
      DOI: 10.1002/cctc.201701993
       
  • Mechanistic Aspects of Acrylic Acid Formation from CO2-Ethylene Coupling
           over Pd- and Ni-based Catalysts
    • Authors: Yuanhui Li; Zhen Liu, Ruihua Cheng, Boping Liu
      Abstract: The mechanism of catalytic conversion of CO2 and ethylene to acrylic acid has been investigated through DFT and DLPNO-CCSD(T) calculations. Four bidentate ligands (dmpe,dcpe,dtbpe and tmeda) were systematically studied in order to understand the different catalytic behavior of the Pd-based catalyst and the well-known Ni-based catalyst. The energy barrier of Pd-/Ni-catalyzed C-C coupling appears to increase with a larger steric hindrance of the ligand, while the barrier of the corresponding β-H elimination shows an opposite tendency. The barrier of C-C coupling is likely higher than the associated barrier of β-H elimination in both catalytic systems provided that the coordinated ligand is bulky enough. The palladium catalytic center is more effective than the nickel center during the C-C coupling and β-H elimination stages when bulky ligand is involved, while the nickel catalyst in turn performs better with small ligands. The palladium catalyst tends to be always superior to the nickel catalyst during the following hydrogen transfer to the O atom. In general, the diamine ligand (tmeda) is less efficient than the diphosphine ligands for both systems. In the absence of the auxiliaries, a novel chelating carbene ligand was proposed to be quite efficient for Pd-catalyzed C-C coupling with the lowest energy barrier. Two ligands (dcpm, dtbpm) showed relatively better performance towards the palladium-catalyzed acrylic acid formation reaction among all the investigated ligands.
      PubDate: 2017-12-20T23:05:50.57902-05:0
      DOI: 10.1002/cctc.201701763
       
  • Promoting Catalytic Oxygen Activation by Localized Surface Plasmon
           Resonance: Effect of Visible Light Pre-treatment and Bimetallic
           Interactions
    • Authors: Roong Jien Wong; Constantine Tsounis, Jason Scott, Gary K.-C. Low, Rose Amal
      Abstract: Visible light pre-treatment has been found to be capable of enhancing the catalytic oxygen activation on AuPt/TiO2 by up to seven times. Visible light pre-treatment exploits the localized surface plasmon resonance effect of Au to generate free electrons, which are transferred to the Pt active sites. The electron transfer was evident from a change in Pt speciation observed from X-ray photoelectron spectroscopy, showing the presence of PtO after visible light pre-treatment. Photoluminescence spectroscopy was used to reveal the bimetallic synergistic enhancement, as indicated by an overall decrease in the charge recombination rate. Further examination revealed that a good bimetallic interaction is necessary to achieve the enhancement by visible light pre-treatment. Weak bimetallic interaction, such as the occurrence of element segregation in the bimetallic alloy, inhibits electron transfer from the Au to the Pt and increases electron recombination rates, diminishing the degree to which visible light pre-treatment improves catalytic performance.Surface plasmon promotion: Visible light pre-treatment has been found to be capable of enhancing the catalytic oxygen (see figure; blue) activation on AuPt/TiO2 by up to seven times. Visible light pre-treatment exploits the localized surface plasmon resonance effect of Au (purple) to generate free electrons (yellow), which are transferred to the Pt (gray) active sites.
      PubDate: 2017-12-20T07:55:33.283812-05:
      DOI: 10.1002/cctc.201701238
       
  • Organosilica Nanotube Templates: One-Pot Synthesis of Carbon-Modified
           Polymeric Carbon Nitride Nanorods for Photocatalysis
    • Authors: Mei Li; Hua Wang, Xiaobo Li, Shengbo Zhang, Jinyu Han, Anthony F. Masters, Thomas Maschmeyer, Xiao Liu
      Abstract: Polymeric carbon nitride (PCN) nanorods with surface carbon modifications were prepared in a one-step procedure by using phenylene-bridged organosilica nanotubes as structure-directing templates. The carbon-modified PCN nanorods demonstrated enhanced activity in photocatalytic hydrogen production and the degradation of methyl orange relative to conventional bulk PCN and PCN nanorod templated from pure silica nanotube. The enhancement is attributed to the nanorod structure and the formation of carbon nitride carbon heterojunctions, which facilitate photogenerated charge separation and migration.Carbon on the wall: Polymeric carbon nitride (PCN) nanorods with surface carbon modifications, prepared in a one-step procedure by using phenylene-bridged organosilica nanotubes as structure-directing templates, are more active in photocatalytic hydrogen production and dye degradation than conventional PCN nanorods.
      PubDate: 2017-12-20T07:45:28.426425-05:
      DOI: 10.1002/cctc.201701245
       
  • Solvent-Promoted Regio- and Stereoselectivity in Ru-Catalyzed
           Hydrocarboxylation of Terminal Alkynes: A DFT Study
    • Authors: Bholanath Maity; Debasis Koley
      Abstract: DFT calculations at the M06L-D3(SMD)/LANL2TZ(f)/6-311+G(d,p)//M06L/LANL2DZ/6-31G(d)* level were performed to explore the mechanism, solvent effect, and origin of selectivity in the hydrocarboxylation of terminal alkynes catalyzed by (PCy3)2(CO)RuHCl. This catalytic system offers a unique example in which selectivity in enol-ester synthesis is controlled in presence of different solvent media under mild reaction conditions. In CH2Cl2 solvent the regioselective gem-enol-ester (Pg) was preferred, whereas stereoselective Z-enol-ester (PZ) was observed exclusively in THF medium. We have unraveled the complete catalytic mechanism involving the following steps: a) alkyne coordination with subsequent nucleophilic attack and, finally, b) product elimination leading to the Markovnikov product Pg in both solvent media. Herein, the rate-limiting nucleophilic attack step requires an activation barrier of 20.5 (21.0) kcal mol−1, which is 5.7 (5.6) kcal mol−1 lower than the crucial vinylidene formation step encountered for anti-Markovnikov addition. Interestingly, a new reaction avenue unfolds under explicit THF medium, in which the inherent coordinating nature of the solvent becomes effective in altering the product regioselectivity. Under such an event, a highly facile ligandassisted proton shuttle (LAPS) mechanism is propagated, leading to vinylidene complex 11A. This intriguing mechanistic scenario facilitates favorably furnishing the PZ product rather than the Pg isomer by 4.3 kcal mol−1.Solvent effects on selectivity: The product selectivity in the hydrocarboxylation of terminal alkynes in the presence of different solvent environments is explored by means of a theoretical approach. In CH2Cl2 medium, Markovnikov addition become facile, whereas in THF medium the anti-Markovnikov Z-product is preferred via a facile vinylidene intermediate.
      PubDate: 2017-12-19T13:16:40.601969-05:
      DOI: 10.1002/cctc.201701345
       
  • Insights into the Catalytic Activity of [Pd(NHC)(cin)Cl] (NHC=IPr, IPrCl,
           IPrBr) Complexes in the Suzuki–Miyaura Reaction
    • Authors: Frédéric Izquierdo; Caroline Zinser, Yury Minenkov, David B. Cordes, Alexandra M. Z. Slawin, Luigi Cavallo, Fady Nahra, Catherine S. J. Cazin, Steven P. Nolan
      Abstract: The influence of C4,5-halogenation on palladium N-heterocyclic carbene complexes and their activity in the Suzuki–Miyaura reaction were investigated. Two [Pd(NHC)(cin)Cl] complexes bearing IPrCl and IPrBr ligands (IPr=1,3-bis(2,6-diisopropyl-phenyl)imidazol-2-ylidene; cin=cinnamyl) were synthesized. After determining the electronic and steric properties of these ligands, their properties were compared to those of [Pd(IPr) (cin)Cl]. The three palladium complexes were studied by using DFT calculations to delineate their behavior in the activation step leading to the putative 12-electron active catalyst. Experimentally, their catalytic activity in the Suzuki–Miyaura reaction involving a wide range of coupling partners (30 entries) at low catalyst loading was studied.With or without a halogen: The catalytic activities of [Pd(NHC)(cin)Cl] (NHC=IPr, IPrCl, IPrBr; cin=cinnamyl) complexes are compared in the Suzuki–Miyaura cross-coupling reaction. The activation pathway involving these complexes is studied by DFT calculations, and their activities are extensively tested by using an operationally simple protocol.
      PubDate: 2017-12-19T13:16:06.062256-05:
      DOI: 10.1002/cctc.201701279
       
  • In-situ synthesis of Bi2O3 nanoparticles on ZnMeLDHs (Me:Al/Cr) frameworks
           for the photocatalytic O2 evolutions from water under solar-light
           activation
    • Authors: Gabriela Carja; Diana Gilea, Pegie Cool, Elena M. Seftel
      Abstract: A key target to boost solar-to-chemical conversion processes is to fabricate an efficient solar-light responsive photocatalyst. Herein, we report the in-situ synthesis of nanoparticles (NPs) of Bi2O3 directly on Zn-based layered double hydroxides (LDHs) framework. The in-situ synthesis of Bi2O3NPs is done at room temperature, is ligand-free and explores the ability of ZnMeLDHs to reconstruct its layered structure after calcination in Bi(NO3)3 aqueous solution. The in-situ formation of Bi2O3NPs on ZnMeLDHs is assessed by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and UV-Vis analysis (UV-Vis) and compared with the features of a corresponding Bi2O3/LDH prepared by conventional impregnation route. The rapid photocatalytic response of the Bi2O3NPs/ZnMeLDHs (Me:Al/Cr)heterostructures is confirmed in O2 generation from water under solar-light irradiation. The O2 rate increased by a factor of ~ 2 for the ZnCrLDH based catalysts as compared to that of the family of ZnAlLDH catalysts. Further, the presence of the bismuth phase and its nano-dimension leads to an increased efficiency for the in-situ prepared Bi2O3NPs/LDHs as compared to that of impregnated Bi2O3/LDH and the pristine LDHs.
      PubDate: 2017-12-19T08:30:22.696382-05:
      DOI: 10.1002/cctc.201701749
       
  • Using Mg-Al mixed oxide and reconstructed hydrotalcite as basic catalysts
           for aldol condensation of furfural and cyclohexanone
    • Authors: Oleg Kikhtyanin; David Kadlec, Romana Velvarská, David Kubička
      Abstract: This study presents results on aldol condensation of furfural and cyclohexanone in presence of Mg-Al hydrotalcite-derived materials as solid basic catalysts at reaction temperature from 25 to 90 °C and cyclohexanone to furfural molar ratio of 1-10. Mg-Al mixed oxide exhibited reasonable activity with furfural conversion of ca. 50% after 180 min of the reaction at T=90 °C. The activity of reconstructed hydrotalcite was much higher with furfural conversion close to 100% at short reaction times. In comparison with Mg-Al mixed oxide, the initial reaction rate has increased 30-50 times. At similar reaction conditions cyclohexanone self-condensation on HTC-derived catalysts could not compete with aldol condensation because the former reaction was inhibited by produced water. The change in CH/F molar ratio influenced both furfural conversion and product selectivity, higher furfural content in the reaction mixture favoured the second condensation step.
      PubDate: 2017-12-19T07:30:35.104377-05:
      DOI: 10.1002/cctc.201701880
       
  • Green synthesis of rhodium nanoparticles, catalytically active in benzene
           hydrogenation and 1-hexene hydroformylation
    • Authors: Waleed Alsalahi; Wlodzimierz Tylus, Anna Trzeciak
      Abstract: Rhodium nanoparticles (Rh NPs) were prepared according to a novel green methodology based on the reduction of Rh(acac)(CO)2 in water at 80 °C. The nanoparticles, obtained without the addition of a reducing agent, were stabilized by polyvinylpyrrolidone (PVP) or polyvinyl alcohol (PVA) polymers and characterized by TEM (transmission electron microscopy), XPS (X-ray photoelectron spectroscopy), and XRD (X-ray powder diffraction) methods. The excellent catalytic activity of these Rh NPs was evidenced in the hydrogenation of benzene to cyclohexane. In the presence of PPh3, Rh NPs formed a highly active system in the hydroformylation of 1-hexene. In this system, they acted as a source of soluble rhodium species.Rh NPs were also synthesized in water using Rh2(OAc)4 and RhCl3 as rhodium sources, and their catalytic activity was compared with that of the rhodium precursors.
      PubDate: 2017-12-19T04:03:40.637484-05:
      DOI: 10.1002/cctc.201701644
       
  • An overview on the recent strategies for the enantioselective synthesis of
           1,1-diarylalkanes, triarylmethanes and related molecules containing the
           diarylmethine stereocenter
    • Authors: Gautam Panda; Sankalan Mondal, Deblina Roy
      Abstract: Of late there has been an increase in the active pharmaceutical agents and various other molecules containing the 1, 1-diaryl stereocenter. This has led to the increase in the development of novel synthetic strategies for accessing molecules having this structural moiety. The current review describes the various synthetic methodologies for the enantioselective synthesis of 1,1-diarylethanes, triarylmethanes and related molecules having 1,1-diaryl stereogenic center that came up during 1995-2017. The prime focus of the review is on the formation of the 1,1-diarylmethine stereocenter either through the use of various enantioselective processes using chiral catalysts (the asymmetric catalytic approach) or through the use of chiral substrates and achiral catalysts. Resolution of racemic substrates is also followed for the synthesis of this chiral molecule but this approach is not covered in this review. Moreover, comparative discussions on the future aspects of the synthesis of these molecules with a short comparison of the different routes and possible areas of development are also dealt with.
      PubDate: 2017-12-19T03:00:41.877457-05:
      DOI: 10.1002/cctc.201701601
       
  • Conventional and New Materials for SCR NOx Catalytic Reduction
    • Authors: Yu Liu; Jong-Min Lee
      Abstract: It is important to minimize NOx pollutant released into the atmosphere due to the harmful environmental and health effects brought by NOx emission. Many techniques are available to reduce NOx emission, among of them, Selective Catalytic Reduction (SCR) is one of the most efficient techniques. Conventional SCR systems involve ammonia (NH3) or urea (CO(NH2)2) as a reducing reagent to reduce NOx to N2 and H2O at high temperatures 300-400 °C. Research on developing novel low-temperature catalysts (LTC) for SCR of NOx still remains of interest. This work reviewed and compared conventional SCR catalysts with newly emerging Metal-Organic-Frame (MOFs) materials as potential alternatives for SCR catalysts.
      PubDate: 2017-12-19T01:20:24.065518-05:
      DOI: 10.1002/cctc.201701414
       
  • Graphene Quantum Dots Modified Hexagonal Tubular Carbon Nitride for
           Visible-light Photocatalytic Hydrogen Evolution
    • Authors: baojiang jiang; yanting gao, feng hou, shan hu, baogang wu, ying wang, haiqiu zhang, honggang fu
      Abstract: Herein, graphene quantum dots were modified on hexagonal tubular carbon nitride to form a composite photocatalyst by freeze-dry technology. The composite material with typical porous structure and enhanced surface area exhibits an improved visible-light photocatalytic performance for hydrogen evolution. With an optimum loading amount of 0.15 wt.% GQDs, the efficiency of composite photocatalyst for hydrogen evolution is 112.1 μmol h-1, which is about 9 times higher than that of bulk carbon nitride. During the photocatalytic reaction, graphene quantum dots play a photosensitizer role, which can expand the visible-light respond of photocatalyst, and decrease its band gap. Meanwhile, graphene quantum dots also act as an electron reservoir to improve the separation efficiency of photoinduced electron-hole pairs. It is important the graphene quantum dots can also absorb the long wave light based on its upper transfer luminescence property, which also contribute to the utilization of visible-light. This finding demonstrates that the graphene quantum dot modification is a promising method to improve visible-light photocatalytic activities for traditional photocatalysts.
      PubDate: 2017-12-18T10:51:07.392348-05:
      DOI: 10.1002/cctc.201701823
       
  • Nanosheets/Mesopore Structured Co3O4@CMK-3 Composite as Electrocatalyst
           for Oxygen Reduction Reaction
    • Authors: Lang Gan; Mengran Wang, Langtao Hu, Jing Fang, Yanqing Lai, Jie Li
      Abstract: Exploring highly effective and low-cost non-noble metal electrocatalysts for oxygen reduction reactions (ORR) will have a significance impact on the area of fuel cells and metal-air batteries. In this manuscript, we report a facile, efficient and environmental friendly method to deposit transition metal oxide nanosheets (NSs) on the backbone of ordered mesoporous carbon (CMK-3) via pyrolysis of the metal-precursor@CMK-3. The optimized CMK-3 catalyst with a coating of Co3O4 NS possesses a high surface area of 2396 m2 g-1 and demonstrates an excellent electrocatalytic activity towards ORR in alkaline media, which is much better than other transition metal oxide@CMK-3 catalysts and other carbon material-based catalysts (such as carbon nanotubes). In addition, the as-prepared catalyst possesses comparable electrochemical performances, and even superior durability and higher tolerance to methanol compared with commercially available Pt/C, which can be ascribed to the distinctive structure of nanosheets/mesopore (NSs/MP), indicative of great potential in the application of metal-air batteries.
      PubDate: 2017-12-18T09:20:46.628088-05:
      DOI: 10.1002/cctc.201701822
       
