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  Subjects -> MATHEMATICS (Total: 874 journals)
    - APPLIED MATHEMATICS (71 journals)
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    - MATHEMATICS (647 journals)
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MATHEMATICS (647 journals)                  1 2 3 4 | Last

Showing 1 - 200 of 538 Journals sorted alphabetically
Abakós     Open Access   (Followers: 3)
Abhandlungen aus dem Mathematischen Seminar der Universitat Hamburg     Hybrid Journal   (Followers: 2)
Academic Voices : A Multidisciplinary Journal     Open Access   (Followers: 2)
Accounting Perspectives     Full-text available via subscription   (Followers: 7)
ACM Transactions on Algorithms (TALG)     Hybrid Journal   (Followers: 16)
ACM Transactions on Computational Logic (TOCL)     Hybrid Journal   (Followers: 4)
ACM Transactions on Mathematical Software (TOMS)     Hybrid Journal   (Followers: 6)
ACS Applied Materials & Interfaces     Full-text available via subscription   (Followers: 21)
Acta Applicandae Mathematicae     Hybrid Journal   (Followers: 1)
Acta Mathematica     Hybrid Journal   (Followers: 11)
Acta Mathematica Hungarica     Hybrid Journal   (Followers: 2)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5)
Acta Mathematica Sinica, English Series     Hybrid Journal   (Followers: 5)
Acta Mathematica Vietnamica     Hybrid Journal  
Acta Mathematicae Applicatae Sinica, English Series     Hybrid Journal  
Advanced Science Letters     Full-text available via subscription   (Followers: 5)
Advances in Applied Clifford Algebras     Hybrid Journal   (Followers: 3)
Advances in Calculus of Variations     Hybrid Journal   (Followers: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5)
Advances in Complex Systems     Hybrid Journal   (Followers: 7)
Advances in Computational Mathematics     Hybrid Journal   (Followers: 15)
Advances in Decision Sciences     Open Access   (Followers: 4)
Advances in Difference Equations     Open Access   (Followers: 1)
Advances in Fixed Point Theory     Open Access   (Followers: 5)
Advances in Geosciences (ADGEO)     Open Access   (Followers: 10)
Advances in Linear Algebra & Matrix Theory     Open Access   (Followers: 1)
Advances in Materials Sciences     Open Access   (Followers: 16)
Advances in Mathematical Physics     Open Access   (Followers: 6)
Advances in Mathematics     Full-text available via subscription   (Followers: 10)
Advances in Numerical Analysis     Open Access   (Followers: 4)
Advances in Operations Research     Open Access   (Followers: 11)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Pure and Applied Mathematics     Hybrid Journal   (Followers: 5)
Advances in Pure Mathematics     Open Access   (Followers: 4)
Advances in Science and Research (ASR)     Open Access   (Followers: 6)
Aequationes Mathematicae     Hybrid Journal   (Followers: 2)
African Journal of Educational Studies in Mathematics and Sciences     Full-text available via subscription   (Followers: 5)
African Journal of Mathematics and Computer Science Research     Open Access   (Followers: 4)
Afrika Matematika     Hybrid Journal   (Followers: 1)
Air, Soil & Water Research     Open Access   (Followers: 7)
AKSIOMA Journal of Mathematics Education     Open Access   (Followers: 1)
Algebra and Logic     Hybrid Journal   (Followers: 3)
Algebra Colloquium     Hybrid Journal   (Followers: 4)
Algebra Universalis     Hybrid Journal   (Followers: 2)
Algorithmic Operations Research     Full-text available via subscription   (Followers: 5)
Algorithms     Open Access   (Followers: 9)
Algorithms Research     Open Access   (Followers: 1)
American Journal of Biostatistics     Open Access   (Followers: 9)
American Journal of Computational and Applied Mathematics     Open Access   (Followers: 3)
American Journal of Mathematical Analysis     Open Access  
American Journal of Mathematics     Full-text available via subscription   (Followers: 7)
American Journal of Operations Research     Open Access   (Followers: 5)
American Mathematical Monthly     Full-text available via subscription   (Followers: 6)
An International Journal of Optimization and Control: Theories & Applications     Open Access   (Followers: 7)
Analele Universitatii Ovidius Constanta - Seria Matematica     Open Access   (Followers: 1)
Analysis     Hybrid Journal   (Followers: 2)
Analysis and Applications     Hybrid Journal   (Followers: 1)
Analysis and Mathematical Physics     Hybrid Journal   (Followers: 4)
Analysis Mathematica     Full-text available via subscription  
Annales Mathematicae Silesianae     Open Access  
Annales mathématiques du Québec     Hybrid Journal   (Followers: 4)
Annales UMCS, Mathematica     Open Access   (Followers: 1)
Annales Universitatis Paedagogicae Cracoviensis. Studia Mathematica     Open Access  
Annali di Matematica Pura ed Applicata     Hybrid Journal   (Followers: 1)
Annals of Combinatorics     Hybrid Journal   (Followers: 3)
Annals of Data Science     Hybrid Journal   (Followers: 8)
Annals of Discrete Mathematics     Full-text available via subscription   (Followers: 6)
Annals of Mathematics     Full-text available via subscription  
Annals of Mathematics and Artificial Intelligence     Hybrid Journal   (Followers: 6)
Annals of Pure and Applied Logic     Open Access   (Followers: 2)
Annals of the Alexandru Ioan Cuza University - Mathematics     Open Access  
Annals of the Institute of Statistical Mathematics     Hybrid Journal   (Followers: 1)
Annals of West University of Timisoara - Mathematics     Open Access  
Annuaire du Collège de France     Open Access   (Followers: 5)
Applicable Algebra in Engineering, Communication and Computing     Hybrid Journal   (Followers: 2)
Applications of Mathematics     Hybrid Journal   (Followers: 1)
Applied Categorical Structures     Hybrid Journal   (Followers: 2)
Applied Computational Intelligence and Soft Computing     Open Access   (Followers: 12)
Applied Mathematics     Open Access   (Followers: 3)
Applied Mathematics     Open Access   (Followers: 4)
Applied Mathematics & Optimization     Hybrid Journal   (Followers: 4)
Applied Mathematics - A Journal of Chinese Universities     Hybrid Journal  
Applied Mathematics Letters     Full-text available via subscription   (Followers: 1)
Applied Mathematics Research eXpress     Hybrid Journal   (Followers: 1)
Applied Network Science     Open Access  
Applied Numerical Mathematics     Hybrid Journal   (Followers: 5)
Applied Spatial Analysis and Policy     Hybrid Journal   (Followers: 4)
Arab Journal of Mathematical Sciences     Open Access   (Followers: 2)
Arabian Journal of Mathematics     Open Access   (Followers: 2)
Archive for Mathematical Logic     Hybrid Journal   (Followers: 1)
Archive of Applied Mechanics     Hybrid Journal   (Followers: 4)
Archive of Numerical Software     Open Access  
Archives of Computational Methods in Engineering     Hybrid Journal   (Followers: 4)
Arkiv för Matematik     Hybrid Journal   (Followers: 1)
Arnold Mathematical Journal     Hybrid Journal   (Followers: 1)
Artificial Satellites : The Journal of Space Research Centre of Polish Academy of Sciences     Open Access   (Followers: 18)
Asia-Pacific Journal of Operational Research     Hybrid Journal   (Followers: 3)
Asian Journal of Algebra     Open Access   (Followers: 1)