  • Silica-Grafted Neodymium Catalysts for the Production of Ultra-High
           Molecular Weight 1,4-cis-Polyisoprene
    • Authors: Reiner Anwander; Erwan Le Roux, Yucang Liang
      Abstract: Supported neodymium-based Ziegler-type catalysts are obtained by grafting homoleptic methylaluminate Nd(AlMe4)3 onto high-surface silicas including periodic mesoporous silica MCM-41, SBA-15, and KIT-6. Low [Et2AlCl]-cocatalyst contents allow for the fabrication of polyisoprenes with ultra-high molecular weight (UHMWPI). The synthetic rubbers display molecular weights as high as 3×106 g mol-1, polydispersity indices (PDIs) as low as 1.2, and microstructures with 99% cis-stereospecificity. Combined analysis of the organolanthanide/silica hybrid materials by nitrogen physisorption, FTIR and MAS-NMR spectroscopy, as well as elemental(metal) analysis, assist in elucidating the intra-pore surface organometallic chemistry, and suggest the formation of unprecedented organolanthanide species.
      PubDate: 2017-12-18T09:20:28.578469-05:
      DOI: 10.1002/cctc.201701830
       
  • (Anilino)anthraquinone Nickel-Catalyzed Random Copolymerization of
           Norbornene and Ethylene
    • Authors: Hailong Cheng; Zhengguo Cai
      Abstract: Nickel complexes bearing an (anilino)anthraquinone ligand with different electron-donating substituents were synthesized and shown to have unique properties for the random copolymerization of norbornene with ethylene. The nickel catalysts exhibited high activity (380–750 kg mol−1 h−1) and thermal stability in the production of cyclic olefin copolymers (COCs). The norbornene content of the obtained COCs could be controlled over a wide range (63.7–92.2 mol %) by changing the comonomer concentration in the feed. The glass transition temperature value increased linearly from 182 to 322 °C as a function of the norbornene content regardless of the nickel complex used.A nickel for your thoughts: The random copolymerization of norbornene with ethylene is achieved by using (anilino)anthraquinone nickel catalysts with high activity and thermal stability to give cyclic olefin copolymers with a controlled norbornene content and a wide range of glass transition temperatures.
      PubDate: 2017-12-18T09:05:32.95638-05:0
      DOI: 10.1002/cctc.201701418
       
  • NMR Isotope Tracking Reveals Cascade Steps in Carbohydrate Conversion by
           Sn-Beta
    • Authors: Samuel G Elliot; Esben Taarning, Robert Madsen, Sebastian Meier
      Abstract: Quantitative isotope tracking studies were used to investigate the reaction pathways occurring for Sn-Beta catalyzed carbohydrate conversion to various alpha-hydroxy esters. Experimental insight into the conversion of pentoses was sought (i) by identifying pathways based on isotope patterns in the reaction products and (ii) through probing asymmetric isotope incorporation into products. The results indicate that reaction intermediates remain coordinated to the active site throughout the reaction cascades, regardless of the reaction pathway. A predominant transformation of the C1 carbohydrate position to the C3 position of methyl lactate resembles enzymatic glycolysis. Likewise, the majority of retro-aldol cleavage occurs from the carbohydrate in the ketose form, again resembling biological glycolysis. In addition, various side-activities are detected in Sn-Beta catalyzed carbohydrate conversion, including 5,1-hydride and 1,2-carbon shift reaction of the carbohydrates.
      PubDate: 2017-12-18T07:22:53.758927-05:
      DOI: 10.1002/cctc.201701861
       
  • Sol-Gel Entrapped Nitroxyl Radicals: Catalysts of Broad Scope
    • Authors: Rosaria Ciriminna; Valerica Pandarus, Francois Béland, Mario Pagliaro
      Abstract: Sol-gel entrapped TEMPO-like radicals, excellent supported molecular catalysts for the selective and clean alcohol oxidation, including the primary hydroxyl functions of cellulose. Could these materials reach widespread utilization for the synthesis of fine chemicals, bio-based building blocks and even carboxyl cellulose nanofibrils' This study offers a critical perspective.
      PubDate: 2017-12-18T05:03:40.097145-05:
      DOI: 10.1002/cctc.201701910
       
  • Multiple Functionalized Hyperbranched Polyethoxysiloxane Promotes Suzuki
           Coupling Asymmetric Transfer Hydrogenation One-Pot Enantioselective
           Organic Transformations
    • Authors: Genwei Zhang; Rui Liu, Yajie Chou, Yu Wang, Tanyu Cheng, Guohua Liu
      Abstract: Utilization of amphiphilic poly(ethylene glycol) monomethyl ether modified hyperbranched polyethoxysiloxane as a support for the construction of bifunctional heterogeneous catalysts enables a highly efficient catalytic system thanks to its amphiphilic nature in aqueous organic transformations. Herein, through a three-component self-assembly procedure, we incorporate palladium/phosphine and chiral ruthenium/diamine functionality within poly(ethylene glycol) monomethyl ether modified hyperbranched polyethoxysiloxane, fabricating a multiple functionalized polyethoxysiloxane based mesoporous material. Structural analyses and characterizations disclose that well-defined dual single-site active centers are distributed uniformly within monodisperse mesoporous silica nanoparticles. As a bifunctional heterogeneous catalyst, this material performs the one-pot enantioselective tandem reaction of Pd-catalyzed Suzuki cross-coupling and Ru-catalyzed asymmetric transfer hydrogenation, affording various chiral biaryl alcohols with high yields and up to 99 % enantioselectivity. Furthermore, the catalyst can be recovered and recycled eight times without loss of its catalytic activity, demonstrating the practicability of the preparation of optically pure biaryl alcohols in one-pot organic transformation.Tandem to biaryls: Self-templating assembly of palladium/phosphine- and chiral ruthenium/diamine-functionality within poly(ethylene glycol) monomethyl ether modified hyperbranched polyethoxysiloxane enables an efficient enantioselective tandem reaction of Pd-catalyzed Suzuki cross-coupling and Ru-catalyzed asymmetric transfer hydrogenation, affording various chiral biaryl alcohols.
      PubDate: 2017-12-18T04:58:20.623979-05:
      DOI: 10.1002/cctc.201701256
       
  • The strongBeta-CF3 shielding effect in HFIP and 100 other organic
           solvents revisited with 17O NMR
    • Authors: Annika Bernhardt; Harald Kelm, Frederic William Patureau
      Abstract: An 17O NMR survey of more than one hundred ubiquitous organic solvents and compounds is presented with D2O as reference, including some typical oxofluorinated solvents such as HFIP, TFE, TFA and others. A strong alternating alfa, beta-CF3-substituent chemical shifts effect was thus observed. This alternating deshielding-shielding effect is suspected of having a role in the exceptional properties of these oxofluorinated solvents, notably in oxidative cross-coupling reactions.
      PubDate: 2017-12-15T13:11:13.572069-05:
      DOI: 10.1002/cctc.201701721
       
  • Operando Spectroscopic Study of Dynamic Structure of Iron Oxide Catalysts
           during CO₂ Hydrogenation
    • Authors: Yulong Zhang; Donglong Fu, Xianglin Liu, Zhengpai Zhang, Chao Zhang, Bianfang Shi, Jing Xu, Yi-Fan Han
      Abstract: Understanding of dynamic structure of active sites is of paramount importance for rational design of industrial catalysts. This work revealed the structure evolution of iron active phases for CO₂ hydrogenation over iron-based catalysts. With a combination of operando Raman spectroscopy and X-ray Diffraction coupled with online gas chromatography, the panoramic structure evolution of iron oxides (α-Fe₂O₃ and γ-Fe₂O₃) during activation and CO₂ hydrogenation were elaborated, i.e. α-Fe₂O₃ (γ-Fe₂O₃)α-Fe₃O₄ (γ-Fe₃O₄)α-Fe (γ-Fe)χ-Fe₅C₂ (θ-Fe₃C). Both iron carbides showed high catalytic activities while χ-Fe₅C₂ exhibited higher selectivity to lower olefins but weaker chain growth probability than θ-Fe₃C.
      PubDate: 2017-12-15T07:10:33.945009-05:
      DOI: 10.1002/cctc.201701779
       
  • Hydrogenolysis of Amide Acetals and Iminium Esters
    • Authors: Renat Kadyrov
      Abstract: Amide acetals and iminium esters were hydrogenated into amines under very mild reaction conditions over common hydrogenation catalysts. This finding provides a new strategy for the selective reduction of amides. The synthetic utility of this approach was demonstrated by the selective reduction of amides bearing ester and nitrile groups.Get in gear: Amide acetals and iminium esters are hydrogenated into amines under very mild reaction conditions over common hydrogenation catalysts. Taking advantage of this approach and applying known procedures for the formation of amide acetals and iminium esters by O-alkylation of amides, a simple and general approach is now available for the highly selective conversion of amides into amines.
      PubDate: 2017-12-15T06:00:30.08219-05:0
      DOI: 10.1002/cctc.201701287
       
  • In Situ Prepared Flexible 3D Polymer Film Photocatalyst for Highly
           Selective Solar Fuel Production from CO2
    • Authors: Rajesh Kumar Yadav; Abhishek Kumar, Dolly Yadav, No-Joong Park, Jae Young Kim, Jin-Ook Baeg
      Abstract: The conversion of CO2 to valuable solar fuels by means of solar energy using metal-free flexible film photocatalysts is an appealing strategy. Here we demonstrate a three dimensional aromatic polymer (3DAP) derived from triptycene (TC) as a metal free, stable and highly efficient visible light responsive flexible film photocatalyst for selective solar fuel production from CO2. For this research work, the polymerization of TC by the Diels-Alder reaction is exploited for the first time as a new synthetic approach for the construction of three dimensional aromatic polymer photocatalyst. The visible-light harvesting ability, band gap suitability, high Brunauer-Emmett-Teller (BET) surface area and electron transfer capability via interconnecting 3D chain of 3DAP contribute to the excellent performance of the film photocatalyst compared to the corresponding TC ligand. This work provides important insights into the design of flexible polymer film photocatalyst for selective solar fuel formation from CO2 and is expected to trigger further interest in sustainable solar energy conversion applications such as tailorable and wearable devices.
      PubDate: 2017-12-15T04:51:39.034601-05:
      DOI: 10.1002/cctc.201701730
       
  • Iron Oxide Nanoclusters Incorporated into Iron Phthalocyanine as Highly
           Active Electrocatalysts for the Oxygen Reduction Reaction
    • Authors: Yi Cheng; Ji Liang, Jean-Pierre Veder, Meng Li, Shuangming Chen, Jian Pan, Li Song, Hui-Ming Cheng, Chang Liu, San Ping Jiang
      Abstract: Iron-nitrogen-carbon (Fe-N-C) composites have emerged as active and non-precious-metal electrocatalysts for the oxygen reduction reaction (ORR). Here, we developed a simple process to synthesize FeOx nanoclusters (NCs) incorporated with iron phthalocyanine (FePc) supported on graphene (FeOx/FePc) as highly active electrocatalysts for the ORR by a self-assembly method. The electrochemical activity of FeOx/FePc depends on the loading or size of the FeOx NCs. The best results are obtained on FeOx/FePc with 10 wt % FeOx NCs of a size of approximately 2 nm and a thickness of approximately 0.6 nm, which achieves a half-wave potential of 0.888 V and current density of 37.6 Ag−1 at 0.9 V (vs. the reversible hydrogen electrode). This is 50 mV higher than that of FePc supported on graphene and 64 mV higher than that of Pt/C in 0.1 m KOH solution at a catalyst loading of 0.1 mg cm−2. X-ray absorption spectroscopy and electrochemical cyclic voltammetry results indicate that the incorporated FeOx NCs interact with the active center of FePc, Fe−N4, to enhance the electron transition and reversibility of the FeIII/FeII redox couple and promote the kinetics of the ORR. We demonstrate that the nature of the active center of FePc (i.e., Fe−N4) is related closely to the activity of the FeIII/FeII redox couple.Size matters: We synthesize FeOx nanoclusters (NCs) incorporated with iron phthalocyanine (FePc) supported on graphene (FeOx/FePc) as highly active electrocatalysts for the oxygen reduction reaction by a self-assembly method. The electrochemical activity of FeOx/FePc depends on the loading or size of the FeOx NCs. The best results are obtained on FeOx/FePc with 10 wt % FeOx NCs of a size of approximately 2 nm and a thickness of approximately 0.6 nm.
      PubDate: 2017-12-15T04:44:48.222159-05:
      DOI: 10.1002/cctc.201701183
       
  • Ligands Modulate Reaction Pathway in the Hydrogenation of 4-Nitrophenol
           Catalyzed by Gold Nanoclusters
    • Authors: Ricca Rahman Nasaruddin; Tiankai Chen, Jingguo Li, Nirmal Goswami, Jiaguang Zhang, Ning Yan, Jianping Xie
      Abstract: Protective ligands are key components of ligand-protected metal nanoclusters (NCs), as they offer good stability and multiple functionalities to the metal NCs in solution. Herein, we demonstrated that the ligand landscape on the NC surface could also be used to modulate the catalytic active sites of metal NCs in solution thus to direct the catalytic reaction towards desirable products through a different pathway. We found that thiolate ligands, namely, p-mercaptobenzoic acid (p-MBA), in Au25(p-MBA)18 NCs could influence the reaction pathway in the catalytic hydrogenation of 4-nitrophenol in solution. In particular, the well-defined ligand structure of Au25(p-MBA)18 NCs in solution provided a unique environment for the coadsorption of two substrate molecules (4-nitrophenol) on the Au NC surface, and this ligand modulation could activate a reaction pathway involving the formation of azobenzene intermediates from the two adsorbed substrate molecules, which are missing in nanogold catalysts without protective ligands. The discovery of this alternative reaction pathway highlights the importance of ligands on nanogold catalysts in modulating their active sites and directing their catalytic reaction pathways in solution and provides good opportunities to tailor the selectivity of ligand-protected metal NC catalysts.The road less traveled: We demonstrate that the ligand landscape on a nanocluster (NC) surface can be used to modulate the catalytic active sites of metal NCs in solution thus to direct the reaction towards desirable products through a pathway different from that commonly reported. We highlight the importance of ligands on nanogold catalysts to tailor the active site exposure and selectivity of ligand-protected metal NC catalysts.
      PubDate: 2017-12-15T04:01:15.573398-05:
      DOI: 10.1002/cctc.201701472
       
  • Enhancing Oxygen Storage Capability and Catalytic Activity of Lanthanum
           Oxysulfide (La2O2S) Nanocatalysts by Sodium and Iron/Sodium Doping
    • Authors: Shuai Tan; Dongmei Li
      Abstract: We report the enhanced oxygen storage capability (OSC) and activity of lanthanum oxysulfide (La2O2S) nanocatalysts, derived from the introduction of oxygen vacancies by sodium (Na) doping. Additionally, iron/sodium (Fe/Na) co-doping further increased the OSC by three times, with an additional 15–20 % increase in CO conversion for the water-gas shift (WGS) reaction, compared with the best CO conversion rate among Na-doped La2O2S catalysts. The significant enhancement in OSC and activity after Fe/Na co-doping may be attributed to the presence of Fe2+Fe3+ redox couple. Finally, the Fe/Na co-doped nanocatalyst alleviated the high temperature requirement of La2O2S catalysts without compromising stability.Enhanced oxygen storage capability (OSC) and activity of lanthanum oxysulfide (La2O2S) nanocatalysts, derived from the introduction of oxygen vacancies by sodium doping, is reported. Additionally, iron/sodium co-doping further increased the OSC by three times, with an additional 15–20 % increase in CO conversion for the water-gas shift reaction, compared with the best CO conversion rate among Na-doped La2O2S catalysts.
      PubDate: 2017-12-14T09:15:55.074043-05:
      DOI: 10.1002/cctc.201701117
       
  • Conductive Porous Network of Metal Organic Frameworks Derived
           Cobalt-Nitrogen-doped Carbon with the Assistance of Carbon Nanohorns as
           Electrocatalyst for Zinc-Air Battery
    • Authors: Jianshuo Zhang; Chuxin Wu, Meihua Huang, Yi Zhao, Jiaxin Li, Lunhui Guan
      Abstract: Herein, we report a new electrocatalyst for oxygen reduction reaction derived from bimetallic metal organic framework and single-walled carbon nanohorns. Due to the 3-D conductive network offered by the nanohorns, this type of catalysts exhibit comparable performance with the commercial 20% Pt/C catalyst as well as excellent durability and methanol tolerance at the half-cell test in an alkaline medium. Moreover, the new electrocatalyst shows higher peak power density (185 mW cm-2) than that of Pt/C catalyst (160 mW cm-2) in addition to a comparable stability in the real Zn-air battery test. A correlation between the value of the peak power densities and pore structures of some paralleled samples is studied in details.
      PubDate: 2017-12-13T23:08:29.437576-05:
      DOI: 10.1002/cctc.201701794
       
  • Photothermally Enhanced Plasmon-Driven Catalysis on Fe5C2@Au Core-Shell
           Nanostructures
    • Authors: Peng Miao; Wei Huang, Mansha Gao, Jiayu Chu, Bo Song, Ping Xu
      Abstract: Plasmon-driven catalysis has attracted great attention in recent years, while the reaction efficiency remains to be improved. Here, we demonstrate the fabrication of novel photothermal Fe5C2@Au core-shell nanostructures through a self-assembly process of Fe5C2 and Au nanoparticles (NPs) with the assistance of hexanethiol, which can be highly efficient surface enhanced Raman spectroscopy (SERS) platforms for the study of plasmon-driven dimerization of 4-aminothiophenol (4-ATP) and 4-nitrothiophenol (4-NTP). As compared to bare Au NPs, much accelerated reaction kinetics can be achieved on the Fe5C2@Au core-shell nanostructures by quantitatively determining the Raman intensity of the ν(N=N) band in the generated 4,4'-dimercaptobenzene (DMAB). The photothermal effect from the Fe5C2 NPs may lower the energy barrier and generate more "hot electrons" for the plasmon-driven catalysis. This photothermal route may open up new avenues for enhancing the reaction rate and broadening the research area of the plasmon-driven catalysis.
      PubDate: 2017-12-13T21:41:24.790487-05:
      DOI: 10.1002/cctc.201701901
       
  • The role of metallic copper in the selective hydrodeoxygenation of
           glycerol to 1,2-propanediol over Cu/ZrO2
    • Authors: Thomas Gabrysch; Baoxiang Peng, Sorin Bunea, Gerald Dyker, Martin Muhler
      Abstract: A series of Cu/ZrO2 catalysts with nominal CuO loadings of 5, 10, 18 and 31 wt.% was synthesized by co-precipitation, characterized and applied in the hydrodeoxygenation of glycerol under mild reaction conditions (200 °C, 25 bar H2). These catalysts were highly selective for the cleavage of C-O bonds while preserving C-C bonds leading to 95% selectivity to 1,2-propanediol. The conversion of glycerol was observed to be linearly correlated with the specific copper surface area derived from N2O frontal chromatography. The reaction was found to occur through the dehydration of glycerol to acetol followed by its hydrogenation to 1,2-propanediol. Metallic copper was identified as the active site for both reactions suggesting the acid ZrO2 sites to be blocked by water. Reusability studies showed that the catalyst was relatively stable and the conversion decreased by only 18% after three cycles.
      PubDate: 2017-12-13T11:05:26.945268-05:
      DOI: 10.1002/cctc.201701748
       
  • Intermediates in the Oxidative Degradation of a Ruthenium-Bound
           2,2′-Bipyridyl–Phenoxy Ligand during Catalytic Water Oxidation
    • Authors: Yingying Liu; Gui Chen, Shek-Man Yiu, Chun-Yuen Wong, Tai-Chu Lau
      Abstract: Water-oxidation catalysts (WOCs) based on transition-metal complexes often undergo oxidative degradation of the ligands, which leads to unidentifiable products. We report herein the use of a ruthenium(III) complex bearing a 2,2′-bipyridyl (bpy)–bis(phenoxy) ligand, [Ru(L)(pic)2]+ [1, H2L=6,6′-bis(2-hydroxyphenyl)-2,2′-bipyridine, pic=4-picoline] as a WOC. The phenoxy-type ligand in 1 is readily oxidized by CeIV in aqueous acidic medium to give a ruthenium bpy–dicarboxylate complex ([Ru(bda)(pic)2]+, H2bda=2,2′-bipyridine-6,6′-dicarboxylic acid) via ruthenium bpy–phenoxybenzoquinone (1′) and ruthenium bpy–bis(benzoquinone) (1′′) intermediates. All four ruthenium species can oxidize water; however, 1 and 1′ are rapidly oxidized to 1′′ by CeIV. On the other hand, 1′′ is robust enough that it is responsible for the initial phase of O2 evolution before it is finally oxidized to CO2 and [Ru(bda)(pic)2]+, which is a highly active WOC.Water oxidation: A water-oxidation catalyst bearing a Ru-bound 2,2′-bipyridyl (bpy)–phenoxy ligand is readily oxidized by CeIV to give Ru–bpy–dicarboxylate via Ru–1,2-benzoquinonephenoxy 4-phenoxy-1,2-benzoquinone intermediates.
      PubDate: 2017-12-13T09:10:27.610056-05:
      DOI: 10.1002/cctc.201701319
       
  • Hydrogen/Deuterium-Exchange Reactions of Methane with Aromatics and
           Cyclohexane Catalyzed by a Nanoscopic Aluminum Chlorofluoride
    • Authors: Beatriz Calvo; Thomas Braun, Erhard Kemnitz
      Abstract: H/D-exchange reactions between methane and deuterated solvents such as [D6]benzene and [D12]cyclohexane were heterogeneously catalyzed by nanoscopic aluminum chlorofluoride (ACF=AlClxF3−x, x≈0.05–0.3) under very mild conditions. 13C NMR spectroscopy experiments at labeled methane revealed the formation of all isotopologues. AlCl3, AlBr3, HS-AlF3, γ-Al2O3, and γ-Al2O3 preheated at 700 °C did not show any H/D-exchange reaction of methane or [D6]benzene. Mechanistically, electrophilic activation of methane was suggested at the ACF surface.Now available in H/D: Nanoscopic aluminum chlorofluoride (ACF) exhibits excellent catalytic activity in the H/D-exchange reaction of CH4 with deuterated arenes or cyclohexane that results from the interaction of strong Al Lewis acid centers and the reactants at the ACF surface.
      PubDate: 2017-12-13T07:40:47.338778-05:
      DOI: 10.1002/cctc.201701327
       
  • Improving the Thermodynamic Profiles of Potential Suzuki-Miyaura
           
    • Authors: Michael Busch; Matthew Davisson Wodrich, Clemence Corminboeuf
      Abstract: As a heavily used technique for forming new C-C bonds, developing new catalysts and reaction conditions for Suzuki-Miyaura cross-coupling reactions is highly desirable. Here, using molecular volcano plots, the influence of the electrophilic coupling component in catalytic cycle thermodynamics is revealed. Less reactive electrophiles, such as iodine, broaden the volcano plateau leading to a larger selection of catalysts having appealing thermodynamic profiles. On the other hand, fluorine and other more reactive electrophiles compress the volcano plateau, which shrinks the pool of catalysts having good thermodynamic profiles. As a result, judicious selection of the electrophile employed in a reaction may represent an appealing strategy for further tuning the thermodynamics of cross-coupling reactions.
      PubDate: 2017-12-13T06:35:59.23203-05:0
      DOI: 10.1002/cctc.201701710
       
  • Engineering Surface Structure of Binary/Ternary Ferrite Nanoparticles as
           High-Performance Electrocatalysts for Oxygen Evolution Reaction
    • Authors: Zhi-Ming Zhang; Pathik Pathik Sahoo, Jing-Bo Tan, Tong-Bu Lu, Shiva Kumar Singh
      Abstract: Cost-effective production of efficient and robust oxygen evolution electrocatalysts is primary importance in developing renewable energy technologies. Herein, we develop a simple and efficient method for exploring high-performance oxygen evolution reaction (OER) electrocatalysts by engineering the surface structure of ferrite nanoparticles on the carbon nanotube support via a reduction-engraved strategy. After the reduction treatment, abundant oxygen vacancies localized on the surface of the ultrafine ferrite nanoparticles favorably affect their electronic structure, assuring a rapid charge transfer, and expose more active sites. In 1.0 M KOH solution, the reduced composites exhibit superior OER electrocatalytic activity to IrO2, affording a current density of 10 mA cm−2 at overpotentials of merely 214 mV for Co0.5Ni0.5Fe2O4@o-MWCNT (r-CNFc), 221 mV for CoFe2O4@o-MWCNT (r-CFc) and 216 mV for NiFe2O4@o-MWCNT (r-NFc). It is worth mentioning that the r-CNFc could afford a current density of 100 mAcm−2 at an overpotential of 256 mV, which is ca.10 times higher than that of CNFc at the same overpotential(10.6 mA cm−2). These catalysts also exhibit long-term stability evaluated by controlled-current electrolysis at least for 120 h. These results demonstrate an efficient method for constructing high-performance and durable OER electrocatalysts by reducing mixed metal spinel oxides on the conductive support.
      PubDate: 2017-12-12T23:36:20.873506-05:
      DOI: 10.1002/cctc.201701790
       
  • Specific Inhibition of the Hydrogenolysis of Benzylic C−O Bonds Using
           Palladium Nanoparticles Supported on Nitrogen-Doped Carbon Nanofibers
    • Authors: Yukihiro Motoyama; Koshi Morii, Shoya Ishizuka, Sou Inomoto, Zhenzhong Zhang, Seong-Ho Yoon
      Abstract: Palladium nanoparticles supported on 5 %-nitrogen-doped, herringbone-type carbon nanofibers (Pd/N-CNF-H), which are prepared by thermally decomposing [Pd2(dba)3⋅CHCl3] (dba=dibenzylideneacetone) in toluene in the presence of N-CNF-H, were found to be an efficient catalyst for the chemoselective hydrogenation of alkenyl and nitro moieties in benzyl-protected alcohols and carboxylic acid derivatives with high turnover frequencies: the hydrogenation reactions of these functional groups proceeded smoothly even at ambient temperature under atmospheric H2 pressure, and the benzyl protecting groups in the molecules remained intact. Moreover, the recovered Pd/N-CNF-H catalyst could be reused without loss of its catalytic activity or chemoselectivity. The Pd/N-CNF-H catalyst also acted as an effective hydrogenation catalyst for the reduction of aromatic ketones to the corresponding benzyl alcohol derivatives with good to high product selectivity.Situation: immobilized: The catalytic activity of palladium nanoparticles towards hydrogenolytic cleavage of benzylic C−O bonds is effectively eliminated by immobilizing on nitrogen-doped, herringbone-type carbon nanofibers. The result is a chemoselective catalyst for the hydrogenation of alkenyl and nitro functionalities that is highly tolerant to benzyl protecting groups present in molecules.
      PubDate: 2017-12-12T09:05:42.827299-05:
      DOI: 10.1002/cctc.201701326
       
  • Catalytic Transfer Hydrogenation of Furfural to Furfuryl Alcohol with
           Recyclable Al–Zr@Fe Mixed Oxides
    • Authors: Jian He; Hu Li, Anders Riisager, Song Yang
      Abstract: A series of magnetic, acid/base bifunctional Al–Zr@Fe3O4 catalysts were successfully prepared by a facile coprecipitation method and utilized in the catalytic transfer hydrogenation (CTH) of furfural to furfuryl alcohol with 2-propanol as hydrogen source. The physicochemical properties and morphologies of the as-prepared catalysts were characterized by various techniques, including XRD analysis, N2 physisorption, vibrating sample magnetometry, thermal gravimetry analysis, X-ray fluorescence spectroscopy, NH3/CO2 temperature-programmed desorption, SEM, and TEM. The Al7Zr3@Fe3O4(1/1) catalyst with a Al3+/Zr4+/Fe3O4 molar ratio of 21:9:3 was found to exhibit a high furfuryl alcohol yield of 90.5 % in the CTH from furfural at 180 °C after 4 h with a comparatively low activation energy of 45.3 kJ mol−1, as calculated from the Arrhenius equation. Moreover, leaching and recyclability tests confirmed Al7Zr3@Fe3O4(1/1) to function as a heterogeneous catalyst that could be reused for at least five consecutive reaction runs without significant loss of catalytic activity after simple recovery by an external magnet. Notably, the catalyst proved also efficient for hydrogenation of other biomass-derived furanic aldehydes.Magnetic hydrogenation: The bifunctional Al–Zr@Fe3O4 catalyst shows excellent catalytic performance in the catalytic transfer hydrogenation of furfural and other biomass-derived furanic aldehydes using alcohol as hydrogen donor and offers facile reuse in consecutive reactions after its easy recovery by an external magnet.
      PubDate: 2017-12-12T08:21:29.077014-05:
      DOI: 10.1002/cctc.201701266
       
  • Development of visible light response of CeO2-x with the high content of
           Ce3+ and its photocatalytic property
    • Authors: Sàisài Yuán; Bin Xu, Qitao Zhang, Sixiao Liu, Ju Xie, Ming Zhang, Teruhisa Ohno
      Abstract: Photocatalysts that are responsive to visible light are necessary to utilize solar. We prepared a reduced CeO2-x with absorption in the visible region by a simple solvothermal method. A new absorption peak appeared around 500 nm (SPR), which is the origin of Ce3+. To elucidate the relationship between the Ce3+ and activity, decomposition of isopropyl alcohol (IPA) to generate acetone has been carried out under visible light irradiation. CeO2-x showed superior activity than that of pure CeO2. Ce3+ can induce oxygen vacancies in the lattice of CeO2-x, resulting in improvement of activity. In addition, the introduction of Ce3+ resulted in improvement of absorption of CeO2-x in the visible light region. Also, the appearance of small tentacles (Confeito-like) on the surface of CeO2-x not only provided more active sites but also prevented aggregation. Owing to its visible light responsiveness and its unique morphology, the performance of the material has been significantly improved.
      PubDate: 2017-12-11T22:20:44.153355-05:
      DOI: 10.1002/cctc.201701767
       
  • Oxygen Reduction Reaction on Ag(111) in Alkaline Solution: A Combined
           Density Functional Theory and Kinetic Monte Carlo Study
    • Authors: Shizhong Liu; Michael G. White, Ping Liu
      Abstract: We reported a detailed mechanistic study of the oxygen reduction reaction (ORR) on the model Ag(111) surface in alkaline solution by using density functional theory (DFT) and Kinetic Monte Carlo (KMC) simulations, where multiple pathways via either 2e- or 4e- mechanisms were included. The theoretical modelling presented is able to reproduce the experimentally measured polarization curves in both low and high potential regions. An electrochemical 4e- network including both chemisorbed water (*H2O)-mediated 4e- associative pathway and the conventional associative pathway was identified to dominate the ORR mechanism. On the basis of the mechanistic understanding derived from these calculations, the ways to promote the ORR on Ag(111) were provided, including facilitating *OH removal, **O2 reduction by *H2O, and suppressing **O2 desorption. Finally, the origin of different ORR behaviors between Ag(111) and Pt(111) was also discussed in detail.
      PubDate: 2017-12-11T14:50:51.079281-05:
      DOI: 10.1002/cctc.201701539
       
  • Solid Molecular Frustrated Lewis Pairs in a Polyamine Organic Framework
           for the Catalytic Metal-free Hydrogenation of Alkenes
    • Authors: Marcus Rose; Andrea Willms, Hannah Schumacher, Tarnuma Tabassum, Long Qi, Susannah L. Scott, Peter J. C. Hausoul
      Abstract: We report for the first time a metal-free heterogeneously catalyzed hydrogenation using a semi-solid frustrated Lewis pair (FLP). The catalyst consists of a solid polyamine organic framework and molecular tris(pentafluorophenyl)borane (BCF) that form a semi-immobilized FLP in situ in the catalytic hydrogenation of diethyl benzylidenemalonate. 11B NMR spectroscopy proves the successful hydrogen activation by the FLP. Furthermore, the B N interactions between the polyamine and BCF are investigated by IR and solid state NMR spectroscopy. The FLP 1,4-diazabicyclo[2.2.2]octane (DABCO)/BCF, which combines the features of a FLP and a classical Lewis adduct, functions as molecular reference in both, catalysis and characterization. Furthermore, computational studies enable a better insight into the hydrogen activation through DABCO/BCF and polyamine/BCF.
      PubDate: 2017-12-11T09:51:03.331172-05:
      DOI: 10.1002/cctc.201701783
       
  • Hydrotalcite promoted by NaAlO2 as strongly basic catalysts with record
           activity in glycerol carbonate synthesis
    • Authors: Sreerangappa Ramesh; François Devred, Ludivine van den Biggelaar, Damien P. Debecker
      Abstract: A new type of highly basic catalysts is obtained by promoting Mg-Al layered double hydroxides with sodium aluminate. The Mg-Al mixed oxides obtained by the calcination of pristine hydrotalcites are poorly active in the synthesis of glycerol carbonate from glycerol and dimethylcarbonate. Pure sodium aluminate on the other hand is highly active in this reaction, but it is also highly corrosive, making its handling problematic. Remarkably, promoting hydrotalcites with low amount of sodium aluminate is sufficient to reach high yields. At 90°C, with 3 wt.% catalyst and with a DMC:glycerol ratio of 2:1, a glycerol conversion of 92% was achieved after 30 min over the 10 wt. % NaAlO2/hydrotalcite catalyst with almost 100% selectivity towards glycerol carbonate. The texture and the crystallinity of the catalysts were strongly affected by the addition of NaAlO2. Yet the high activity was clearly correlated with the boost in basicity brought about by sodium aluminate promotion. While pristine hydrotalcites possess only weak basic sites, the basicity of the catalysts increased drastically upon promotion with NaAlO2, both in amount and strength. Diffuse reflectance infra-red spectroscopy coupled with CO2 adsorption show the presence of surface carbonates arising from strongly basic sites. Importantly, our study demonstrates that these basic catalysts are truly heterogeneous, stable, and reusable.
      PubDate: 2017-12-11T09:21:00.479607-05:
      DOI: 10.1002/cctc.201701726
       
  • Immobilization of Molecular Catalysts for Enhanced Redox Catalysis
    • Authors: Shunichi Fukuzumi; Yong-Min Lee, Wonwoo Nam
      Abstract: In the homogenous phase, redox catalysts are often deactivated by bimolecular reactions. For example, the charge-separated state of photoredox catalysts decayed via bimolecular back electron transfer reactions between the charge-separated molecules to decrease the lifetimes of the catalytically active species. When photoredox catalysts are immobilized on solid supports, the lifetime of the charge-separated state was remarkably elongated to enhance the photocatalytic activity. Immobilization of photoredox catalysts on electrodes is required for photocurrent generation, leading to development of solar cells. Metal-oxygen intermediates, which are active for oxidation of various substrates including water oxidation, are also deactivated via bimolecular reactions to produce inactive forms such as dinuclear metal bis-μ-oxo complexes. Immobilization of metal complex catalysts on solid supports prohibits the bimolecular deactivation, enhancing the catalytic activity and stability. This minireview focuses on recent development of immobilization of both organic and inorganic molecular catalysts on various supports for enhancement of the catalytic activity, selectivity and stability in thermal and photoinduced redox reactions.
      PubDate: 2017-12-11T07:52:51.842862-05:
      DOI: 10.1002/cctc.201701786
       