Asian Journal of Current Engineering & Maths     Open Access  
Asian-European Journal of Mathematics     Hybrid Journal   (Followers: 2)
Australian Mathematics Teacher, The     Full-text available via subscription   (Followers: 7)
Australian Primary Mathematics Classroom     Full-text available via subscription   (Followers: 2)
Australian Senior Mathematics Journal     Full-text available via subscription   (Followers: 1)
Automatic Documentation and Mathematical Linguistics     Hybrid Journal   (Followers: 5)
Axioms     Open Access  
Baltic International Yearbook of Cognition, Logic and Communication     Open Access  
Basin Research     Hybrid Journal   (Followers: 3)
BIBECHANA     Open Access  
BIT Numerical Mathematics     Hybrid Journal  
BoEM - Boletim online de Educação Matemática     Open Access  
Boletim Cearense de Educação e História da Matemática     Open Access  
Boletim de Educação Matemática     Open Access  
Boletín de la Sociedad Matemática Mexicana     Hybrid Journal  
Bollettino dell'Unione Matematica Italiana     Full-text available via subscription   (Followers: 1)
British Journal of Mathematical and Statistical Psychology     Full-text available via subscription   (Followers: 21)
Bruno Pini Mathematical Analysis Seminar     Open Access  
Buletinul Academiei de Stiinte a Republicii Moldova. Matematica     Open Access   (Followers: 7)
Bulletin des Sciences Mathamatiques     Full-text available via subscription   (Followers: 4)
Bulletin of Dnipropetrovsk University. Series : Communications in Mathematical Modeling and Differential Equations Theory     Open Access   (Followers: 1)
Bulletin of Mathematical Sciences     Open Access   (Followers: 1)
Bulletin of the Brazilian Mathematical Society, New Series     Hybrid Journal  
Bulletin of the London Mathematical Society     Hybrid Journal   (Followers: 3)
Bulletin of the Malaysian Mathematical Sciences Society     Hybrid Journal  
Calculus of Variations and Partial Differential Equations     Hybrid Journal  
Canadian Journal of Science, Mathematics and Technology Education     Hybrid Journal   (Followers: 17)
Carpathian Mathematical Publications     Open Access   (Followers: 1)
Catalysis in Industry     Hybrid Journal   (Followers: 1)
CEAS Space Journal     Hybrid Journal  
CHANCE     Hybrid Journal   (Followers: 5)
Chaos, Solitons & Fractals     Hybrid Journal   (Followers: 3)
ChemSusChem     Hybrid Journal   (Followers: 7)
Chinese Annals of Mathematics, Series B     Hybrid Journal  
Chinese Journal of Catalysis     Full-text available via subscription   (Followers: 2)
Chinese Journal of Mathematics     Open Access  
Clean Air Journal     Full-text available via subscription   (Followers: 2)
Cogent Mathematics     Open Access   (Followers: 2)
Cognitive Computation     Hybrid Journal   (Followers: 4)
Collectanea Mathematica     Hybrid Journal  
College Mathematics Journal     Full-text available via subscription   (Followers: 2)
COMBINATORICA     Hybrid Journal  
Combustion Theory and Modelling     Hybrid Journal   (Followers: 13)
Commentarii Mathematici Helvetici     Hybrid Journal   (Followers: 1)
Communications in Contemporary Mathematics     Hybrid Journal  
Communications in Mathematical Physics     Hybrid Journal   (Followers: 1)
Communications On Pure & Applied Mathematics     Hybrid Journal   (Followers: 3)
Complex Analysis and its Synergies     Open Access   (Followers: 2)
Complex Variables and Elliptic Equations: An International Journal     Hybrid Journal  
Complexus     Full-text available via subscription  
Composite Materials Series     Full-text available via subscription   (Followers: 9)
Comptes Rendus Mathematique     Full-text available via subscription   (Followers: 1)
Computational and Applied Mathematics     Hybrid Journal   (Followers: 2)
Computational and Mathematical Methods in Medicine     Open Access   (Followers: 2)
Computational and Mathematical Organization Theory     Hybrid Journal   (Followers: 2)
Computational Complexity     Hybrid Journal   (Followers: 4)
Computational Mathematics and Modeling     Hybrid Journal   (Followers: 8)
Computational Mechanics     Hybrid Journal   (Followers: 4)
Computational Methods and Function Theory     Hybrid Journal  
Computational Optimization and Applications     Hybrid Journal   (Followers: 7)
Computers & Mathematics with Applications     Full-text available via subscription   (Followers: 5)
Concrete Operators     Open Access   (Followers: 4)
Confluentes Mathematici     Hybrid Journal  
COSMOS     Hybrid Journal  
Cryptography and Communications     Hybrid Journal   (Followers: 14)
Cuadernos de Investigación y Formación en Educación Matemática     Open Access  
Cubo. A Mathematical Journal     Open Access  
Czechoslovak Mathematical Journal     Hybrid Journal   (Followers: 1)
Demographic Research     Open Access   (Followers: 12)
Demonstratio Mathematica     Open Access  
Dependence Modeling     Open Access  
Design Journal : An International Journal for All Aspects of Design     Hybrid Journal   (Followers: 29)
Developments in Clay Science     Full-text available via subscription   (Followers: 1)
Developments in Mineral Processing     Full-text available via subscription   (Followers: 3)
Dhaka University Journal of Science     Open Access  
Differential Equations and Dynamical Systems     Hybrid Journal   (Followers: 2)
Discrete Mathematics     Hybrid Journal   (Followers: 7)
Discrete Mathematics & Theoretical Computer Science     Open Access  
Discrete Mathematics, Algorithms and Applications     Hybrid Journal   (Followers: 2)
Discussiones Mathematicae Graph Theory     Open Access   (Followers: 1)
Doklady Mathematics     Hybrid Journal  
Duke Mathematical Journal     Full-text available via subscription   (Followers: 1)
Edited Series on Advances in Nonlinear Science and Complexity     Full-text available via subscription  
Electronic Journal of Graph Theory and Applications     Open Access   (Followers: 2)
Electronic Notes in Discrete Mathematics     Full-text available via subscription   (Followers: 2)
Elemente der Mathematik     Full-text available via subscription   (Followers: 3)
Energy for Sustainable Development     Hybrid Journal   (Followers: 9)
Enseñanza de las Ciencias : Revista de Investigación y Experiencias Didácticas     Open Access  
Ensino da Matemática em Debate     Open Access  
Entropy     Open Access   (Followers: 5)
ESAIM: Control Optimisation and Calculus of Variations     Full-text available via subscription   (Followers: 1)
European Journal of Combinatorics     Full-text available via subscription   (Followers: 4)
European Journal of Mathematics     Hybrid Journal   (Followers: 1)
European Scientific Journal     Open Access   (Followers: 2)
Experimental Mathematics     Hybrid Journal   (Followers: 3)
Expositiones Mathematicae     Hybrid Journal   (Followers: 2)
Facta Universitatis, Series : Mathematics and Informatics     Open Access  
Fasciculi Mathematici     Open Access  
Finite Fields and Their Applications     Full-text available via subscription   (Followers: 4)
Fixed Point Theory and Applications     Open Access   (Followers: 1)
Formalized Mathematics     Open Access   (Followers: 2)
Foundations and Trends® in Econometrics     Full-text available via subscription   (Followers: 4)