  • Aprotic Lithium Air Batteries Tested in Ambient Air with High Performance
           and Low Cost Bi-functional Perovskite Catalyst
    • Authors: Junfang Cheng; Yuexing Jiang, Ming Zhang, Yu Sun, Lu Zou, Bo Chi, Jian Pu, Jian Li
      Abstract: Aprotic lithium air batteries (LABs) with remarkably high energy density are facing some challenges including insufficient cycle stability, high-cost for application and fuzzy understanding about the mechanism. Seeking high performance and low cost catalysts is one of the effective solutions to resolve these problems. In this paper, perovskite oxide La₀.₆Sr₀.₄CoO₃ (LSC) together with Fe and Mn doped materials La₀.₆Sr₀.₄Co₀.₂Fe₀.₈O₃ (LSCF) and La₀.₆Sr₀.₄Co₀.₂Mn₀.₈O₃ (LSCM) are prepared and applied as catalysts for LABs, which are studied mostly in pure oxygen atmosphere and rarely in ambiant air before. The results present that these catalysts are effective for LABs and LSCF can improve the capacity and cycle number to 6027 mAhg-1 and 156 at current density of 400 mAg-1 in ambient air. The reasons for performance degradation of LABs tested in ambient air are ducussed by EIS spectra and products analysis, which also clarify the improvement reason of LSCF catalyst.
      PubDate: 2017-12-11T05:51:48.844988-05:
      DOI: 10.1002/cctc.201701666
       
  • Recent Advances on Computational Investigations of N-Heterocyclic Carbene
           Catalyzed Cycloaddition/Annulation Reactions: Mechanism and Origin of
           Selectivities
    • Authors: Yang Wang; Donghui Wei, Wenjing Zhang
      Abstract: The developments of theoretical studies on NHC-catalyzed [n+2] (n=2, 3, 4) and other cycloaddition/annulation reactions have been summarized in this review. The detailed mechanisms, role of NHC, and origin of chemo- and stereoselectivity of these kinds of reactions were illustrated to provide valuable insights for rational design of new NHC-catalyzed cycloaddition/annulation reactions with high selectivities. Moreover, computational and theoretical methods commonly used were also mentioned to open the door for deep exploration of the general principle for NHC-catalyzed reactions within theoretical chemistry.Carbene catalyzed: The developments of theoretical studies on NHC-catalyzed [n+2] (n=2, 3, 4) and other cycloaddition/annulation reactions have been summarized in this review. The detailed mechanisms, role of NHC, and origin of chemo- and stereoselectivity of these kinds of reactions were illustrated.
      PubDate: 2017-12-11T05:25:33.372739-05:
      DOI: 10.1002/cctc.201701119
       
  • Semirational Engineering of the Naphthalene Dioxygenase from Pseudomonas
           sp. NCIB 9816-4 towards Selective Asymmetric Dihydroxylation
    • Authors: Julia M. Halder; Bettina M. Nestl, Bernhard Hauer
      Abstract: Enzyme-catalyzed asymmetric dihydroxylation is a powerful tool for the selective oxyfunctionalization of various organic compounds. By applying Rieske non-heme dioxygenases (ROs), molecular oxygen and a reduction equivalent are needed for the generation of vicinal cis-diols. We report a comprehensive mutagenesis study of the active site of the naphthalene dioxygenase from Pseudomonas sp. NCIB 9816-4 comprising 62 variants. We aimed to understand the important structure–function relationships by investigating different substituted arene substrates and the geometry of the active site. Introducing single-point mutations at positions F202, A206, V260, H295, F352, and L307 resulted in drastic shifts in the reaction specificity, regioselectivity, and stereoselectivity (≥90 %) while maintaining the residual activity towards the natural substrate naphthalene.Score double! By applying naphthalene dioxygenase from Pseudomonas sp. NCIB 9816-4, a representative of the multicomponent Rieske non-heme dioxygenases, a wide range of alkene motifs adjacent to an arene moiety are selectively mono- and dihydroxylated. The product distribution is strongly influenced by mutations introduced in the active site of the enzyme, which lead to shifts in reaction specificity, regioselectivity, and stereoselectivity.
      PubDate: 2017-12-11T05:23:47.969256-05:
      DOI: 10.1002/cctc.201701262
       
  • Phosphate Functionalization of CeO2–ZrO2 Solid Solutions for the
           Catalytic Formation of Dimethyl Carbonate from Methanol and Carbon Dioxide
           
    • Authors: Iuliia Prymak; Oleg Prymak, Junhui Wang, Venkata Narayana Kalevaru, Andreas Martin, Ursula Bentrup, Sebastian Wohlrab
      Abstract: Phosphate surface groups on CeO2–ZrO2 solid solutions were generated by treating Ce–Zr–hydroxide precursors with phosphoric acid. In the catalytic formation of dimethyl carbonate (DMC) from methanol and CO2, the performance of the P-modified samples was markedly affected relative to that of the unmodified ones: Phosphate treatment caused remarkable changes in the phase composition, acid–base properties, and the ability to form monodentate methoxy intermediates. The DMC yield (1.6 %) was successfully improved from 0.24 to 1.6 % by phosphate modification of CeO2–ZrO2 (Ce/Zr=4.7, P/Zr=0.13) and by performing the reaction at 170 °C and 6.5 MPa for 1 h.Drop the base: Esterification of CO2 with MeOH over phosphate-functionalized CeO2–ZrO2 solid solutions results in a yield of dimethyl carbonate (DMC) that is more than six times higher than that obtained with untreated mixed oxides. Changed surface properties of the phosphated catalysts lead to a decrease in moderate and strong basic sites and an increase in Lewis acidic sites, which are responsible for enhanced formation of reaction intermediates.
      PubDate: 2017-12-11T05:22:51.277095-05:
      DOI: 10.1002/cctc.201701105
       
  • Accessing d-Valine Synthesis by Improved Variants of Bacterial
           Cyclohexylamine Oxidase
    • Authors: Rui Gong; Peiyuan Yao, Xi Chen, Jinhui Feng, Qiaqing Wu, Peter C. K. Lau, Dunming Zhu
      Abstract: Chemoenzymatic deracemization was applied to prepare d-valine from racemic valine ethyl ester or l-valine ethyl ester in high yield (up to 95 %) with excellent optical purity (>99 % ee) by employing a newly evolved cyclohexylamine oxidase (CHAO) variant Y321I/M226T exhibiting catalytic efficiency that was 30 times higher than that of the wildtype CHAO. Interestingly, CHAO and its variants showed opposite enantioselectivity for valine ethyl ester and phenylalanine ethyl ester.Off to the races: Chemoenzymatic deracemization of d/l-valine ethyl ester and l-valine ethyl ester is applied to prepare d-valine in high yield with excellent optical purity by employing a cyclohexylamine oxidase (CHAO) mutant.
      PubDate: 2017-12-11T05:16:37.875307-05:
      DOI: 10.1002/cctc.201701229
       
  • Potassium as Structural Promoter for Fe/AC Catalyst: Unusual Effect of
           Component Deposition Order on Magnetite Particle Size and Catalytic
           Behavior in Fischer-Tropsch Synthesis
    • Authors: Oleg Eliseev; Petr Chernavskii, Galina Pankina, Ruslan Kazantsev
      Abstract: The structural and catalytic properties of nanosized Fe3O4 particles deposited on activated charcoal (AC) are drastically affected by the sequence of component deposition order. Preliminary alkalization of AC followed by Fe deposition leads to formation of small magnetite particles (modal size of 4 nm) with uniform distribution. This catalyst demonstrates much higher iron-time yield in FT synthesis than counterparts prepared by co-impregnation and sequential impregnation with reverse order of component deposition (Fe, then K). The catalysts were characterized by nitrogen adsorption, X-ray diffraction, transmission electron microscopy, temperature-programmed reduction in Ar/H2 and СО/Н2 flow and in situ magnetic measurements. After calcinations in argon catalysts contain iron predominantly in the form of magnetite with minor amount of hematite in some cases. Activation of the catalyst in the CO/H2 stream prior catalytic test leads to the formation of surface Hegg carbide Fe5C2. Spent catalysts contain considerable amount of magnetite presumably due to partial oxidation of carbide by water in the course of FT reaction.
      PubDate: 2017-12-10T21:52:17.135922-05:
      DOI: 10.1002/cctc.201701818
       
  • Highly dispersed bimetallic nanoparticles supported on titanium carbides
           for remarkable hydrogen release from hydrous hydrazine
    • Authors: Tong Liu; Qingtao Wang, Jingzhi Yuan, Xue Zhao, Guanhui Gao
      Abstract: Catalytic decomposition of hydrous hydrazine (N2H4·H2O) are considered as one of the promising candidate for fuel cell field, but the sluggish reaction kinetics dramatically impede their practical application. In this study, bimetallic RhNi nanoparticles are successfully anchored on titanium carbides (MXene) by one-step wet-chemical method, building a block for superior catalysts toward hydrous hydrazine (N2H4·H2O) decomposition applying for chemical hydrogen storage. The synthesized RhNi/MXene catalysts are characterized by XPS, TEM, STEM-HAADA and ICP-AES. Due to the particles size and synergistic effect, the Rh0.8Ni0.2/MXene nanocatalysts demonstrate 100% H2 selectivity, excellent durability, and high reaction kinetics with turnover frequency value of 857 h-1 toward N2H4 ·H2O decomposition in alkaline solution.
      PubDate: 2017-12-08T02:14:57.986755-05:
      DOI: 10.1002/cctc.201701633
       
  • The effect of KNO₃ modification on the performance of Cu-Mn oxide
           catalyst for enhanced soot combustion
    • Authors: Han Zhao; Xiaoxia Zhou, Weimin Huang, Linyu Pan, Min Wang, Qinru Li, Jianlin Shi, Hangrong Chen
      Abstract: Further enhanced catalytic activity and improved reusability were achieved by applying facile KNO3 modification on the synthesis process of a Cu-Mn mixed oxide (CuMnO). Upon KNO3 modification, the characteristic finishing temperature (Tf) of catalytic soot combustion successfully decreased from 360 oC for CuMnO to 338 oC for the K-modified product CuMnO(K). Moreover, this Tf value for CuMnO(K) remained amazingly low, at 346 oC, even after 5 runs of activity test. The excellent performance of CuMnO(K) is believed to be attributed to its well-dispersed nanoparticle morphology, which is totally different from the microspherical feature of CuMnO and is much beneficial for its sufficient contact with the soot particles. Additionally, an interesting phase evolution of CuMnO(K) was observed for the first time, from Cu1.5Mn1.5O4 to the mixed phases of CuO, K2Mn4O8 and MnOx during the consecutive test runs. And such mixed phases are believed to be responsible for the enhancement and stabilization of catalytic activity. Furthermore, the mechanism for the morphology transformation upon KNO3 modification and for the phase evolution during soot combustion was investigated.
      PubDate: 2017-12-07T11:06:01.444209-05:
      DOI: 10.1002/cctc.201701735
       
  • Synthetic & Catalytic Potential of Amorphous Mesoporous Aluminosilicates
           Prepared by Post-Synthetic Aluminations of Silica in Aqueous Media
    • Authors: Roel Locus; Danny Verboekend, Martin d'Halluin, Michiel Dusselier, Yuhe Liao, Nicolas Nuttens, Tony Jaumann, Steffen Oswald, Luis Mafra, Lars Giebeler, Bert Sels
      Abstract: Amorphous aluminosilicates catalysts have been used industrially on a large scale for almost a century. However, the influence of the pH on the alumination of silica in aqueous solutions has remained largely unclear. Herein, room temperature aluminations of different mesoporous amorphous silicas (fumed silica, dried silica gel, SBA-15, MCM-41, and COK-12) with aqueous solutions of various pH (3-13) are explored. The aqueous solutions are prepared using different aluminum sources (Al(NO3)3 or NaAlO2) and alkaline additives (NaOH or NH4OH). The decoupling of pH and Al source using alkaline additives results in a vast experimental potential to prepare unique aluminosilicates, where an important role is played by the pH development during the treatment. The bulk and surface composition, acidity, aluminum coordination, morphology, hydrothermal stability, and porosity of the obtained materials are characterized. Optimal samples possess large surface areas and superior acidities (up to 50% higher) and outstanding stabilities compared to aluminosilicates prepared via state of the art methods. The obtained materials are evaluated in a series of acid-catalyzed model reactions. The potential of the obtained materials is emphasized by the similar or superior acidity and catalytic performance compared to several benchmark industrial silica-alumina-based catalysts.
      PubDate: 2017-12-07T09:07:36.199239-05:
      DOI: 10.1002/cctc.201701660
       
  • Sandwich-Like Silica@Ni@Silica Multicore–Shell Catalyst for the
           Low-Temperature Dry Reforming of Methane: Confinement Effect Against
           Carbon Formation
    • Authors: Zhoufeng Bian; Sibudjing Kawi
      Abstract: We synthesize a new sandwich-like silica@Ni@silica multicore–shell catalyst. Firstly, Ni phyllosilicate (NiPS) is supported on silica nanospheres by a simple ammonia evaporation method. Then NiPS is coated with a layer of mesoporous silica to obtain a core–shell NiPS@silica structure by the hydrolysis of tetraethylorthosilicate (TEOS). The thickness of the shell can be tuned by varying the amount of TEOS. After calcination and H2 reduction at high temperature, multiple small Ni nanoparticles (≈6 nm) are generated and supported on the inner silica core but also encapsulated within the outer mesoporous silica shell. This silica@Ni@silica multicore–shell catalyst shows a high and stable conversion (≈60 %, gas hourly space velocity=60 000 mL h−1 gcat−1) for the dry reforming of methane (DRM) at 600 °C, whereas pristine NiPS deactivates quickly because of heavy carbon formation. We investigated the spent catalysts by using thermogravimetric analysis and TEM and found that there is almost no carbon formation for this new multicore–shell catalyst. Compared with a conventional Ni@silica core–shell catalyst, our multicore–shell catalyst is much easier to synthesize and the process does not require any toxic organic solvents. We believe that this strategy to make a multicore–shell catalyst can be applied to more nanomaterials and extended to other catalytic reactions besides DRM.Resistance is useful: A new sandwich-like silica@Ni@silica multicore–shell catalyst is prepared. This catalyst shows a stable catalytic performance and high carbon resistance for the low-temperature dry reforming of methane because of the confinement effect.
      PubDate: 2017-12-07T09:02:08.951356-05:
      DOI: 10.1002/cctc.201701024
       
  • Molybdenum Sulfide Nanosheet-Based Hollow Porous Flat Boxes and Nanotubes
           for Efficient Electrochemical Hydrogen Evolution
    • Authors: Liao Chen; Hongli Zhu
      Abstract: Intriguing amorphous/quasiamorphous molybdenum sulfide (MoSx) materials with active terminal disulfide S22− units have been recognized recently as prominent catalysts for the hydrogen evolution reaction (HER). Here, we diversify the MoSx morphologies and structures by a facile template-free solvothermal method to prepare fascinating MoSx nanosheet-based hollow porous flat boxes and nanotubes. As we increase the ethanol concentration in the mixed solvent for the reaction from 60 to 100 vol %, highly dispersed MoSx materials are obtained and the morphologies change from nanosheet to nanosheet-based hollow porous nanotubes and ultimately to nanosheet-based hollow porous flat boxes with the increasing S22− content. Catalytic measurements demonstrate that the hollow porous MoSx flat boxes and nanotubes have similar outstanding HER performances and can reach 10 mA cm−2 current at overpotentials of approximately 206 and 210 mV, respectively.Out of the box: We diversify MoSx morphologies and structures by a facile template-free solvothermal method to prepare fascinating MoSx nanosheet-based hollow porous flat boxes and nanotubes. Catalytic measurements demonstrate that the hollow porous MoSx flat boxes and nanotubes have similar outstanding performances for the hydrogen evolution reaction and can reach 10 mA cm−2 current at overpotentials of approximately 206 and 210 mV, respectively.
      PubDate: 2017-12-07T08:57:03.812803-05:
      DOI: 10.1002/cctc.201701306
       
  • First-Principles Computational Screening of Dopants to Improve the Deacon
           Process over RuO2
    • Authors: Zhen Yao; Karsten Reuter
      Abstract: Doping of metal oxides is a promising route to further optimize their catalytic performance. To guide corresponding experimental endeavors, we performed a DFT-based computational screening study for a wide range of metal dopant atoms in rutile RuO2. With a focus on the Deacon process, that is, the catalytic oxidation of HCl to chlorine and water, we used the rate-controlling Cl desorption energy as a reactivity descriptor. As stability descriptors, we employed the dopant surface segregation energy and as the dopant thermodynamic stability against precipitation into the metal oxide or bulk oxide grains. In the oxygen-rich conditions of the Deacon process, particularly the instability against oxide precipitation, represents a strong limitation. In this respect, doping with Cu appears as an optimum compromise between stability and catalytic activity enhancement.Dopants for rutile: A DFT-based computational screening study for a wide range of metal dopant atoms is performed to improve the catalytic oxidation of HCl to chlorine and water at rutile catalysts (Deacon process). Among the metals, Cu emerges as best compromise as it appears stable against precipitation into oxide grains under oxygen-rich conditions.
      PubDate: 2017-12-07T08:56:40.893154-05:
      DOI: 10.1002/cctc.201701313
       
  • On the Generality of Molecular Volcano Plots
    • Authors: Matthew Davisson Wodrich; Boodsarin Sawatlon, Michael Busch, Clemence Corminboeuf
      Abstract: In homogeneous catalysis, the structure and electronic configuration of the active catalysts can vary significantly. Changes in ligation, oxidation, and spin states have the potential to strongly influence the catalytic cycle energetics that, to a large degree, dictate catalytic performance. With the increased use of computational screening strategies aimed at identifying new catalysts, ambiguity surrounding structure/electronic configurations can be problematic, since it is unclear which species should be computed to determine a catalyst's properties. Here, we show that a single volcano plot constructed from linear free energy scaling relationships is able to account for variations in ligation, oxidation, and spin state. These linear scaling relationships can also be used to predict the free energies associated with a specific structure and electronic configuration of a catalyst based on a single descriptor. As a result, a single volcano plot can be used to rapidly screen for prospective new catalysts.
      PubDate: 2017-12-07T06:07:56.507714-05:
      DOI: 10.1002/cctc.201701709
       
  • Improving the Electrochemical Oxygen Reduction Activity of Manganese Oxide
           Nanosheets with Sulfurization-Induced Nanopores
    • Authors: Tianran Zhang; Xiaoming Ge, Zhao Zhang, Nguk Neng Tham, Zhaolin Liu, Adrian Fisher, Jim Yang Lee
      Abstract: Low-cost and high-activity electrocatalysts for the oxygen reduction reaction (ORR) are necessary for the development of fuel cells and metal-air batteries. Manganese oxide would be a good candidate because of its low cost, abundant supply, and environmental benignity if not for its relatively low activity compared with noble metals. To improve the ORR activity of manganese oxide, we developed a sulfurization process to create pores in 2 D manganese oxide nanosheets. The nanoporous MnO2 nanosheets (np-MnO2-ns) prepared as such contain 7 nm pores in the nanosheets and their half-wave potential (0.73 V) is 40 mV more positive than that of pore-free MnO2 nanosheets (0.69 V). The higher ORR activity of np-MnO2-ns may be attributed to the combination of a large surface area and the presence of high-ORR-activity Mn3+/4+ sites. The np-MnO2-ns also showed an enhanced oxygen evolution reaction activity and delivered a good performance in rechargeable Zn-air batteries.Punching pores: Sulfurization can be used to create nanopores in 2 D manganese oxide nanosheets. The as-prepared nanoporous manganese oxide nanosheets have a large surface area with many Mn3+/4+ sites, which are active for the oxygen reduction reaction, in the surface. They also have a good activity for the oxygen evolution reaction.
      PubDate: 2017-12-07T02:42:31.754665-05:
      DOI: 10.1002/cctc.201701192
       
  • Silica-Supported Molecular Catalysts for Tandem Reactions
    • Authors: Guohua Liu; Dongsong Zheng, Ronghua Jin, Rui Liu
      Abstract: The development of silica-supported molecular catalysts for tandem reactions is an important research direction of heterogeneous catalysis. Besides their significant merits in sustainable catalytic processes, numerous strategies have been utilized to construct silica-supported molecular catalysts. Here, we emphasize tandem reactions and summarize the recent advances in sequential organic transformations. This paper is composed of four parts. The beginning part introduces silicas as supports. The second part provides a large number of examples for the construction of non-chiral molecular catalysts used for tandem reactions. The third part offers an outline for the construction of chiral molecular catalysts used for enantioselective tandem reactions. Lastly, the perspectives for the further development of silica-supported molecular catalysts for tandem reactions are addressed.
      PubDate: 2017-12-06T22:12:38.394323-05:
      DOI: 10.1002/cctc.201701718
       
  • Facile synthesis of magnetic hierarchical core-shell structured
           Fe3O4@PDA-Pd@MOF nanocomposites: highly integrated multifunctional
           catalysts
    • Authors: Rong Ma; Pengbo Yang, Yao Ma, Fengling Bian
      Abstract: In this report, a novel magnetic hierarchical core-shell structured Fe3O4@PDA-Pd@[Cu3(btc)2] nanocomposite has been fabricated via a facile layer-by-layer assembly method, which contains a core of polydopamine (PDA) modified magnetic Fe3O4 nanoparticles (NPs), a transition layer of Pd NPs, and a porous outer shell of copper-based metal organic framework (MOF) with controllable thickness. This novel nanocomposite was characterized by TEM, FT-IR, XRD, XPS, N2 adsorption-desorption isotherm and VSM. The prepared Fe3O4@PDA-Pd@[Cu3(btc)2] (n=5) nanocomposite shows ultrahigh catalytic activity for the 4-nitrophenol reduction and Suzuki-Miyaura coupling reactions of aryl halides (Br, Cl) with arylboronic acids. Moreover, the nanocomposite also can be easily separated by an external magnet and reused at least 8 runs with excellent yields for both the reactions. The catalyst possesses outstanding catalytic performances mainly because the integration of [Cu3(btc)2] with Fe3O4@PDA-Pd that combines the advantages of each component could exhibit synergistic effect in our catalytic system. The facile synthesis strategy and brilliant catalytic performances of the Fe3O4@PDA-Pd@[Cu3(btc)2] (n=5) nanocomposite make it a promising catalyst for the practical application.
      PubDate: 2017-12-06T22:12:02.673925-05:
      DOI: 10.1002/cctc.201701693
       
  • Oxygen-Rich Carbon Quantum Dots as Catalysts for Selective Oxidation of
           Amines and Alcohols
    • Authors: Jianglin Ye; Kun Ni, Jie Liu, Guanxiong Chen, Mujtaba Ikram, Yanwu Zhu
      Abstract: Metal-free carbocatalysis has been widely utilized for aerobic oxidative reactions. Here, we report that oxygen-rich carbon quantum dots (O-CQDs) demonstrate a catalytic performance superior to graphene oxide, if used as a metal-free nanocatalyst for the direct transformation of amines and alcohols, under mild and solvent-free conditions. O-CQDs show a yield of 75 % for the oxidative coupling of amine to imine (with 5 wt % catalyst loading) and a conversion of 3.8 % for benzyl alcohol (with 2 wt % catalyst loading). The catalytic activities of thermally treated O-CQDs are further improved for benzylamine, for example, indicated by a yield of up to 98 % with 4 wt % catalyst loading. In addition, O-CQDs show a photoenhanced catalytic ability of amine (98 % yield with 5 wt % catalyst loading for 6 h reaction). Characterizations and simulations show that numerous carboxyl oxygen functional groups and unpaired electrons at the edge sites of O-CQDs are likely involved in the aerobic oxidation of amines.Oxygen-rich carbon quantum dots (O-CQDs) demonstrate superior homogeneous catalytic and photoenhanced catalytic performance, if used as a metal-free nanocatalyst for the direct transformation of amines and alcohols. Characterizations and simulations show that numerous carboxyl oxygen functional groups and unpaired electrons at the edge sites of O-CQDs are likely involved in the aerobic oxidation of amines.
      PubDate: 2017-12-06T09:01:36.301215-05:
      DOI: 10.1002/cctc.201701148
       
  • Modulation of Nitrile Hydratase Regioselectivity towards Dinitriles by
           Tailoring the Substrate Binding Pocket Residues
    • Authors: Zhongyi Cheng; Wenjing Cui, Yuanyuan Xia, Lukasz Peplowski, Michihiko Kobayashi, Zhemin Zhou
      Abstract: The regioselective hydration of dinitriles is one of the most attractive approaches to prepare ω-cyanocarboxamides or diamides and such regioselectivity is often beyond the capability of chemical catalysts. The use of nitrile hydratase to biotransform dinitriles selectively would be highly desirable. Molecular docking of two aliphatic dinitriles and two aromatic dinitriles into the active site of a nitrile hydratase (NHase) from Rhodococcus rhodochrous J1 allowed the identification of proximal NHase substrate binding pocket residues. Four residues (βLeu48, βPhe51, βTyr68, and βTrp72) were selected for single- and double-point mutations to modulate the NHase regioselectivity towards dinitriles. Several NHase mutants with an altered regioselectivity were obtained, and the best one was Y68T/W72Y. Docking experiments further indicated that the poor binding affinity of aliphatic and aromatic ω-cyanocarboxamides to the NHase variants resulted in distinct regioselectivity between wild-type and mutated NHases.Engineered enzymes: Nitrile hydratase from Rhodococcus rhodochrous J1 is able to catalyze α,ω-dinitrile into the corresponding final product, diamide. The introduction of Y68T/W72Y at the β subunit reverses the regioselectivity of nitrile hydratase towards dinitrile and results in the formation of the valuable cyanocarboxamide intermediate.
      PubDate: 2017-12-06T08:25:58.466544-05:
      DOI: 10.1002/cctc.201701170
       
  • Precisely Controlled Polymerization of Styrene and Conjugated Dienes by
           Group 3 Single-Site Catalysts
    • Authors: Jianming Huang; Zhaohe Liu, Dongmei Cui, Xinli Liu
      Abstract: This Review aims at a comprehensive overview on the recent stereospecific control polymerizations by group 3 metal complexes based catalytic systems in combination with aluminum alkyls and organoborates etc. co-catalysts. The involved monomers include styrene and substituted styrenes, and the conjugated dienes like isoprene and butadiene, and their derivatives. The syndio- and iso-selective polymerizations of styrene, unmasked polar styrenes and the copolymerizations of styrene with conjugated dienes and polar styrenes are summarized. The factors of influencing the catalytic activity and selectivity are discussed. The regio- and stereo- selective polymerizations of conjugated dienes, polar diene derivatives and their copolymerizations are reviewed. The relationship between catalyst structure and polymerization activity, the mechanism of stereo-selective polymerization and the influence of different cocatalysts are discussed.A solo performance: In this Review, a variety of group 3 single-site catalysts for the precise control of regio- and stereo- selective (co)polymerizations of styrene and conjugated dienes are systematically introduced. The activities, selectivities, molecular weights and molecular weight distributions dependent on the structure of the catalysts, cocatalysts, and reaction conditions etc. are detailed discussed.
      PubDate: 2017-12-05T09:45:52.155682-05:
      DOI: 10.1002/cctc.201701090
       
  • Metal–Organic Framework Mediated Synthesis of Small-Sized γ-Alumina as
           a Highly Active Catalyst for the Dehydration of Glycerol to Acrolein
    • Authors: Liang Huang; Feng Qin, Zhen Huang, Yan Zhuang, Jianxue Ma, Hualong Xu, Wei Shen
      Abstract: The dehydration of glycerol into acrolein was investigated over small-sized γ-Al2O3 prepared by a metal–organic framework (MOF) templated method. The particle size of alumina strongly affected the final physicochemical properties of γ-Al2O3 as well as its catalytic activity. The MOF-derived, small-sized γ-Al2O3 (M-Al2O3) catalyst exhibited higher stability and higher activity in the glycerol dehydration reaction than conventional bulk γ-Al2O3 and nanorod γ-Al2O3 owing to enriched intercrystal mesopores and an abundance of accessible acid sites. M-Al2O3 retained its high glycerol conversion (over 80 %) for nearly 200 h, whereas high acrolein selectivity (74 %) was achieved.Small talk: A nanosized γ-Al2O3 catalyst with enriched intercrystal mesopores is synthesized by the metal–organic framework template method. The enriched intercrystal mesopores and an abundance of accessible acid sites lead to significantly improved catalytic activity and stability in the glycerol dehydration reaction.
      PubDate: 2017-12-05T09:25:41.699158-05:
      DOI: 10.1002/cctc.201701061
       
  • Engineered Aminotransferase for the Production of d-Phenylalanine
           Derivatives Using Biocatalytic Cascades
    • Authors: Curtis J. W. Walton; Fabio Parmeggiani, Janet E. B. Barber, Jenna L. McCann, Nicholas J. Turner, Roberto A. Chica
      Abstract: d-Phenylalanine derivatives are valuable chiral building blocks for a wide range of pharmaceuticals. Here, we developed stereoinversion and deracemization biocatalytic cascades to synthesize d-phenylalanine derivatives that contain electron-donating or -withdrawing substituents of various sizes and at different positions on the phenyl ring with a high enantiomeric excess (90 to>99 % ee) from commercially available racemic mixtures or l-amino acids. These whole-cell systems couple Proteus mirabilis l-amino acid deaminase with an engineered aminotransferase that displays native-like activity towards d-phenylalanine, which we generated from Bacillus sp. YM-1 d-amino acid aminotransferase. Our cascades are applicable to preparative-scale synthesis and do not require cofactor-regeneration systems or chemical reducing agents.Couple up: d-Phenylalanine derivatives are valuable chiral building blocks for many pharmaceuticals. The development of an E. coli whole-cell system that couples Proteus mirabilis l-amino acid deaminase with an engineered aminotransferase that displays native-like activity towards d-phenylalanine allows the synthesis of these derivatives with high enantiomeric excess from commercially available racemic mixtures or l-amino acids.
      PubDate: 2017-12-05T09:21:04.94534-05:0
      DOI: 10.1002/cctc.201701068
       
  • The Highly Efficient Suzuki–Miyaura Cross-Coupling of (Hetero)aryl
           Chlorides and (Hetero)arylboronic Acids Catalyzed by
           “Bulky-yet-Flexible” Palladium–PEPPSI Complexes in Air
    • Authors: Jia-Sheng Ouyang; Yan-Fang Li, Fei-Dong Huang, Dong-Dong Lu, Feng-Shou Liu
      Abstract: A series of Pd–PEPPSI complexes were designed and synthesized. The relationship between catalyst structure and properties was systematically investigated. It was revealed that “bulky-yet-flexible” C3 bearing ancenaphthyl backbone was a highly efficient precatalyst and could be successfully employed in Suzuki–Miyaura reactions of (hetero)aryl chlorides with (hetero)arylboronic acids at a low palladium loading in the presence of a weak inorganic base in air.Bulking up: “Bulky-yet-flexible” Pd–PEPPSI complexes are developed and found to exhibit high reactivity for Suzuki–Miyaura cross-coupling reactions. A wide range of biologically relevant bi(hetero)aryls and poly(hetero)aryls are smoothly installed by using a low loading of the palladium catalyst, a weak base, and aerobic conditions. NHC=N-heterocyclic carbene.
      PubDate: 2017-12-05T09:20:58.600728-05:
      DOI: 10.1002/cctc.201701076
       
  • Bio-based α,ω functionalized hydrocarbons from multi-step reaction
           sequences with bio- and metallo-catalysts based on the fatty acid
           decarboxylase OleTJE
    • Authors: Samiro Bojarra; Dennis Reichert, Marius Grote, Álvaro Gómez Baraibar, Alexander Denning, Bernd Nidetzky, Carolin Mügge, Robert Kourist
      Abstract: OleT from Jeotgalicoccus sp. ATCC 8456 catalyzes the decarboxylation of ω-functionalized fatty acids to the corresponding alkenols, which can themselves serve as starting material for the synthesis of polymers and fine chemicals. To show the versatility of possible reactions, we developed a series of in vitro reaction cascades where an alkenol produced by the decarboxylation of ω hydroxy fatty acids can be further converted into alkenylamines and diols. By coupling OleT with an alcohol dehydrogenase or alcohol oxidase as well as an amino-transaminase, an oxidative decarboxylation followed by the oxidation of the terminal alcohol and a subsequent reductive transamination could be carried out. By using different cofactors or electron sources, the reactions could be performed sequentially or simultaneously. In addition, the combination of enzymatic decarboxylation with a ruthenium catalyst in a chemo-enzymatic cascade provides a novel way to synthesize long-chain diols.
      PubDate: 2017-12-05T08:36:29.30677-05:0
      DOI: 10.1002/cctc.201701804
       
  • Enzymatic Production of Non-Natural Nucleoside-5′-Monophosphates by a
           Thermostable Uracil Phosphoribosyltransferase
    • Authors: Jon del Arco; Javier Acosta, Humberto M. Pereira, Almudena Perona, Neratur K. Lokanath, Naoki Kunishima, Jesús Fernández-Lucas
      Abstract: The use of enzymes as biocatalysts applied to synthesis of modified nucleoside-5′-monophosphates (NMPs) is an interesting alternative to traditional multistep chemical methods which offers several advantages, such as stereo-, regio-, and enantioselectivity, simple downstream processing, and mild reaction conditions. Herein we report the recombinant expression, production, and purification of uracil phosphoribosyltransferase from Thermus themophilus HB8 (TtUPRT). The structure of TtUPRT has been determined by protein crystallography, and its substrate specificity and biochemical characteristics have been analyzed, providing new structural insights into the substrate-binding mode. Biochemical characterization of the recombinant protein indicates that the enzyme is a homotetramer, with activity and stability across a broad range of temperatures (50–80 °C), pH (5.5–9) and ionic strength (0–500 mm NaCl). Surprisingly, TtUPRT is able to recognize several 5 and 6-substituted pyrimidines as substrates. These experimental results suggest TtUPRT could be a valuable biocatalyst for the synthesis of modified NMPs.Stable in the face of heat: The enzymatic production of several modified nucleoside-5′-monophosphates is performed by uracil phosphoribosyltransferase from Thermus themophilus, TtUPRT. In addition, the functional and structural characterization of TtUPRT is reported for first time.
      PubDate: 2017-12-04T07:45:56.415608-05:
      DOI: 10.1002/cctc.201701223
       