        1 2 3 4 | Last

Journal Cover Chinese Journal of Catalysis
  [SJR: 0.6]   [H-I: 29]   [2 followers]  Follow
    
   Full-text available via subscription Subscription journal
   ISSN (Print) 1872-2067
   Published by Elsevier Homepage  [3042 journals]
  • Preface to Special Issue on Nanoscience and Catalysis
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Zhiyong Tang, Huijun Zhao
      Graphical abstract image

      PubDate: 2017-06-21T11:54:35Z
       
  • Recent advances in the rational design of electrocatalysts towards the
           oxygen reduction reaction
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Jianfei Kong, Wenlong Cheng
      The quest for low-cost yet efficient non-Pt electrocatalysts for the oxygen reduction reaction (ORR) has become one of the main focuses of research in the field of catalysis, which has implications for the development of the next generation of greener fuel cells. Here, we comprehensively describe the ‘big picture’ of recent advances made in the rational design of ORR electrocatalysts, including molecule-based, metal-oxide-based, metal-nanomaterial-based and two-dimensional electrocatalysts. Transition metals can fabricate molecular electrocatalysts with N4-macrocycles such as porphyrin-class compounds and the so-formed M–N–C active centre plays a crucial role in determining the catalytic performances towards the ORR. Group-IV and -V Transition metal oxides represent another class of promising alternative of Pt-based catalysts for the ORR which catalytic activity largely depends on the surface structure and the introduction of surface defects. Recent advances in synthesis of metallic nanoparticles (NPs) allow for precise control over particle sizes and shapes and the crystalline facets exposed to enhance the ORR performance of electrocatalysts. Two-dimensional materials such as functionalized grapheme or MoS2 are emerging as novel electrocatalysts for the ORR. This review covers various aspects towards the design of future ORR electrocatalysts, including the catalytic performance, stability, durability and cost. Some novel electrocatalysts even surpass commercial Pt/C systems, demonstrating their potential to be alternatives in industrial applications. Despite the encouraging progress, challenges, which are also described, remain to be overcome before the real-world application of novel ORR electrocatalysts.
      Graphical abstract image

      PubDate: 2017-06-21T11:54:35Z
       
  • Advanced yolk-shell nanoparticles as nanoreactors for energy conversion
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Meiwen Wang, Yash Boyjoo, Jian Pan, Shaobin Wang, Jian Liu
      Yolk-shell structured nanoparticles are of immense scientific and technological interests because of their unique architecture and myriad of applications. This review summarizes recent progresses in the use of yolk-shell structured nanoparticles as nanoreactors for various chemical reactions. A very brief overview of synthetic strategies is provided with emphasis on recent research progress in the last five years. Catalytic applications of these yolk-shell structured nanoreactors are then discussed by covering photocatalysis, methane reforming and electrochemical conversion. The state of the art research and perspective in future development are also highlighted.
      Graphical abstract image

      PubDate: 2017-06-21T11:54:35Z
       
  • Earth-abundant amorphous catalysts for electrolysis of water
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Wence Xu, Hongxia Wang
      The generation of hydrogen through the electrolysis of water has attracted attention as a promising way to produce and store energy using renewable energy sources. In this process, a catalyst is very important to achieve a high-energy conversion efficiency for the electrolysis of water. A good catalyst for water electrolysis should exhibit high catalytic activity, good stability, low cost and good scalability. Much research has been devoted to developing efficient catalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Traditionally, it has been accepted that a material with high crystallinity is important to serve as a good catalyst for HER and/or OER. Recently, catalysts for HER and/or OER in the electrolysis of water splitting based on amorphous materials have received much interest in the scientific community owing to the abundant unsaturated active sites on the amorphous surface, which form catalytic centers for the reaction of the electrolysis of water. We summarize the recent advances of amorphous catalysts for HER, OER and overall water splitting by electrolysis and the related fundamental chemical reactions involved in the electrolysis of water. The current challenges confronting the electrolysis of water and the development of more efficient amorphous catalysts are also discussed.
      Graphical abstract image

      PubDate: 2017-06-21T11:54:35Z
       
  • Cu nanoparticles supported on graphitic carbon nitride as an efficient
           electrocatalyst for oxygen reduction reaction
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Henan Li, Yanan Xu, Hansinee Sitinamaluwa, Kimal Wasalathilake, Dilini Galpaya, Cheng Yan
      High active and cost-effective electrocatalysts for the oxygen reduction reaction (ORR) are essential components of renewable energy technologies, such as fuel cells and metal/air batteries. Herein, we propose that ORR active Cu/graphitic carbon nitride (Cu/g-CN) electrocatalyst can be prepared via a facile hydrothermal reaction in the present of the ionic liquid (IL) bis(1-hexadecyl-3-methylimidazolium) tetrachlorocuprate [(C16mim)2CuCl4] and protonated g-CN. The as-prepared Cu/g-CN showed an impressive ORR catalytic activity that a 99 mV positive shift of the onset potential and 2 times kinetic current density can be clearly observed, comparing with the pure g-CN. In addition, the Cu/g-CN revealed better stability and methanol tolerance than commercial Pt/C (HiSPECTM 3000, 20%). Therefore, the proposed Cu/g-CN, as the inexpensive and efficient ORR electrocatalyst, would be a potential candidate for application in fuel cells.
      Graphical abstract image Highlights Cu supported on graphitic carbon nitride electrocatalyst was synthesized by a facile hydrothermal reaction and shows high catalytic activity for the oxygen reduction reaction in an alkaline electrolyte.

      PubDate: 2017-06-21T11:54:35Z
       
  • Platinum stabilized by defective activated carbon with excellent oxygen
           reduction performance in alkaline media
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Xuecheng Yan, Yi Jia, Longzhou Zhang, Xiangdong Yao
      The exploration of highly active and durable cathodic oxygen reduction reaction (ORR) catalysts with economical production cost is still the bottleneck to realize the large-scale commercialization of fuel cells and metal-air batteries. Given that carbon support is crucial to the electrocatalysts, and Pt is the best-known ORR catalyst so far, in this work, we employed a simple impregnation method for synthesizing a kind of defective activated carbon (D-AC) supported low Pt content electrocatalysts for the ORR. The reduction conditions of the Pt-containing precursor were firstly optimized, and the influence of the Pt loading amount on the ORR was investigated as well. The results show that the obtained D-AC@5.0%Pt sample (contains 5 wt% Pt) has surpassed the commercial Pt/C with 20 wt% Pt for the ORR in an alkaline solution. In the meantime, it is more stable than the commercial Pt/C. The outstanding ORR performance of the D-AC@5.0%Pt confirms that both the unique defects in the D-AC and the introduced Pt particles are indispensable to the ORR. Particularly, the ORR activity of the synthesized catalysts is superior to most of the reported counterparts, but with much easier preparation methods and lower production cost, making them more advantageous in practical fuel cell applications.
      Graphical abstract image Highlights A highly efficient and durable oxygen reduction reaction electrocatalyst was prepared by stabilizing the nano-sized Pt particles with a kind of defective activated carbon.