  • Covalently Immobilized Lipase on a Thermoresponsive Polymer with an Upper
           Critical Solution Temperature as an Efficient and Recyclable Asymmetric
           Catalyst in Aqueous Media
    • Authors: Wuzong Zhou; Lan-lan Lou, Huaxin Qu, Wenjun Yu, Bei Wang, Lezi Ouyang, Shuangxi Liu
      Abstract: A thermoresponsive lipase catalyst with an upper critical solution temperature (UCST) of about 26 °C was exploited by covalent immobilization of an enzyme, Pseudomonas cepacia lipase (PSL), onto poly(acrylamide-co-acrylonitrile) via glutaraldehyde coupling. The experimental conditions for the PSL immobilization were optimized. The immobilized PSL was much more stable for wide ranges of temperature and pH than the free PSL. The material was also evaluated as an asymmetric catalyst in the kinetic resolution of racemic α-methylbenzyl butyrate at 55 °C in an aqueous medium and exhibited high catalytic performance and stability. Up to 50% conversion and 99.5% product enantiomeric excess were achieved, thus providing highly pure enantiomers. More importantly, this biocatalyst could be easily recovered by simple decantation for reuse based on temperature-induced precipitation. It showed good reusability and retained 80.5% of its original activity with a well reserved enantioselectivity in the 6th cycle. This work would shed light on the future development of new UCST-type enzyme catalysts.
      PubDate: 2017-12-03T21:51:01.95822-05:0
      DOI: 10.1002/cctc.201701512
       
  • Direct Synthesis of Hydrogen and Dimethoxylmethane from Methanol on
           Cu/SiO2 Catalysts with Optimal Cu+/Cu0 Sites
    • Authors: Chen Zhao; Liubi Wu, Bolong Li
      Abstract: Hydrogen is an important sustainable resource, and here we report a catalytic route for direct production of hydrogen (purity attains 95%) and dimethoxylmethane (DMM) from supercritical methanol over Cu/SiO2 catalysts at 240⁰C in a one-pot process. The procedure starts with methanol dehydrogenation to hydrogen and formaldehyde over the interface of Cu2O*SiO2 and Cu0 particle mixture, and subsequently the formaldehyde intermediate condenses with substantial methanol to form DMM in the liquid phase. The species of Cu0, CuO, or chrysocolla species are shown to be inactive for hydrogen generation from methanol, and the intrinsic active site for methanol decomposition is the Cu2O*SiO2/ Cu0 nanoparticles with interfaces, which is produced from hydrogen-reduction of Cu2Si2O5(OH)2 or from methanol reduction of Cu-O-Si moieties. A correlation between structure-activity on reduced Cu/SiO2 (prepared by deposition precipitation with ammonia) suggested that sole Cu0 was not active, but the combined Cu0 and Cu+ sites with interfaces on SiO2 with an optimal Cu+/Cu0 ratio of 1.56 were highly active for methanol dehydrogenation and subsequent condensation steps. The developed new catalytic system offers a facile and atom-economic way for generating pure hydrogen (almost carbon oxide free) from liquid methanol, which can be feasibly used into fuel cell and hydrogen involved biomass reactions.
      PubDate: 2017-12-03T21:50:45.241871-05:
      DOI: 10.1002/cctc.201701416
       
  • Enhanced Selectivity in the Hydrogenation of Anilines to Cycloaliphatic
           Primary Amines over Lithium-Modified Ru/CNT Catalysts
    • Authors: Patrick Tomkins; Thomas Ernst Müller
      Abstract: The hydrogenation of aromatic amines to the corresponding cycloaliphatic primary amines is an important industrial reaction. However, secondary amine formation and other side reactions are frequently observed resulting in reduced selectivity. The side-products are formed mostly on the support, yet support effects are little understood at present. This study describes the facile modification of Ru/CNT catalysts with LiOH, by this means significantly improving catalyst selectivity in toluidine hydrogenation without decreasing the activity of the catalysts. The effect is explained by LiOH diminishing acidic sites on the catalyst support and enhancing the adsorption of the aromatic ring on the metallic ruthenium nanoparticles. With the LiOH modified Ru/CNT catalyst also other substrates, such as methylnitrobenzenes, are converted efficiently. This study, thus, describes an improved catalyst for the preparation of cyclohexylamines and provides guidelines for future catalyst design.
      PubDate: 2017-12-02T10:01:38.253888-05:
      DOI: 10.1002/cctc.201701613
       
  • Whole-Cell Cascade Biotransformations for One-Pot Multistep Organic
           Synthesis
    • Authors: Shuke Wu; Zhi Li
      Abstract: Performing one-pot multi-catalysis reactions is a revolutionary tool for multistep synthesis, representing a fast-developing theme in catalysis field. To develop cascade reactions, enzymes are ideal catalysts due to their compatible reaction conditions. The implementation of enzyme cascades in recombinant microbial cells provides easily available self-replicating catalysts for facile one-pot biotransformations to produce a wide range of high-value (chiral) chemicals. In this minireview, we summarize the recent development of whole-cell cascade biotransformations according to the types of substrates, ranging from petrochemicals to biochemicals. Furthermore, we provide general instructions for the establishment of in vivo enzyme cascades, discuss the encountered problems and the corresponding solutions, and highlight the promising directions for future advance.
      PubDate: 2017-12-01T14:05:26.172096-05:
      DOI: 10.1002/cctc.201701669
       
  • The effect of copper loading on iron carbide formation and surface species
           in iron-based Fischer-Tropsch synthesis catalysts
    • Authors: Diego Zapata Pena; Lise Saue Jensen, Andrea Cognigni, Rune Myrstad, Thomas Neumayer, Wouter van Beek, Magnus Rønning
      Abstract: The effect of copper as promoter on iron carbide formation and the nature of surface species on iron-based catalyst during Fischer-Tropsch synthesis (FTS) have been investigated. Iron-based catalysts (15 wt% of Fe) supported on alumina promoted with copper (0, 0.6, 2 and 5 wt%) were characterised in situ at relevant FTS conditions. The catalysts promoted with 2 and 5 wt% of Cu showed higher catalytic activity due to the formation of Hägg carbide (Fe5C2) detected by in situ XANES and XRD. The carbide formation is attributed to a weakening of the iron-alumina mixed-compound interactions, and hence increasing iron reducibility and dispersion. The in situ XANES measurements indicated a maximum carburization degree (∼ 20-22 %) even at high Cu loading. The catalyst promoted with 5 wt% of Cu exhibited higher water-gas shift activity. Aliphatic hydrocarbons, formate and carboxylate species were detected on the catalyst surface during FTS. After exposing the spent catalysts to hydrogenation conditions, the carboxylate species remained strongly adsorbed while aliphatic hydrocarbons and formate species disappeared. The accumulation of oxygenates species on the catalyst surface increased with Cu loading. The interaction of oxygenates with alumina and iron oxide particles (FexOy) were revealed, with the latter being a possible reason for inhibition of further iron carburization.
      PubDate: 2017-12-01T11:06:09.840707-05:
      DOI: 10.1002/cctc.201701673
       
  • Tetrahedral Nickel(II) Phosphosilicate Single Site Selective Propane
           Dehydrogenation Catalyst
    • Authors: Guanghui Zhang; Ce Yang, Jeffrey T Miller
      Abstract: Silica-supported Ni catalysts usually show poor stability, low selectivity, and short lifetime in high-temperature alkane dehydrogenation reactions due to the reduction to Ni(0) nanoparticles under reaction conditions. Introduction of the phosphate ligand to the silica-supported Ni(II) provided single site tetrahedral Ni(II) phosphosilicate as a stable and selective propane dehydrogenation catalyst. The Ni(II)-OSi bonds activate C-H bonds of propane and make the Ni(II) sites catalytically active, while the Ni-OP bonds prevent the reduction of Ni(II) to Ni(0) under dehydrogenation conditions and help achieve high stability and selectivity.
      PubDate: 2017-12-01T02:05:37.633754-05:
      DOI: 10.1002/cctc.201701815
       
  • Catalytic Asymmetric Huisgen Alkyne–Azide Cycloaddition of Bisalkynes by
           Copper(I) Nanoparticles
    • Authors: Mu-Yi Chen; Zheng Xu, Li Chen, Tao Song, Zhan-Jiang Zheng, Jian Cao, Yu-Ming Cui, Li-Wen Xu
      Abstract: The use of chiral ligands to tune the reactivity and enantioselectivity of transition-metal catalyst for asymmetric transformations is a central challenge in synthetic organic chemistry. In this manuscript, chiral P-ligand (Tao-Phos)-assisted Cu2O-nanoparticles-catalyzed asymmetric azide–alkyne Huisgen cycloaddition is reported. The unique features of Tao-Phos were determined in the copper-catalyzed desymmetrization of pyrazolone-derived bisalkynes through catalytic asymmetric Huisgen [3+2] cycloaddition (CAHC). This CAHC transformation resulted in good yields with moderate to high enantioselectivities.When copper(I) nanoparticles meet chiral P ligand: Chiral P-ligand (Tao-Phos)-assisted Cu2O-nanoparticles-catalyzed desymmetrization of pyrazolone-derived bisalkynes provides good yields and high enantioselectivities (up to 90 % ee). The unique features of both Tao-Phos and CuI nanoparticles are revealed in the asymmetric copper-catalyzed azide–alkyne Huisgen cycloaddition.
      PubDate: 2017-11-30T05:16:11.5696-05:00
      DOI: 10.1002/cctc.201701336
       
  • Importance of the Reducing Agent in Direct Reductive Heck Reactions
    • Authors: Saeed Raoufmoghaddam; Subramaniyan Mannathan, Adriaan J. Minnaard, Johannes G. de Vries, Bas de Bruin, Joost N. H. Reek
      Abstract: The role of the reductant in the palladium N-heterocyclic carbene (NHC) catalyzed reductive Heck reaction and its effect on the mechanism of the reaction is reported. For the first time in this type of transformation, the palladium-NHC-catalyzed reductive Heck reaction was shown to proceed in the presence of LiOMe and iPrOH even at 10 °C to give the products very efficiently in excellent yields and with exceptional chemoselectivities. This study shows that the reaction proceeds through two distinct mechanisms that depend on the nature of the reducing agent. In the presence of a protic solvent or acidic medium the reaction undergoes protonation to yield the reduced product, whereas in the absence of proton source, it proceeds through the insertion of the reductant followed by reductive elimination. The kinetic data reveal that the oxidative addition is the rate-determining step in the reaction. The reaction profiles show first-order kinetics in aryl iodide and Pd and zero-order kinetics in LiOMe, benzylideneacetone, and the excess amount of NHC ligand. In addition, the reaction progress kinetic analysis shows that neither catalyst decomposition nor product inhibition occurs during the reaction. DFT calculations of the key steps confirm that the oxidative addition step is the rate-determining step in the reaction. Deuterium-labeling experiments indicate that the product is formed by the protonation of the Pd−Calkyl bond of the intermediate formed after enone insertion into the Pd−CAr bond. Application of chiral NHC ligands in the asymmetric reductive Heck reaction only results in poor enantioselectivities (enantiomeric excess up to 20 %) and is also substrate specific. DFT calculations suggest that the migration of the aryl group to the alkene of the substrate is the enantioselectivity-determining step of the reaction. It is further shown that if the steric bulk at the enone is small (a methyl group), the two transition state barriers from [PdII(L2)(ArI)(enone)] species Cre and Csi, which have the re and si face of the enone substrate coordinated to Pd, are very similar, in line with the experimental results. With a slightly larger group (an isopropyl substituent) a significant difference in energy barriers is calculated (2.6 kcal mol−1), and in the experiment this product is formed with a modest enantiomeric excess (up to 20 %).Double agent: The palladium N-heterocyclic carbene catalyzed reductive Heck reaction proceeds in the presence of LiOMe and iPrOH even at 10 °C to give the products very efficiently in excellent yields and with exceptional chemoselectivities. This study shows that the reaction proceeds through two distinct mechanisms that depend on the nature of the reducing agent.
      PubDate: 2017-11-30T05:15:35.134008-05:
      DOI: 10.1002/cctc.201701206
       
  • Telomerization of 1,3-Butadiene with Carbon Dioxide: A Highly Efficient
           Process for δ-Lactone Generation
    • Authors: João M. Balbino; Jairton Dupont, J. Carles Bayón
      Abstract: A very efficient and selective telomerization of 1,3-butadiene with CO2 that leads to the δ-lactone (3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one) was obtained using palladium acetate and tris(p-methoxyphenyl)phosphine as a catalyst in the presence of p-hydroquinone, N,N-diisopropylethylamine, and acetonitrile. A high turnover number of 4500 with 96 % selectivity to the δ-lactone was obtained after 5 h reaction at 70 °C. The reaction was deactivated by the presence of different 1,3-dialkylimidazolium ionic liquids, possibly by the formation of stable and inactive palladium-imidazole-2-ylidene carbenes.Terrific telomerization: A Pd catalyst with tris(p-methoxyphenyl)phosphine in the presence of p-hydroquinone, N,N-diisopropylethylamine, and acetonitrile is the best system for the telomerization of butadiene with CO2 reported to date.
      PubDate: 2017-11-30T05:15:26.314453-05:
      DOI: 10.1002/cctc.201701058
       
  • Phosphorus doped MoS2 nanosheets supported on carbon cloths as efficient
           hydrogen generation electrocatalysts
    • Authors: Luozhen Bian; Wei Gao, Jiamin Sun, Mingming Han, Fulin Li, Zhaofeng Gao, Lei Shu, Ning Han, Zai-xing Yang, Aimin Song, Yongquan Qu, Johnny C. Ho
      Abstract: Highly efficient and stable non-noble-metal electrocatalysts for hydrogen generation are desired for sustainable development of energy conversion and storage. Here, a facile low-temperature phosphidation process is developed for phosphorus doping into molybdenum disulfide (MoS2) nanosheets directly synthesized on carbon cloths to function as an integrated electrode for efficient hydrogen evolution reaction. As compared with the un-doped MoS2 nanosheets, the optimal phosphorus-doped (3.3 at%) MoS2 nanosheets exhibit the substantially lower overpotentials of 133 mV and 189 mV to drive the current densities of 20 mA cm-2 and 100 mA cm-2, respectively, with an impressive small Tafel slope of 67.0 mV dec-1. The excellent stability in acid media also guarantees the phosphorus-doped MoS2 nanosheet catalysts as promising candidates towards hydrogen generation for practical applications.
      PubDate: 2017-11-30T04:42:48.570645-05:
      DOI: 10.1002/cctc.201701680
       
  • Switching the Cofactor Specificity of an Imine Reductase
    • Authors: Niels Borlinghaus; Bettina M. Nestl
      Abstract: In the last years, imine reductases (IREDs) have gained importance for the formation of chiral amines by catalyzing asymmetric reductions of imines and chemo- and stereoselective reductive aminations. However, all characterized members of this steadily growing enzyme family demonstrated strict preference for NADPH, which entails reduced possibilities for efficient cofactor regenerations and limitations in the construction of whole cell systems. To alter the cofactor specificity from NADPH to NADH, we applied the “Cofactor Specificity Reversal—Structural Analysis and Library Design” (CSR-SALAD) mutagenesis strategy and enlarged the mutant library by further amino acid replacements. This engineering approach has been shown to result in IRED variants with up to 2900-fold improved NADH/NADPH specificity and completely recovered activity in the reduction of 2-methyl pyrroline (2MP).From NADPH to NADH: Variants of the R-selective imine reductase from Myxococcus stipitatus were identified, demonstrating a switched cofactor specificity. The utilization of CSR-SALAD combined with further engineering resulted in variants with up to 2900-fold improved cofactor preference for NADH and recovered activity.
      PubDate: 2017-11-29T09:26:16.549855-05:
      DOI: 10.1002/cctc.201701194
       
  • Synthesis of N-Heterocycles by Reductive Cyclization of Nitro Compounds
           using Formate Esters as Carbon Monoxide Surrogates
    • Authors: Dario Formenti; Francesco Ferretti, Fabio Ragaini
      Abstract: A series of alkyl and aryl formate esters were evaluated as CO sources in the Pd- and Pd/Ru-catalyzed reductive cyclization of substituted nitro compounds to afford heterocycles, especially indoles. Phenyl formate was found to be the most effective, and it allowed the desired products to be obtained in excellent yields, often higher than those previously reported with pressurized CO. Through detailed experiments and kinetic studies, we were able to discern between metal-catalyzed and base-mediated activation of phenyl formate and confirmed that just the base was effective in catalyzing its decarbonylation.Beat it! A very efficient and general protocol for the preparation of N-heterocycles (especially indoles) by using phenyl formate as a practical CO surrogate is demonstrated. The desired compounds are obtained in yields often higher than those previously reported by using gaseous CO. Mechanistic and kinetic analyses are successfully employed to clarify both the decarbonylation reaction of phenyl formate and the cyclization mechanism.
      PubDate: 2017-11-27T04:06:16.536511-05:
      DOI: 10.1002/cctc.201701214
       
  • Mechanism of Carbon Monoxide Dissociation on a Cobalt
           Fischer–Tropsch Catalyst
    • Authors: Wei Chen; Bart Zijlstra, Ivo A. W. Filot, Robert Pestman, Emiel J. M. Hensen
      Abstract: The way in which the triple bond in CO dissociates, a key reaction step in the Fischer–Tropsch (FT) reaction, is a subject of intense debate. Direct CO dissociation on a Co catalyst was probed by 12C16O/13C18O scrambling in the absence and presence of H2. The initial scrambling rate without H2 was significantly higher than the rate of CO consumption under CO hydrogenation conditions, which indicated that the surface contained sites sufficiently reactive to dissociate CO without the assistance of H atoms. Only a small fraction of the surface was involved in CO scrambling. The minor influence of CO scrambling and CO residence time on the partial pressure of H2 showed that CO dissociation was not affected by the presence of H2. The positive H2 reaction order was correlated to the fact that the hydrogenation of adsorbed C and O atoms was slower than CO dissociation. Temperature-programmed in situ IR spectroscopy underpinned the conclusion that CO dissociation does not require H atoms.Tough break: The mechanism of CO dissociation on Co Fischer–Tropsch catalysts has been long in debate. The present work sheds new light on this issue by using 12C16O/13C18O scrambling and in situ infrared spectroscopy.
      PubDate: 2017-11-23T05:30:38.695711-05:
      DOI: 10.1002/cctc.201701203
       
  • Facet-Selective Growth of Cadmium Sulfide Nanorods on Zinc Oxide
           Microrods: Intergrowth Effect for Improved Photocatalytic Performance
    • Authors: Xu Guo; Yubin Chen, Zhixiao Qin, Jinzhan Su, Liejin Guo
      Abstract: Well-designed architectures play an important role in accelerating charge transfer between the different components of hybrid photocatalysts. Herein, we report a simple one-step hydrothermal method to achieve a CdS/ZnO heterostructure with a novel spatial arrangement. The CdS nanorods were found to be attached to the surface of the ZnO microrods with an intimate face-to-face contact, and the heterointerfaces corresponded to {1 0 0} facets of CdS and {1 0 0} facets of ZnO. It was discovered that Zn(OH)2 intermediates were formed at first and then grew into hexagonal ZnO microrods through a solid–solid-phase transformation. Simultaneously, CdS nuclei grew to nanorods on the {1 0 0} facets of ZnO by oriented attachment during the one-step hydrothermal process. Under visible-light irradiation, obtained CdS/ZnO exhibited enhanced photocatalytic hydrogen generation owing to improved charge separation from the two-phase intergrowth effect. This work provides a facile hydrothermal route to construct intergrown heterostructures with desired spatial arrangements for improved photocatalytic properties.Hot rod: A simple one-step hydrothermal method to prepare the CdS/ZnO heterostructure with a novel spatial arrangement is reported. Under visible-light irradiation, CdS/ZnO exhibits enhanced photocatalytic hydrogen generation owing to improved charge separation from the two-phase intergrowth effect.
      PubDate: 2017-11-23T04:42:29.619482-05:
      DOI: 10.1002/cctc.201701078
       
  • Modular Polyoxometalate–Layered Double Hydroxides as Efficient
           Heterogeneous Sulfoxidation and Epoxidation Catalysts
    • Authors: Tengfei Li; Wei Zhang, Wei Chen, Haralampos N. Miras, Yu-Fei Song
      Abstract: The selective sulfoxidation of sulfides and the epoxidation of olefins are two types of important organic reactions, and the corresponding products of sulfoxides, sulfones and epoxides are used widely as raw materials in industrial processes. The fabrication of one efficient catalyst for both reactions remains a challenging task. We report the preparation of a highly efficient heterogeneous catalyst Mg3Al-ILs-La(PW11)2 using an exfoliation/assembly approach. The catalyst was characterised by FT-IR spectroscopy, XRD, thermogravimetric and differential thermal analysis, BET measurements, X-ray photoelectron spectroscopy, 29Si cross-polarisation magic-angle spinning NMR spectroscopy, 27Al magic-angle spinning NMR spectroscopy, SEM, high-resolution TEM, and energy-dispersive X-ray spectroscopy. The designed catalyst showed a high efficiency and selectivity for the sulfoxidation of sulfides and the epoxidation of olefins under mild conditions at a production rate of 208 and 31 mmol g−1 h−1, respectively. Moreover, Mg3Al-ILs-La(PW11)2 can be recycled and re-used at least five times without a clear decrease of its catalytic activity. The scaled-up experiments revealed that the catalyst retained its efficiency and robustness, which demonstrates the great potential of the catalyst for industrial applications.Going mild: The exploitation of an exfoliation/assembly design approach leads to the fabrication of an efficient heterogeneous catalyst for the selective sulfoxidation of sulfides and the epoxidation of olefins. Synergistic effects between the catalyst components lead to a high efficiency and selectivity for both types of reaction under mild conditions.
      PubDate: 2017-11-23T04:42:21.464925-05:
      DOI: 10.1002/cctc.201701056
       
  • Chemically Deposited Cobalt-Based Oxygen-Evolution Electrocatalysts on
           DOPA-Displaying Viruses
    • Authors: Jihun Rho; Sung Yul Lim, Inseong Hwang, Jeongse Yun, Taek Dong Chung
      Abstract: Filamentous bacteriophages were engineered to display 3,4-dihydroxy-l-phenylalanine (DOPA) onto which a cobalt oxide based oxygen-evolution catalyst (Co-OEC) spontaneously deposited at room temperature. Relative to the electrodeposited Co-OEC, the catalyst formed on the virus exhibited improved durability and current density in a small overpotential region, as well as decreased oxidation states for the formation of Co(OH)2, as confirmed by electrochemical and X-ray photoelectron spectroscopy analysis. Chemically deposited Co(OH)2 on the virus was oxidized to CoOOH during the water-oxidation process. Thus, the DOPA-displaying virus illustrates the affordability of a genetically engineered bacteriophage as a molecular support that can improve the catalytic performance of inorganic materials without any additional electrical energy.Time to split: Filamentous bacteriophages are genetically engineered to express DOPA on the surface of the major coat protein. A cobalt oxide based oxygen evolution catalyst (Co-OEC) is deposited onto the DOPA-displaying phages by simply immersing the phages in precursor solutions that contain Co2+. The oxygen evolution reaction activity of the Co-OEC-deposited phages is investigated by drop casting on the electrode.
      PubDate: 2017-11-23T04:40:34.445358-05:
      DOI: 10.1002/cctc.201701111
       
  • Selective Levulinic Acid Hydrogenation in the Presence of Hybrid
           Dendrimer-Based Catalysts. Part I: Monometallic
    • Authors: Anton L. Maximov; Anna V. Zolotukhina, Adila A. Mamedli, Leonid A. Kulikov, Edward A. Karakhanov
      Abstract: Hybrid Ru-containing catalysts, based on poly(propylene imine) (PPI) dendrimers, immobilized in silica pores, were synthesized and characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The synthesized Ru catalysts proved their efficiency in the selective hydrogenation of levulinic acid and its esters at 80 °C, 30 bar of H2, and 50 % volume substrate concentration in water. Quantitative yields of γ-valerolactone were obtained for both micro- and mesoporous Ru catalysts within 2 h with catalytic activity as high as 1610 h−1. The reaction rate and selectivity on γ-valerolactone were found to depend on several factors such as carrier structure, temperature, presence of water, and substrate/Ru ratio. The novelty of these hybrid materials is the presence of both weak acid (SiO2) and organic base centers (dendrimer amino groups), enhancing the dispersion of Ru nanoparticles. The presence of amino groups in the catalyst stabilizes the Ru nanoparticles during the synthesis and promotes the adsorption of levulinic acid on the surface of Ru nanoparticles during the reaction. Synthesized hybrid Ru catalysts can be reused several times without significant loss of activity.Dendrimer aid: Ru nanoparticle-based hybrid catalysts immobilized in dendrimer-modified silica pores promote the hydrogenation of levulinic acid and its esters under mild conditions. A mechanism for the reaction is suggested, which mostly proceeds through angelica lactone, not 4-hydroxyvaleric acid.
      PubDate: 2017-11-22T03:55:40.38162-05:0
      DOI: 10.1002/cctc.201700691
       
  • Palladium-Catalyzed Carbonylative Homocoupling of Aryl Iodides for the
           Synthesis of Symmetrical Diaryl Ketones with Formic Acid
    • Authors: Fu-Peng Wu; Jin-Bao Peng, Xinxin Qi, Xiao-Feng Wu
      Abstract: A convenient method for the palladium-catalyzed carbonylative homocoupling of aryl iodides was developed. With formic acid as the CO source, various symmetrical diaryl ketones were synthesized in moderate to good yield in the presence of a palladium catalyst.Setting the ke-tone: A convenient method for the palladium-catalyzed carbonylative homocoupling of aryl iodides is developed. By using formic acid as the CO source, various symmetrical diaryl ketones can be produced in moderate to good yields. DPEphos=bis[(2-diphenylphosphino)phenyl] ether, DCC=N,N′-dicyclohexylcarbodiimide.
      PubDate: 2017-11-21T03:33:38.738459-05:
      DOI: 10.1002/cctc.201701185
       
  • Mechanisms of Two-Electron versus Four-Electron Reduction of Dioxygen
           Catalyzed by Earth-Abundant Metal Complexes
    • Authors: Shunichi Fukuzumi; Yong-Min Lee, Wonwoo Nam
      Abstract: The two-electron reduction of dioxygen with two protons produces hydrogen peroxide, which is directly used as a liquid fuel in hydrogen peroxide fuel cells, whereas the four-electron reduction of dioxygen is combined with the two-electron oxidation of hydrogen in hydrogen fuel cells. Platinum (Pt)-based nanocomposites are the most efficient commercial electrocatalysts for the oxygen reduction reaction (ORR). However, the poor stability, scarcity and high cost of these Pt-based oxygen electrocatalysts are major barriers for the large-scale implementation of fuel cell technologies. Replacing noble metal-based electrocatalysts with highly efficient and inexpensive earth-abundant metal-based oxygen electrocatalysts has been of critical importance for practical applications. To develop efficient catalysts for the two-electron and four-electron reduction of dioxygen, it is crucially important to clarify the catalytic mechanisms of two-electron/two-proton versus four-electron/four-proton reduction of dioxygen with earth-abundant metal complexes. This review focused on the factors that control the two-electron/two-proton versus four-electron/four-proton reduction of dioxygen by electron donors (one electron reductants) such as ferrocene, catalyzed by earth-abundant metal complexes such as iron, cobalt, copper, manganese and nickel complexes in the homogeneous phase, by detecting catalytic intermediates, which determine the catalytic pathways of the two-electron versus four-electron reduction of dioxygen. The electrocatalytic two-electron or/and four-electron reduction of dioxygen with earth-abundant metal complexes and metal oxides has also been discussed in relation with the homogeneous catalysis.Two or four' The development of highly efficient inexpensive earth-abundant metal-based oxygen electrocatalysts that will replace noble metal-based ones requires an understanding of the catalytic mechanisms of the two-electron/two-proton and four-electron/four-proton reductions of dioxygen, which are important processes for fuel cell technologies and are typically catalyzed by costly Pt-based electrocatalysts. This Review is focused on the factors that control these reductions, catalyzed by earth-abundant metal complexes.
      PubDate: 2017-11-20T05:10:49.546383-05:
      DOI: 10.1002/cctc.201701064
       
  • Zeolitic Materials for DeNOx Selective Catalytic Reduction
    • Authors: Ying Xin; Qian Li, Zhaoliang Zhang
      Abstract: Selective catalytic reduction (SCR) of NOx has been proven to be the most efficient technique for the removal of NOx (deNOx) from flue gas of stationary sources and diesel engine exhaust of mobile sources. Among various SCR catalysts, zeolites are considered as the most promising candidates for heavy-duty trucks owing to their benign nature, very high NOx conversion and N2 selectivity, as well as excellent hydrothermal stability at high temperatures. In recent years, a tremendous number of research articles have reported on the evolution of zeolitic materials for deNOx, which makes a critical review timely to provide inspiration for future development. This paper first gives a chronological progress of zeolite catalysts specifically highlighting the CHA zeolites, the hotspot of present research and application, followed by a summary on the synthesis of CHA zeolites, the structure–activity relationships, as well as the reaction mechanisms and kinetics. Last but not least, a critical outlook is given together with expected research directions in developing zeolite-based catalysts for deNOx.This review gives a chronological progress of zeolite catalysts specifically highlighting CHA zeolites. The synthesis of CHA zeolites, the structure–activity relationships, as well as the reaction mechanisms and kinetics are summarized. A critical outlook is given together with expected research directions in developing zeolite-based catalysts for deNOx.
      PubDate: 2017-11-17T05:50:47.880111-05:
      DOI: 10.1002/cctc.201700854
       
  • Heteroatom-Doped Carbonaceous Photocatalysts for Solar Fuel Production and
           Environmental Remediation
    • Authors: Zhongkui Zhao; Guifang Ge, Di Zhang
      Abstract: Photocatalytic solar energy conversion and environmental remediation including water splitting, CO2 reduction, and pollutant degradation have attracted rapidly growing attention, owing to global fossil fuel depletion and increasing environmental issues. From the viewpoint of the broad availability, good environmental acceptability, high corrosion resistance, as well as the readily tailorable microstructure, electronic structure and surface chemical properties, carbonaceous materials have been demonstrated as promising and sustainable low-cost metal-free alternatives to metal-based photocatalysts for solar fuel production and pollutant degradation. The non-metallic heteroatoms doping approach has been considered as a powerful tool for modulating electronic structure, morphology, surface structure and surface chemistry, textural properties, optical properties, and electrochemical properties, as well as catalytic properties of carbonaceous photocatalysts. This Review represents a comprehensive overview of the latest advance in preparation and physicochemical properties of diverse non-metallic heteroatoms-doped carbonaceous materials, as well as their applications in heterogeneous photocatalysis towards solar energy conversion and environmental remediation. The physicochemical properties and photocatalytic performance of the carbonaceous photocatalysts are carefully compared, as well as a brief overview of fundamental principles for the promoting effect of heteroatoms-doping is also presented. In addition, the future perspectives on the opportunities and challenges of heteroatoms doping for fabricating novel and excellent carbonaceous photocatalysts are outlined.Heteroatom doping is a powerful tool for modulating electronic structure, geometrical structure, surface chemistry, and subsequent electronic conductivity, optical properties, and photocatalysis of carbon materials. This Review emphasizes the synthesis, properties, and photocatalytic applications of doped carbonaceous materials, discusses the fundamental understanding of promoting effect of doping, and also outlines the challenges and future perspectives.
      PubDate: 2017-11-16T09:11:24.904087-05:
      DOI: 10.1002/cctc.201700707
       
  • Trends of Alkane Activation on Doped Cobalt (II, III) Oxide from
           First Principles
    • Authors: Victor Fung; Franklin (Feng) Tao, De-en Jiang
      Abstract: The surface doping of a metal oxide can tune its catalytic performance, but it remains unclear how the tuning depends on the dopant type and the surface facet. Herein we study doped Co3O4 (1 1 1) and (3 1 1) surface facets using first-principles density functional theory (DFT) to obtain general descriptors for oxygen reactivity (which include vacancy formation energy and hydrogen adsorption energy) and correlate them to ethane C−H activation energy as a measure of the catalytic performance. The periodic trends of the dopants are investigated for a total of 20 dopants, namely, the elements from K to Ge. We find strong linear correlations between the oxygen reactivity descriptors and the computed energy barriers. We also discover a strong surface facet sensitivity among certain dopants such that different surface orientations and sites lead to different or even the opposite dopant performance. This work provides a useful guide for dopant performance in ethane activation on the two very different Co3O4 surfaces.Sensitive to doping: A systematic analysis of oxygen reactivity and a has been performed for ethane C−H activation on doped Co3O4 (1 1 1) and (3 1 1) surfaces. Trends and correlations are found that will provide a useful guide for dopant performance in ethane activation on the surfaces of transition metal oxides.
      PubDate: 2017-11-15T06:50:36.506659-05:
      DOI: 10.1002/cctc.201700960
       
  • Silver-Doped Cobalt (Magnesium) Aluminum Mixed Metal Oxides as Potential
           Catalysts for Nitrous Oxide Decomposition
    • Authors: Eng. Magdalena Jabłońska; Lorenzo Buselli, Eng. Marek Nocuń, Regina Palkovits
      Abstract: N2O is a potent greenhouse gas released among others in nitric and adipic acid production as well as from stationary and mobile combustion sources. A catalytic decomposition is highly attractive but requires catalysts active over a broad temperature range and in the presence of inhibiting compounds such as NO and O2. Ag-doped Co-(Mg)-Al-Ox mixed metal oxides obtained by the coprecipitation of metal nitrate precursors followed by calcination were evaluated as potential catalysts for N2O decomposition (deN2O) also in the presence of NO and/or O2. Ag integration during synthesis proved to be essential for superior catalytic activity. The catalyst with the optimum composition, AgCo3Al-Ox (Co/Al=3:1 mol %, 1.0 wt % Ag), achieved full N2O conversion at 350 and 450 °C under N2O/N2 and N2O/NO/O2/N2 conditions, respectively. Catalyst characterization, with a focus on H2 temperature-programmed reduction and X-ray photoelectron spectroscopy, evidenced that abundant Ag0 on the surface of (1.0–2.8 wt %)AgCo3Al-Ox enhanced the reduction of cobalt spinels to enable the superior catalytic performance.Catalytic N2O decomposition: We conduct catalytic N2O decomposition over Ag-doped Co3(Mg)Al-Ox mixed metal oxides. Co3Al-Ox doped with 1.0 wt % Ag showed full N2O conversion at 350 and 450 °C under N2O/N2 and N2O/NO/O2/N2 conditions, respectively. Abundant Ag0 on the surface of AgCo3Al-Ox enhances the reduction of cobalt spinels.
      PubDate: 2017-11-10T10:21:32.419268-05:
      DOI: 10.1002/cctc.201700777
       