      PubDate: 2017-06-21T11:54:35Z
       
  • Hydrotalcite-wrapped Co–B alloy with enhanced oxygen evolution
           activity
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Xue Leng, Kuang-Hsu Wu, Bing-Jian Su, Ling-Yun Jang, Ian R. Gentle, Da-Wei Wang
      Water oxidation is one of the most attractive techniques for intermittent renewable energy conversion and storage. The oxygen evolution electrocatalytic performance of an amorphous Co–B alloy and its derivatives were studied. These materials were chemically synthesized by reducing a Co salt with NaBH4. The amorphous Co–B alloy showed good electrocatalytic activity in oxygen evolution but its stability was poor. A hydrotalcite-wrapped Co–B alloy was synthesized by mild oxidation. The electrocatalytic activity of this material in the oxygen evolution reaction was better than that of a commercially available Ir/C catalyst.
      Graphical abstract image

      PubDate: 2017-06-21T11:54:35Z
       
  • Highly dispersed few-layer MoS2 nanosheets on S, N co-doped carbon for
           electrocatalytic H2 production
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Shixin Hua, Dan Qu, Li An, Guangcheng Xi, Ge Chen, Fan Li, Zhijun Zhou, Zaicheng Sun
      Ultrathin small MoS2 nanosheets exhibit a higher electrocatalytic activity for the hydrogen evolution reaction. However, strong interactions between MoS2 layers may result in aggregation; together with the low conductivity of MoS2, this may lower its electrocatalytic activity. In this paper we present a method that we developed to directly produce solid S, N co-doped carbon (SNC) with a graphite structure and multiple surface groups through a hydrothermal route. When Na2MoO4 was added to the reaction, polymolybdate could be anchored into the carbon materials via a chemical interaction that helps polymolybdate disperse uniformly into the SNC. After a high temperature treatment, polymolybdate transformed into MoS2 at 800 °C for 6 h in a N2 atmosphere at a heating rate of 5 °C/min, owing to S2– being released from the SNC during the treatment (denoted as MoS2/SNC-800-6h). The SNC effectively prevents MoS2 from aggregating into large particles, and we successfully prepared highly dispersed MoS2 in the SNC matrix. Electrochemical characterizations indicate that MoS2/SNC-900-12h exhibits a low onset potential of 115 mV and a low overpotential of 237 mV at a current density of 10 mA/cm2. Furthermore, MoS2/SNC-900-12h also had an excellent stability with only ∼2.6% decay at a current density of 10 mA/cm2 after 5000 test cycles.
      Graphical abstract image

      PubDate: 2017-06-21T11:54:35Z
       
  • Fabrication, characterization and electrochemical properties of porous
           
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Qingquan Kong, Wei Feng, Xiaodong Zhu, Jing Zhang, Chenghua Sun
      In the present study, porous bulk palladium samples were prepared by sodium chloride salt powder spacer incorporation and removal combined with dealloying. The obtained porous Pd bulks were characterized by X-ray diffraction, field-emission scanning electron microscopy and N2 adsorption isotherm measurements. The prepared porous Pd bulk samples showed a hierarchical pore structure, a high porosity of ∼88%, a high surface area of ∼54 m2/g, and a compression strength of ∼0.5 MPa. Electrochemical measurements were performed to evaluate the electrocatalytic properties of the porous Pd bulk samples, revealing their effectiveness for ethanol oxidation.
      Graphical abstract image

      PubDate: 2017-06-21T11:54:35Z
       
  • Amorphous ferric oxide as a hole-extraction and transfer layer on
           nanoporous bismuth vanadate photoanode for water oxidation
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Ling Qian, Pengfei Liu, Le Zhang, Chongwu Wang, Shuang Yang, Lirong Zheng, Aiping Chen, Huagui Yang
      An amorphous ferric oxide layer was prepared on a bismuth vanadate photoanode. This resulted in improved charge carrier separation and surface catalytic performance compared with the photoanode without the oxide layer. The photocurrent of the oxide-layer-containing photoanode was 2.52 mA/cm2 at 1.23 V versus the reversible hydrogen electrode, in potassium phosphate buffer (0.5 mol/L, pH = 7.0). The amorphous ferric oxide layer on the photoanode contained low-valence-state iron species (FeII), which enabled efficient hole extraction and transfer.
      Graphical abstract image

      PubDate: 2017-06-21T11:54:35Z
       
  • Preparation of a p-n heterojunction BiFeO3@TiO2 photocatalyst with a
           core–shell structure for visible-light photocatalytic degradation
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Yazi Liu, Shanshan Ding, Jian Xu, Huayang Zhang, Shaogui Yang, Xiaoguang Duan, Hongqi Sun, Shaobin Wang
      Magnetically separable bismuth ferrite (BiFeO3) nanoparticles were fabricated by a citrate self-combustion method and coated with titanium dioxide (TiO2) by hydrolysis of titanium butoxide (Ti(OBu)4) to form BiFeO3@TiO2 core–shell nanocomposites with different mass ratios of TiO2 to BiFeO3. The photocatalytic performance of the catalysts was comprehensively investigated via photocatalytic oxidation of methyl violet (MV) under both ultraviolet and visible-light irradiation. The BiFeO3@TiO2 samples exhibited better photocatalytic performance than either BiFeO3 or TiO2 alone, and a BiFeO3@TiO2 sample with a mass ratio of 1:1 and TiO2 shell thickness of 50–100 nm showed the highest photo-oxidation activity of the catalysts. The enhanced photocatalytic activity was ascribed to the formation of a p-n junction of BiFeO3 and TiO2 with high charge separation efficiency as well as strong light absorption ability. Photoelectrochemical Mott–Schottky (MS) measurements revealed that both the charge carrier transportation and donor density of BiFeO3 were markedly enhanced after introduction of TiO2. The mechanism of MV degradation is mainly attributed to hydroxyl radicals and photogenerated electrons based on energy band theory and the formation of an internal electrostatic field. In addition, the unique core–shell structure of BiFeO3@TiO2 also promotes charge transfer at the BiFeO3/TiO2 interface by increasing the contact area between BiFeO3 and TiO2. Finally, the photocatalytic activity of BiFeO3@TiO2 was further confirmed by degradation of other industrial dyes under visible-light irradiation.
      Graphical abstract image

      PubDate: 2017-06-21T11:54:35Z
       
  • Surface-sulfurized Ag2O nanoparticles with stable full-solar-spectrum
           photocatalytic activity
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Haidong Li, Tinghan Chen, Yao Wang, Jianguo Tang, Yana Wang, Yuanhua Sang, Hong Liu
      Ag2O has attracted much recent attention, because of its high photocatalytic activity in the ultraviolet (UV)-visible region. However, there have been few reports on the near-infrared (NIR) photocatalytic activity of Ag2O. This paper reports the high NIR photocatalytic activity of Ag2O nanoparticles. Ag2O is unsuitable for application in full-solar-spectrum photocatalysis, because it is unstable under UV irradiation. A surface sulfurization process was carried out to address this issue. Specifically, a layer of Ag2S2O7 nanoparticles was grown on the surface of the Ag2O nanoparticles, to improve the stability of the Ag2O photocatalyst and enhance its photocatalytic activity in the UV, visible and NIR regions. The Ag2O/Ag2S2O7 heterostructure is a stable and efficient full-solar-spectrum photocatalyst. It has potential application in the photodegradation of organic pollutants, and more generally in environmental engineering where full utilization of the solar spectrum is required.
      Graphical abstract image

      PubDate: 2017-06-21T11:54:35Z
       
  • Synthesis of TiO2/g-C3N4 nanocomposites with phosphate–oxygen functional
           bridges for improved photocatalytic activity
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Chong Liu, Fazal Raziq, Zhijun Li, Yang Qu, Amir Zada, Liqiang Jing
      One of the most general methods to enhance the separation of photogenerated carriers for g-C3N4 is to construct a suitable heterojunctional composite, according to the principle of matching energy levels. The interface contact in the fabricated nanocomposite greatly influences the charge transfer and separation so as to determine the final photocatalytic activities. However, the role of interface contact is often neglected, and is rarely reported to date. Hence, it is possible to further enhance the photocatalytic activity of g-C3N4-based nanocomposite by improving the interfacial connection. Herein, phosphate–oxygen (P–O) bridged TiO2/g-C3N4 nanocomposites were successfully synthesized using a simple wet chemical method, and the effects of the P–O functional bridges on the photogenerated charge separation and photocatalytic activity for pollutant degradation and CO2 reduction were investigated. The photocatalytic activity of g-C3N4 was greatly improved upon coupling with an appropriate amount of nanocrystalline TiO2, especially with P–O bridged TiO2. Atmosphere-controlled steady-state surface photovoltage spectroscopy and photoluminescence spectroscopy analyses revealed clearly the enhancement of photogenerated charge separation of g-C3N4 upon coupling with the P–O bridged TiO2, resulting from the built P–O bridges between TiO2 and g-C3N4 so as to promote effective transfer of excited electrons from g-C3N4 to TiO2. This enhancement was responsible for the improved photoactivity of the P–O bridged TiO2/g-C3N4 nanocomposite, which exhibited three-time photocatalytic activity enhancement for 2,4-dichlorophenol degradation and CO2 reduction compared with bare g-C3N4. Furthermore, radical-trapping experiments revealed that the OH species formed as hole-modulated direct intermediates dominated the photocatalytic degradation of 2,4-dichlorophenol. This work provides a feasible strategy for the design and synthesis of high-performance g-C3N4-based nanocomposite photocatalysts for pollutant degradation and CO2 reduction.
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      PubDate: 2017-06-21T11:54:35Z
       
  • La1-xCaxMn1-yAlyO3 perovskites as efficient catalysts for two-step
           thermochemical water splitting in conjunction with exceptional hydrogen
           yields
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Lulu Wang, Mohammad Al-Mamun, Porun Liu, Yun Wang, Hua Gui Yang, Huijun Zhao
      Solar-driven thermochemical water splitting represents one efficient route to the generation of H2 as a clean and renewable fuel. Due to their outstanding catalytic abilities and promising solar fuel production capacities, perovskite-type redox catalysts have attracted significant attention in this regard. In the present study, the perovskite series La1-x Ca x Mn1-y Al y O3 (x, y = 0.2, 0.4, 0.6, or 0.8) was fabricated using a modified Pechini method and comprehensively investigated to determine the applicability of these materials to solar H2 production via two-step thermochemical water splitting. The thermochemical redox behaviors of these perovskites were optimized by doping at either the A (Ca) or B (Al) sites over a broad range of substitution values, from 0.2 to 0.8. Through this doping, a highly efficient perovskite (La0.6Ca0.4Mn0.6Al0.4O3) was developed, which yielded a remarkable H2 production rate of 429 μmol/g during two-step thermochemical H2O splitting, going between 1400 and 1000 °C. Moreover, the performance of the optimized perovskite was found to be eight times higher than that of the benchmark catalyst CeO2 under the same experimental conditions. Furthermore, these perovskites also showed impressive catalytic stability during two-step thermochemical cycling tests. These newly developed La1-x Ca x Mn1-y Al y O3 redox catalysts appear to have great potential for future practical applications in thermochemical solar fuel production.
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      PubDate: 2017-06-21T11:54:35Z
       
  • Acid-activated and WOx-loaded montmorillonite catalysts and their
           catalytic behaviors in glycerol dehydration
    • Abstract: Publication date: June 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 6
      Author(s): Weihua Yu, Pengpeng Wang, Chunhui Zhou, Hanbin Zhao, Dongshen Tong, Hao Zhang, Huimin Yang, Shengfu Ji, Hao Wang
      The use of H2SO4-, HCl-, H3PO4-, and CH3COOH-activated montmorillonite (Mt) and WO x /H3PO4-activated Mt as catalysts for the gas-phase dehydration of glycerol was investigated. The WO x /H3PO4-activated Mt catalysts were prepared by an impregnation method using H3PO4-activated Mt (Mt-P) as the support. The catalysts were characterized using powder X-ray diffraction, Fourier-transform infrared spectroscopy, N2 adsorption-desorption, diffuse reflectance ultraviolet-visible spectroscopy, temperature-programmed desorption of NH3, and thermogravimetric analysis. The acid activation of Mt and WO x loaded on Mt-P affected the strength and number of acid sites arising from H+ exchange, the leaching of octahedral Al3+ cations from Mt octahedral sheets, and the types of WO x (2.7 ≤ x ≤ 3) species (i.e., isolated WO4/WO6-containing clusters, two-dimensional [WO6] polytungstates, or three-dimensional WO3 crystals). The strong acid sites were weakened, and the weak and medium acid sites were strengthened when the W loading on Mt-P was 12 wt% (12%W/Mt-P). The 12%W/Mt-P catalyst showed the highest catalytic activity. It gave a glycerol conversion of 89.6% and an acrolein selectivity of 81.8% at 320 °C. Coke deposition on the surface of the catalyst led to deactivation.
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      PubDate: 2017-06-21T11:54:35Z
       
  • LSDA+U study on the electronic and anti-ferromagnetic properties of
           Ni-doped CuO and Cu-doped NiO
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Yujie Li, Fan Yang, Ying Yu
      Doping is an effective way to improve the activity of photocatalysts. The effect of doping on the magnetic properties of some photocatalysts that are easily recycled was studied using the local spin density approximation (LSDA)+U method on typical divalent metal oxide semiconductors CuO, NiO, Ni-doped CuO, and Cu-doped NiO. It is found that the influence of Ni doping on the spatial structure of CuO and that of Cu doping on the spatial structure of NiO are negligible because of the similar radii of Ni2+ and Cu2+. The valence band and conduction band for Ni-doped CuO are clearly spin-split, corresponding to a net effective magnetic moment of µ eff = 1.66 µB. This may improve the photocatalytic efficiency and raise the recycle rate of photocatalysts. In the Cu-doped NiO system, the presence of Cu 3d states near to the Fermi level increases the width of the valence band and narrows the band gap with respect to that in pure NiO. Beyond the Cu 3d states, within the band gap, appear two energy levels around the Fermi level, which may effectively separate the electron-hole pair and also lead to enhanced absorption of visible light and infrared light. It can be concluded that the observed changes in the band structure may be helpful for improving the activity of photocatalysts and the doped systems have net magnetic moments, meaning that they are easily recycled and can be reused.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Gold-catalyzed addition reaction between creatinine and isatin: A
           sustainable and green chemistry approach for the diastereoselective
           synthesis of 3-substituted-3-hydroxyisatins
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): K. Parthasarathy, T. Ponpandian, C. Praveen
      The aldolization of various isatins with creatinine under gold catalysis in water has been developed. The reaction is operationally simple as the products can be isolated by simple filtration without requiring tedious solvent extraction and column chromatographic techniques. The generality of this methodology is showcased through the reactions of a wide range of isatin derivatives with creatinine to afford the respective aldol products in excellent yields with complete syn-selectivity. The scope of this chemistry is further extended to a tandem reaction involving isatins, creatinine and malononitrile to afford multicomponent products in excellent yields with complete anti-selectivity. The antioxidant potency of the synthesized compound was assessed by a spectrophotometric method, which revealed that three compounds containing halogen atoms (2c, 2d and 2e) were the most active compared with the standard.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Enantioselective synthesis of quaternary α-aminophosphonates by
           organocatalytic Friedel–Crafts reactions of indoles with cyclic
           α-ketiminophosphonates
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Zhong Yan, Xiang Gao, Yong-Gui Zhou
      An efficient asymmetric Friedel–Crafts reaction has been developed for the synthesis of optically active quaternary α-aminophosphonates with up to 98% ee. The synthesis involves the reaction of cyclic α-ketiminophosphonates with indoles using an H8-BINOL-derived chiral phosphoric acid (CPA) catalyst that bears electron-withdrawing 3,5-ditrifluoromethylphenyl substituents on its 3- and 3′-positions. This Friedel–Crafts reaction of cyclic α-ketiminophosphonates was also successful with pyrrole.
      Graphical abstract image