  • Effect of Reduction Treatment on CO Oxidation with CeO2 Nanorod-Supported
           CuOx Catalysts
    • Authors: Samantha A. Mock; Elizabeth T. Zell, Shaikh T. Hossain, Ruigang Wang
      Abstract: Understanding the correlation of thermal treatment with catalyst activity provides mechanistic information about how the catalysts can be activated or deactivated. In this paper, we report that a comparative study was conducted on CeO2 nanorod-supported CuOx catalysts before and after reduction treatment to gain insight on the effects of the copper oxidation state and catalyst–support interfacial interactions on CO oxidation. X-ray diffraction, Raman spectroscopy, hydrogen temperature-programmed reduction (H2-TPR), and transmission electron microscopy (TEM) were used in a comprehensive way to study the effects of CuOx (0≤x≤1) composition as well as their spatial distribution on CeO2 nanorods on the H2 consumption and CO oxidation of the catalysts. These techniques were then used to gain a better understanding of the correlation between the different copper species (α, β, and γ-type CuOx) and the multiple reduction (H2 consumption) peaks, found in the H2-TPR data during the first run and during in situ reduction and redox cycling experiments. Also concluded from this study is that an abundance of surface defects are found on CeO2 nanorods from high-resolution TEM, which consequently may be critical to strong CuOx(0≤x≤1)–CeO2−x(0≤x≤0.5) interactions, therefore resulting in the improved low-temperature catalytic activity.Effect of reduction treatment: A comparative study was conducted on CeO2 nanorod-supported CuOx catalysts before and after reduction treatment to gain insight on the effects of the copper oxidation state and catalyst–support interfacial interactions on CO oxidation. An abundance of surface defects are found on CeO2 nanorods from high-resolution TEM, which consequently may be critical to strong CuOx(0≤x≤1)–CeO2−x(0≤x≤0.5) interactions, therefore resulting in the improved low-temperature catalytic activity.
      PubDate: 2017-11-09T12:25:54.908948-05:
      DOI: 10.1002/cctc.201700972
       
  • Diastereoselective Cyclization of 1,5-Dienes with the C−H Bond of
           Pyridine Catalyzed by a Cationic Mono(phosphinoamide) Alkyl Scandium
           Complex
    • Authors: Yanhui Chen; Di Song, Jing Li, Xiaoyan Hu, Xianjia Bi, Tao Jiang, Zhaomin Hou
      Abstract: The carbocyclization of non-conjugated dienes mediated by organometallics is an important reaction for the synthesis of a variety of carbocyclic derivatives, but the direct annulation of dienes with an inert C−H bond of a substrate has remained unexplored to date. We herein report a series of novel rare-earth dialkyl complexes bearing a phosphinoamide anion and demonstrate that the combination of a mono(phosphinoamido)-ligated scandium dialkyl complex with B(C6F5)3 results in an excellent catalyst for the cis-selective cyclization of 1,5-dienes with the ortho-C(sp2)−H bond of pyridines to afford a new family of pyridyl-functionalized 1,3-disubstituted cyclopentane derivatives containing monocyclic, bicyclic, spirocyclic, and heterocyclic skeletons in moderate to excellent yields with high diastereoselectivities (cis/trans up to 99:1).It rings true: The combination of a novel mono(phosphinoamido)-ligated scandium complex such as 2 a-Sc with a boron compound such as B(C6F5)3 results in a unique and highly efficient catalyst for the cis-selective cyclization of 1,5-dienes with the ortho-C(sp2)−H bond of pyridines. The resulting pyridyl-functionalized 1,3-disubstituted cyclopentane derivatives are obtained in excellent yields with high diastereoselectivities.
      PubDate: 2017-11-08T09:09:09.880724-05:
      DOI: 10.1002/cctc.201700980
       
  • Confining Gold Nanoclusters in Highly Defective Graphitic Layers To
           Enhance the Methanol Electrooxidation Reaction
    • Authors: Zhe Mao; Haihua Hu, Rui Su, Peizhi Liu, Yixing Li, Wenting Zhang, Xiaoning Zhao, Junjie Guo, Pengfei Guan, Gaowu Qin, Xuefeng Zhang
      Abstract: The development of a highly efficient catalyst possessing both high activity and remarkable stability is a major focus in fuel-cell applications. Herein, we utilized an arc-discharge approach with an ultrafast cooling system to synthesize a core@shell structural Au@C nanocomposite comprising 3–5 nm gold clusters confined within highly defective graphitic layers. Such a construction not only improves the conductivity to accelerate the penetration of ions and electrons during the electrocatalytic process of methanol molecules, but it also suppresses chemical/thermal coarsening of the gold clusters. More importantly, the atomic-scale Au/C interfaces contribute to a synergistic effect and enhance the activity relative to that of other gold-based catalysts in the electrooxidation of methanol. This work highlights the role of heterogeneous interfaces in the catalytic efficiency of precious-metal catalysts and rationalizes optimization in catalyst engineering.Good as gold: A Au@C nanocomposite comprising 3–5 nm gold clusters confined within few-layered, highly defective graphitic cages is prepared; this nanocomposite exhibits high catalytic activity and excellent stability for the electrooxidation of methanol. The defective graphitic layers prohibit chemical/thermal coarsening of the gold clusters and also provide effective penetration channels for the transport of ions/electrons during the catalytic reaction.
      PubDate: 2017-11-08T09:08:43.771565-05:
      DOI: 10.1002/cctc.201700895
       
  • Zwitterionic imidazole-urea derivative framework bridged mesoporous hybrid
           silica: highly efficient heterogeneous nanocatalyst for CO2 conversion
    • Authors: Jianmin Sun; Mengshuai Liu, Xingyuan Lu, Yichen Jiang, Masahiko Arai
      Abstract: The use of supported zwitterionic nanoparticles is an interesting and important strategy for developing new CO2 conversion catalysts with enhanced activity and selectivity. Several zwitterionic imidazole-urea derivative frameworks bridged mesoporous hybrid silica materials were prepared and characterized by FTIR, MAS solid-state NMR, XPS, XRD, TEM and TGA techniques. The novel Im-Si-X-φ materials prepared possess multi-functionalities of high surface area, hydrogen bond donor (HBD) ability, and nucleophilicity. A material that contains iodine and is protonated by an inorganic acid shows excellent catalytic activity for CO2 conversion into cyclic carbonates with good recyclability. Reaction parameters on cycloaddition of CO2 with propylene oxide (PO) to propylene carbonate (PC) were optimized. The one-component material is an efficient heterogeneous catalyst for CO2 cycloaddition reactions, which is much greener alternative to conventional supported transition metal catalysts. Its catalytic features were also compared to unsupported counterpart of free ionic compound and other supported catalysts reported in the literature.
      PubDate: 2017-10-24T09:57:53.4561-05:00
      DOI: 10.1002/cctc.201701492
       
  • Biocatalytic Potential of Enzymes Involved in the Biosynthesis of
           Isoprenoid Quinones
    • Authors: Godwin A. Aleku; Beatrycze Nowicka, Nicholas J. Turner
      Pages: 124 - 135
      Abstract: Naturally occurring isoprenoid quinones mediate electron transfer in respiratory or photosynthetic chains of living organisms. Tremendous progress has been made in the elucidation of biosynthetic pathways of prenylated quinones and a number of enzymes that catalyze specific transformation steps with remarkably high regio- and stereoselectivity have been characterized. Interestingly, some of these enzymes possess broad substrate scope towards synthetic analogues, thereby enabling their application as synthetic tools. The availability of mechanistic, structural and mutagenesis information for many of the pathway enzymes presents opportunities for protein engineering, a powerful approach that may improve the suitability of these biocatalysts for industrial processes.This Minireview discusses the biocatalytic applicability of key enzymes for the biosynthesis of isoprenoid quinones. Proof of concept of synthetic applications of these biocatalysts and efforts made to engineer them are highlighted.
      PubDate: 2017-10-02T08:56:11.620903-05:
      DOI: 10.1002/cctc.201700685
       
  • N-Hydroxyphthalimide Anchored on Diamond Nanoparticles as a Selective
           Heterogeneous Metal-free Oxidation Catalyst of Benzylic Hydrocarbons and
           Cyclic Alkenes by Molecular O2
    • Authors: Juan F. Blandez; Sergio Navalón, Mercedes Álvaro, Hermenegildo García
      Pages: 198 - 205
      Abstract: N-hydroxyphthalimide (NHPI) derived from trimellitic anhydride has been covalently anchored (4 wt %) through ester bonds to the surface of commercial diamond nanoparticles previously functionalized by chemical and thermal treatments (DH). IR spectroscopy of the NHPI/DH solid shows the presence of a characteristic peak at 1735 cm−1 attributable to the ester bond, while solid-state MAS 13C NMR spectroscopy shows two broad bands corresponding to carbon atoms of carbonyl groups (167 ppm) and aromatic carbons (127 ppm). NHPI/DH promotes autoxidation of isobutylbenzene involving superoxide (O2.−) and hydroperoxide (HOO⋅) radicals; NHPI/DH can be reused at least three times and reach a minimum turnover number as high as 20 600, which is probably due to the inertness of the diamond surface, allowing free diffusion of reactive oxygen species. Analogous materials in which NHPI was anchored on activated carbon and multiwall carbon nanotubes were inefficient as autoxidation catalysts. NHPI/DH is able to promote also selective aerobic oxidation of other benzylic hydrocarbons and cycloalkenes.Diamond cats: In contrast to analogous active carbons and multiwall carbon nanotubes, OH functionalized diamond nanoparticles are suitable supports to develop heterogeneous oxidation catalysts based on anchored N-hydroxyphthalimide.
      PubDate: 2017-09-07T04:46:03.213948-05:
      DOI: 10.1002/cctc.201700886
       
  • Facile Synthesis of a Novel Hierarchical ZSM-5 Zeolite: A Stable Acid
           Catalyst for Dehydrating Glycerol to Acrolein
    • Authors: Rolf Beerthuis; Liang Huang, N. Raveendran Shiju, Gadi Rothenberg, Wei Shen, Hualong Xu
      Pages: 211 - 221
      Abstract: Catalytic biomass conversion is often hindered by coking. Carbon compounds cover active surface and plug pores, causing catalyst deactivation. Material design at the nanoscale allows tailoring of the catalytic activity and stability. Here, we report a simple synthesis of nanosized ZSM-5 materials by using a silicalite-1 seeding suspension. ZSM-5 crystals were grown from a deionized silica source in the presence of ammonia. By using silicalite-1 seeds, crystalline ZSM-5 is synthesized without any structure-directing agent. This method allows parallel preparation of a range of ZSM-5 samples, eliminating time-consuming ion-exchange steps. Mesoporosity is introduced by formation of intercrystallite voids, owing to nanocrystal agglomeration. The effects of crystal sizes and morphologies are then evaluated in the catalytic dehydration of glycerol to acrolein, with results compared against commercial ZSM-5. The most active nanosized ZSM-5 catalysts were five times more stable compared with commercial ZSM-5, giving quantitative conversion and twice the acrolein yield compared with the commercial catalyst. The influence of the catalyst structure on the chemical diffusion and the resistance to coking are discussed.Hierarchical zeolite seeding: The synthesis of nanosized ZSM-5 materials by using a silicalite-1 seeding suspension is reported. This method allows parallel preparation of a range of ZSM-5 samples, eliminating time-consuming ion-exchange steps and the need for a structure-directing agent. The effects of crystal sizes and morphologies are evaluated in the catalytic dehydration of glycerol to acrolein.
      PubDate: 2017-10-16T08:26:04.798472-05:
      DOI: 10.1002/cctc.201700663
       
  • Improving Carbon-Coated TiO2 Films with a TiCl4 Treatment for
           Photocatalytic Water Purification
    • Authors: Gylen Odling; Aruna Ivaturi, Efthalia Chatzisymeon, Neil Robertson
      Pages: 234 - 243
      Abstract: By using a simple thermal decomposition route, carbon-TiO2 hybrid films have been synthesized from a catechol-TiO2 surface complex. The coated films display enhanced visible region absorption, owing to the thin (≈2 nm) layer of carbon encapsulating the TiO2. Although photocatalytically active under visible light alone, it is demonstrated that the activity of the carbon-coated films can be improved further by a hydrolytic treatment with TiCl4, leading to the introduction of small TiO2 particles (5–10 nm) and doping of chlorine into the structure. The combination of the carbon layer and TiCl4 treatment gives increased photocatalytic performance for the photodegradation of dyes, phenolic pollutants and the reduction of toxic CrVI to relatively benign CrIII. In addition, the carbon-coated films show improved bactericidal activity under UV irradiation, and hence have been successfully tested against the most common types of pollutant present in potential drinking waters.Water purification catalyst: Carbon-TiO2 hybrid films have been synthesized from a catechol-TiO2 surface complex. The coated films display enhanced visible region absorption. The activity can be improved further by a hydrolytic treatment with TiCl4, leading to the introduction of small TiO2 particles (5–10 nm) and doping of chlorine into the structure. The films were used to remove organic, inorganic and bacterial pollutants from water.
      PubDate: 2017-09-21T07:56:14.865229-05:
      DOI: 10.1002/cctc.201700867
       
  • Mesoporous Ni(OH)2/CeNixOy Composites Derived Ni/CeNixOy Catalysts for Dry
           Reforming of Methane
    • Authors: Jian Dou; Zhenghong Bao, Fei Yu
      Pages: 250 - 258
      Abstract: Designing stable nickel-based catalysts is critical for dry reforming of methane with carbon dioxide (DRM) to produce fuels and chemicals. Herein, mesoporous Ni(OH)2/CeNixOy composites were prepared by a one-pot hydrothermal synthetic route. Aggregation of Ni(OH)2 nanoplates and CeNixOy nanocrystals generates mesopores from the void space and creates a surface area as high as 138 m2 g−1. With the Ni content in the range of 0.7–12.5 %, the mesoporous structure is stable after reduction with the highest surface area as 94 m2 g−1. Reduction of Ni(OH)2/CeNixOy composites at 500 °C converts Ni(OH)2 nanoplates into Ni nanoparticles. The size of the reduced Ni nanoparticles was controlled from 10 to 140 nm by adjusting the Ni loading from 0.7 to 42.7 %. The catalysts with Ni/(Ni+Ce) ratios of 0.4 and 0.5, 0.4 Ni/CeNixOy and 0.5 Ni/CeNixOy, respectively, exhibit enhanced catalytic performance for DRM reaction with their activities 3–5 times as high as those of 0.6 Ni/CeNixOy and 0.8 Ni/CeNixOy catalysts, owing to the good dispersion of 10 nm Ni nanoparticles within mesoporous CeNixOy. Furthermore, the 0.5 Ni/CeNixOy catalyst is very stable for DRM for 140 h. The robust stability of 0.5 Ni/CeNixOy catalyst possibly stems from the strong interactions between Ni nanoparticles and the CeNixOy surface, which stabilize Ni nanoparticles during DRM reaction.Voids to pores: A mesoporous Ni/CeNixOy catalyst synthesized by the hydrothermal method exhibits good dispersion of 10 nm Ni nanoparticles within the mesoporous CeNixOy structure, promoting a stable production of syngas in the dry reforming of methane with carbon dioxide.
      PubDate: 2017-11-08T04:56:49.545157-05:
      DOI: 10.1002/cctc.201701073
       
  • Rhodium Pyrrolylphosphine Complexes as Highly Active and Selective
           Catalysts for Propene Hydroformylation: The Effect of Water and Aldehyde
           on the Reaction Regioselectivity
    • Authors: Ewa Mieczyńska; Ryzard Grzybek, Anna M. Trzeciak
      Pages: 305 - 310
      Abstract: The hydroformylation of propene catalyzed by Rh(acac)(CO)2 (acac=acetylacetonate) with a 13-fold excess of N-pyrrolylphosphine ligands PPyr3, PPh2Pyr, or PPh(Pyr)2 (Pyr=NC4H4) was investigated under a pressure of 15 bar (propene/H2/CO=5:5:5) at 80 °C. The N-pyrrolylphosphine ligands facilitated an excellent regioselectivity towards n-butanal aldehyde, significantly better than PPh3 and PCy3 under the same conditions. In the presence of the strongest π-acceptor, PPyr3, the linear-to-branched aldehyde (l/b) ratio was 8.6, which increased to 27.1 if water was added to the system. The application of a pure aldehyde as a solvent instead of toluene caused a significant increase in the aldehyde yield but with a decreased l/b ratio (2.9–7.6). The regioselectivity parameter l/b increased to 19.3 after the introduction of water as a cosolvent.Pyrrolylphosphines prosper: The hydroformylation of propene catalyzed by Rh(acac)(CO)2 (acac=acetylacetonate) with a 13-fold excess of N-pyrrolylphosphine ligands PPyr3, PPh2Pyr, or PPh(Pyr)2 (Pyr=NC4H4) is investigated under a pressure of 15 bar (propene/H2/CO=5:5:5) at 80 °C. The N-pyrrolylphosphine ligands facilitate an excellent regioselectivity towards n-butanal aldehyde, significantly better than PPh3 and PCy3 under the same conditions.
      PubDate: 2017-11-08T09:08:32.928497-05:
      DOI: 10.1002/cctc.201700917
       
  • Rapid Synthesis of Rhodium–Palladium Alloy Nanocatalysts
    • Authors: Graham W. Piburn; Hao Li, Pranaw Kunal, Graeme Henkelman, Simon M. Humphrey
      Pages: 329 - 333
      Abstract: The chemistry of metastable RhPd alloys is not well understood, and well-characterized nanoparticle (NP) examples remain rare. Well-defined and near-monodisperse RhPd NPs were prepared in a simple one-pot approach by using microwave-assisted or conventional heating in reaction times as short as 30 s. The catalytic hydrogenation activity of supported RhPd NP catalysts revealed that short synthesis times resulted in the most-active and most-stable hydrogenation catalysts, whereas longer synthesis times promoted partial Rh-Pd core–shell segregation. Relative to Rh NPs, RhPd NPs resisted deactivation over longer reaction times. Density functional theory (DFT) was employed to estimate the binding energies of H and alkenes on (1 1 1) Rh, Pd, and Rh0.5Pd0.5 surfaces. The DFT results concurred with experiment and concluded that the alkene hydrogenation activity trend was of the order Pd
      PubDate: 2017-09-14T04:42:07.932626-05:
      DOI: 10.1002/cctc.201701133
       
 
 
JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
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