      PubDate: 2017-05-22T08:35:24Z
       
  • In-plasma catalytic degradation of toluene over different MnO2 polymorphs
           and study of reaction mechanism
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Ting Wang, Si Chen, Haiqiang Wang, Zhen Liu, Zhongbiao Wu
      α-, β-, γ- and δ-MnO2 catalysts were synthesized by a one-step hydrothermal method, and were utilized for the catalytic oxidation of toluene in a combined plasma-catalytic process. The relationship between catalytic performance and MnO2 crystal structures was investigated. It was noted that the toluene removal efficiency was 32.5% at the specific input energy of 160 J/L when non-thermal plasma was used alone. The α-MnO2 catalyst showed the best activity among the investigated catalysts, yielding a toluene conversion of 78.1% at the specific input energy of 160 J/L. For β-MnO2, γ-MnO2 and δ-MnO2, removal efficiencies of 47.4%, 66.1% and 50.0%, respectively, were achieved. By powder X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy, Brunauer-Emmett-Teller, H2 temperature-programmed reduction and X-ray photoelectron spectroscopy analyses, it was concluded that the tunnel structure, the stability of the crystal in plasma, the Mn–O bond strength of MnO2 and the surface-chemisorbed oxygen species played important roles in the plasma-catalytic degradation of toluene. Additionally, the degradation routes of toluene in non-thermal plasma and in the plasma-catalytic process were also studied. It was concluded that the introduction of MnO2 catalysts enabled O3, O2, electrons and radical species in the gas to be adsorbed on the MnO2 surface via a facile interconversion among the Mn4+, Mn3+ and Mn2+ states. These four species could then be transported to the toluene or intermediate organic by-products, which greatly improved the toluene removal efficiency and decreased the final output of by-products.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Cobalt carbonyl ionic liquids based on the 1,1,3,3-tetra-alkylguanidine
           cation: Novel, highly efficient, and reusable catalysts for the
           carbonylation of epoxides
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Wei Zhang, Feng Han, Jin Tong, Chungu Xia, Jianhua Liu
      A series of novel cobalt carbonyl ionic liquids based on 1,1,3,3-tetra-alkyl-guanidine, such as [1,1-dimethyl-3,3-diethylguanidinium][Co(CO)4] (3a), [1,1-dimethyl-3,3-dibutylguanidinium][Co(CO)4] (3b), [1,1-dimethyl-3,3-tetramethyleneguanidinium][Co(CO)4] (3c), and [1,1-dimethyl-3,3-pentamethyleneguanidinium] [Co(CO)4] (3d), were synthesized in good yields and were also characterized using infrared spectroscopy, ultraviolet-visible spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy, 13C NMR spectroscopy, high–resolution mass spectrometry, differential scanning calorimetry, and thermogravimetric analysis. The four compounds exhibited high thermal and chemical stability. In addition, the catalytic performance of these compounds was investigated in the carbonylation of epoxides, with 3a exhibiting the best catalytic activity without the aid of a base as the additive. The catalyst could be reused at least six times without significant decreases of the selectivity or conversion rate. Moreover, the catalyst system exhibited good tolerance with terminal epoxides bearing alkyl, alkenyl, aryl, alkoxy, and chloromethyl functional groups.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Effect of Pd doping on CH4 reactivity over Co3O4 catalysts from
           density-functional theory calculations
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Chengcheng Zhao, Yonghui Zhao, Shenggang Li, Yuhan Sun
      Palladium oxide (PdO x ) and cobalt oxide (Co3O4) are efficient catalysts for methane (CH4) combustion, and Pd-doped Co3O4 catalysts have been found to exhibit better catalytic activities, which suggest synergism between the two components. We carried out first-principles calculations at the PBE+U level to investigate the Pd-doping effect on CH4 reactivity over the Co3O4 catalyst. Because of the structural complexity of the Pd-doped Co3O4 catalyst, we built Pd-doped catalyst models using Co3O4(001) slabs with two different terminations and examined CH4 reactivity over the possible Pd–O active sites. A low energy barrier of 0.68 eV was predicted for CH4 dissociation over the more reactive Pd-doped Co3O4(001) surface, which was much lower than the 0.98 and 0.89 eV that was predicted previously over the more reactive pure Co3O4(001) and (011) surfaces, respectively. Using a simple model, we predicted CH4 reaction rates over the pure Co3O4(001) and (011) surfaces, and Co3O4(001) surfaces with different amounts of Pd dopant. Our theoretical results agree well with the available experimental data, which suggests a strong synergy between the Pd dopant and the Co3O4 catalyst, and leads to a significant increase in CH4 reaction rate.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Facile synthesis of S-doped reduced TiO2-x with enhanced visible-light
           photocatalytic performance
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Zhenyu Huang, Zhenggang Gao, Shanmin Gao, Qingyao Wang, Zeyan Wang, Baibiao Huang, Ying Dai
      A different approach to synthesize visible-light-active sulfur (S)-doped reduced titania (S-TiO2-x ) using thiourea dioxide as both the S source and reductant was developed. The structure, morphology, and optical and electronic properties of the as-prepared S-TiO2-x samples were examined by multiple techniques, such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, Brunauer-Emmett-Teller and photocurrent measurements, and electrochemical impedance spectroscopy. The photocatalytic activity of S-TiO2-x was evaluated by photodegradation of organic Rhodamine B under visible-light irradiation. The degradation rate of Rhodamine B by S-TiO2-x obtained by calcination was about 31, 2.5, and 3.6 times higher than those of pure TiO2, pristine TiO2-x , and S-doped TiO2, respectively. In addition, the as-prepared S-TiO2-x exhibited long-term stable photocatalytic performance in the degradation of Rhodamine B under visible-light illumination. This report reveals a new approach to prepare stable and highly efficient solar light-driven photocatalysts for water purification.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Synergetic photo-epoxidation of propylene with molecular oxygen over
           bimetallic Au–Ag/TS-1 photocatalysts
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Naixu Li, Bin Yang, Ming Liu, Yong Chen, Jiancheng Zhou
      Au–Ag bimetallic nanoparticle-supported microporous titanium silicalite-1 catalysts were prepared via a hydrothermal-immersion method, and their structures were examined. These materials serve as efficient catalysts for the photosynthesis of propylene oxide via the epoxidation of propene. The Au/Ag mass ratio and reaction temperature were demonstrated to have significant effects on the catalytic activity and selectivity of propylene oxide. The optimal formation rate (68.3 μmol/g·h) and selectivity (52.3%) toward propylene oxide were achieved with an Au:Ag mass ratio of 4:1. Notably, the strong synergistic effect between Au and Ag resulted in superior photocatalysis of the bimetallic systems compared with those of the individual systems. A probable reaction mechanism was proposed based on the theoretical and experimental results.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Performance enhancement mechanism of Mn-based catalysts prepared under N2
           for NOx removal: Evidence of the poor crystallization and oxidation of
           MnOx
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Kai Qi, Junlin Xie, De Fang, Fengxiang Li, Feng He
      Among multitudinous metal-oxide catalysts for the selective catalytic reduction of NO x with NH3 (NH3-SCR), Mn-based catalysts have become very popular and developed rapidly in recent years because of its superior low-temperature denitrification activity, mainly originating from multi-valence of Mn. Most studies suggest that the catalytic activity of multi-component oxides is superior to that of single-component catalysts owing to the synergistic effect among the metallic elements in such materials, of which more attentions have been given to Ce as an additive owing to its powerful oxygen storage capacity, redox ability and its ready availability. As the core of SCR technology, the research points in catalyst development at the present stage of all researchers in countries mainly centralize on the optimization of active components, carriers, calcination temperature, calcination time and temperature-raising procedure, giving little thought to the effects of the calcination atmosphere. In the present work, Ce-modified Mn-based catalysts were prepared by a simple impregnation method. The effects of the calcination atmosphere (N2, air or O2) on the performance of the resulting materials during NH3-SCR and its causes of the differences were subsequently investigated and characterized using various analytical methods. Data obtained from X-ray diffraction, thermogravimetry and temperature-programmed reduction with hydrogen show that calcination under N2 reduces both the degree of oxidation and crystallization of the MnO x . Scanning electron microscopy also demonstrates that the use of N2 inhibits the growth of grains and increases the dispersion of the catalysts. In addition, the results of temperature-programmed desorption with ammonia indicate that catalysts calcined under N2 exhibit a greater quantity of acid sites. Finally, X-ray photoelectron spectrometry and activity results demonstrate that MnO x in the lower valence states is more favorable for NH3-SCR reactions. In conclusion, catalysts calcined under N2 show superior performance during NH3-SCR for NO x removal, allowing NO conversions up to 94% at 473 K.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Brønsted-acidic ionic liquids as efficient catalysts for the synthesis of
           polyoxymethylene dialkyl ethers
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Heyuan Song, Meirong Kang, Fuxiang Jin, Guoqin Wang, Zhen Li, Jing Chen
      Acetalation of formaldehyde (HCHO) with dialkyl formal or aliphatic alcohol to prepare polyoxymethylene dialkyl ethers (RO(CH2O) n R, n ≥ 1) catalyzed by Brønsted-acidic ionic liquids has been developed. The correlation between the structure and acidity activity of various ionic liquids was studied. Among the ionic liquids investigated, 1-(4-sulfonic acid)butyl-3-methylimidazolium hydrogen sulfate ([MIMBs]HSO4) exhibited the best catalytic performance in the reaction of diethoxymethane (DEM1) with trioxane. The influences of ionic liquid loading, molar ratio of DEM1 to HCHO, reaction temperature, pressure, time, and reactant source on the catalytic reaction were explored using [MIMBs]HSO4 as the catalyst. Under the optimal conditions of n([MIMBs]HSO4):n(DEM1):n(HCHO) = 1:80:80, 140 °C, and 4 h, the conversion of HCHO and selectivity for DEM2–8 were 92.6% and 95.1%, respectively. The [MIMBs]HSO4 catalyst could be easily separated and reused. A feasible mechanism for the catalytic performance of [MIMBs]HSO4 was proposed.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Quaternary-ammonium-immobilized polystyrenes as efficient and reusable
           heterogeneous catalysts for synthesis of cyclic carbonate: Effects of
           linking chains and pendent hydroxyl group
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Xiaoming Yan, Xuan Ding, Yu Pan, Xiaowei Xu, Ce Hao, Wenji Zheng, Gaohong He
      Spherical polystyrene-supported ammonium salts containing different linking chains between the support and ammonium groups were prepared as efficient and easily reusable heterogeneous catalysts for the cycloadditions of CO2 and epoxides. The effects of the length of the linking chains and a hydroxyl group pendent on the linking chain on the catalytic performance of ionic liquid immobilized catalysts and their mechanisms were studied through experiments and density functional theory calculations. It was found that, compared with a short linking chain, a long chain can make the halogen anion more negative and provide a larger contact area of the catalysts with the reactants, thus enhancing the reaction kinetics. The hydroxyl group can stretch the C–O bonds of the epoxides, promoting the reaction thermodynamics. As a result, for the cycloaddition of propylene oxide, the yield of propylene carbonate is much higher for the catalyst with a long linking chain (yield: 91.4%) compared with the yield for that with a short chain (yield: 70.9%), and is further increased in the presence of pendent hydroxyl groups (yield: 98.5%). The catalyst also shows a high catalytic activity even at mild temperature and good reusability (yield: ≥ 96% for 10 cycles), and the selectivity is always above 99%.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Synthesis of ZSM-5 monoliths with hierarchical porosity through a
           steam-assisted crystallization method using sponges as scaffolds
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Tiejing Hu, Jian Liu, Changyan Cao, Weiguo Song
      Self-supporting ZSM-5 crystals with hierarchical porosity were prepared through a steam-assisted crystallization method using sponges as rigid scaffolds. The synthesized materials were characterized by X-ray diffraction, nitrogen sorption, scanning electron microscopy, transmission electron microscopy, solid-state nuclear magnetic resonance spectroscopy and ammonia temperature-programmed desorption. The ZSM-5 monoliths exhibited high crystallinities, hierarchical porous structures and strong acidities. They showed superior catalytic performance in the liquid-phase esterification reaction between benzyl alcohol and hexanoic acid.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Synthesis of propylene glycol ethers from propylene oxide catalyzed by
           environmentally friendly ionic liquids
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Cong Zhao, Shengxin Chen, Ruirui Zhang, Zihang Li, Ruixia Liu, Baozeng Ren, Suojiang Zhang
      A series of acetate ionic liquids were synthesized using a typical two-step method. The ionic liquids were used as environmentally benign catalysts in the production of propylene glycol ethers from propylene oxide and alcohols under mild conditions. The basic strengths of the ionic liquids were evaluated by determination of their Hammett functions, obtained using ultraviolet-visible spectroscopy, and the relationship between their catalytic activities and basicities was established. The catalytic efficiencies of the ionic liquids were higher than that of the traditional basic catalyst NaOH. This can be attributed to the involvement of a novel reaction mechanism when these ionic liquids are used. A possible electrophilic-nucleophilic dual activation mechanism was proposed and confirmed using electrospray ionization quadrupole time-of-flight mass spectrometry. In addition, the effects of significant reaction parameters such as concentration of catalyst, molar ratio of alcohol to propylene oxide, reaction temperature, and steric hindrance of the alcohol were investigated in detail.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Chiral BINAP-based hierarchical porous polymers as platforms for efficient
           heterogeneous asymmetric catalysis
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Tao Wang, Yuan Lyu, Kai Xiong, Wenlong Wang, Hao Zhang, Zhuangping Zhan, Zheng Jiang, Yunjie Ding
      Two vinyl-functionalized chiral 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) ligands, (S)-4,4′-divinyl-BINAP and (S)-5,5′-divinyl-BINAP, were successfully synthesized. Chiral BINAP-based porous organic polymers (POPs), denoted as 4-BINAP@POPs and 5-BINAP@POPs, were efficiently prepared via the copolymerization of vinyl-functionalized BINAP with divinyl benzene under solvothermal conditions. Thorough characterization using nuclear magnetic resonance spectroscopy, thermogravimetric analysis, extended X-ray absorption fine structure analysis, and high-angle annular dark-field scanning transmission electron microscopy, we confirmed that chiral BINAP groups were successfully incorporated into the structure of the materials considered to contain hierarchical pores. Ru was introduced as a catalytic species into the POPs using different synthetic routes. Systematic investigation of the resultant chiral Ru/POP catalysts for heterogeneous asymmetric hydrogenation of β-keto esters revealed their excellent chiral inducibility as well as high activity and stability. Our work thereby paves a path towards the use of advanced hierarchical porous polymers as solid chiral platforms for heterogeneous asymmetric catalysis.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Sr-doping effects on La2O3 catalyst for oxidative coupling of methane
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Linna Cong, Yonghui Zhao, Shenggang Li, Yuhan Sun
      Density-functional theory calculations were carried out to study the strontium (Sr)-doping effect on methane activation over a lanthanum-oxide (La2O3) catalyst for the oxidative coupling of methane (OCM) using the cluster model. Eight Sr-doped La2O3 cluster models were built from pure La2O3 clusters that were used previously to model the La2O3 catalyst. These form two distinct categories, namely, those without a radical character (LaSrO2(OH), La2SrO4, La3SrO5(OH), and La5SrO8(OH)) and those with a radical character (LaSrO3, La2SrO4(OH), La3SrO6, and La5SrO9). The potential-energy surface for CH4 activation to form a CH3 radical at different Sr–O and La–O pair sites on these Sr-doped La2O3 clusters was calculated to study the Sr-doping effect on the OCM catalytic activity. CH4 physisorption and chemisorption energies, and activation barriers, and CH3 desorption energies were predicted. Compared with the pure La2O3 clusters, in general, the Sr-doped La2O3 clusters are thermodynamically and kinetically more reactive with CH4. For the Sr-doped La2O3 clusters without the radical character, the Sr–O pair site is more reactive with CH4 than the La–O pair site, although a direct release of the CH3 radical is also highly endothermic as in the case of the pure La2O3 clusters. In contrast, for the Sr-doped La2O3 clusters with a radical character, the activation of CH4 at the oxygen radical site and the release of the CH3 radical are much easier. Thus, our calculations suggest that the Sr dopant prompts the OCM catalytic activity of the La2O3 catalyst by providing a highly active oxygen-radical site and by strengthening the basicity of the M–O pair site, which leads to lower CH4 activation energies and lower CH3 desorption energies.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Synthesis of isosorbide-based polycarbonates via melt polycondensation
           catalyzed by quaternary ammonium ionic liquids
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Wei Sun, Fei Xu, Weiguo Cheng, Jian Sun, Guoqing Ning, Suojiang Zhang
      A series of quaternary ammonium ionic liquids (ILs) were synthesized and employed as catalysts for the production of poly(isosorbide carbonate) (PIC) from diphenyl carbonate and isosorbide via a melt polycondensation process. The relationship between the anions of the ILs and the catalytic activities was investigated, and the readily-prepared IL tetraethylammonium imidazolate (TEAI) was found to exhibit the highest catalytic activity. After optimizing the reaction conditions, a PIC with a weight-average molecular weight (M w) of 25600 g/mol was obtained, in conjunction with an isosorbide conversion of 92%. As a means of modifying the molecular flexibility and thermal properties of the PIC, poly(aliphatic diol-co-isosorbide carbonate)s (PAIC)s were successfully synthesized, again using TEAI, and polymers with M w values ranging from 29000 to 112000 g/mol were obtained. 13C NMR analyses determined that the PAIC specimens had random microstructures, while differential scanning calorimetry demonstrated that each of the PAICs were amorphous and had glass transition temperatures ranging from 50 to 115 °C. Thermogravimetric analyses found T d-5% values ranging from 316 to 332 °C for these polymers. Based on these data, it is evident that the incorporation of linear or cyclohexane-based diol repeating units changed the thermal properties of the PIC.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Investigation of low-temperature hydrothermal stability of Cu-SAPO-34 for
           selective catalytic reduction of NOx with NH3
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Xiao Xiang, Pengfei Wu, Yi Cao, Lei Cao, Quanyi Wang, Shutao Xu, Peng Tian, Zhongmin Liu
      The low-temperature hydrothermal stabilities of Cu-SAPO-34 samples with various Si contents and Cu loadings were systematically investigated. The NH3 oxidation activities and NH3-selective catalytic reduction (SCR) activities (mainly the low-temperature activities) of all the Cu-SAPO-34 catalysts declined after low-temperature steam treatment (LTST). These results show that the texture and acid density of Cu-SAPO-34 can be better preserved by increasing the Cu loading, although the hydrolysis of Si–O–Al bonds is inevitable. The stability of Cu ions and the stability of the SAPO framework were positively correlated at relatively low Cu loadings. However, a high Cu loading (e.g., 3.67 wt%) resulted in a significant decrease in the number of isolated Cu ions. Aggregation of CuO particles also occurred during the LTST, which accounts for the decreasing NH3 oxidation activities of the catalysts. Among the catalysts, Cu-SAPO-34 with a high Si content and medium Cu content (1.37 wt%) showed the lowest decrease in NH3-SCR because its Cu2+ content was well retained and its acid density was well preserved.
      Graphical abstract image

      PubDate: 2017-05-22T08:35:24Z
       
  • One-step synthesis of pyruvic acid from glycerol oxidation over Pb
           promoted Pt/activated carbon catalysts
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Chen Zhang, Tao Wang, Yunjie Ding
      One-step production of pyruvic acid through selective oxidation of glycerol was investigated using lead promoted platinum/activated carbon (Pb-Pt/AC) catalysts under mild conditions. The results of N2 physisorption, X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy revealed that the alloy phases of PtPb and Pt x Pb were favorable for pyruvic acid production from glycerol oxidation, whereas the Pb3(CO3)2(OH)2 and surface Pb0 species inhibited the glycerol conversion. The loading of Pb and the catalyst preparation method (including impregnation and deposition precipitation) affected the formation of different metal species. Pyruvic acid was obtained at a yield of 18.4% on a 5.0 wt% Pb-5.0 wt% Pt/AC catalyst prepared by co-deposition precipitation method and 500 °C argon treatment.
      Graphical abstract image

      PubDate: 2017-05-22T08:35:24Z
       
  • Enhancement of the formic acid electrooxidation activity of palladium
           using graphene/carbon black binary carbon supports
    • Abstract: Publication date: May 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 5
      Author(s): Meiying Lv, Wenpeng Li, Huiling Liu, Wenjuan Wen, Guang Dong, Jinghua Liu, Kaichen Peng
      Combinations of graphene (Gr) and carbon black (C) were employed as binary carbon supports to fabricate Pd-based electrocatalysts via one-pot co-reduction with Pd2+. The electrocatalytic performance of the resulting Pd/Gr-C catalysts during the electrooxidation of formic acid was assessed. A Pd/Gr0.3C0.7 (Gr oxide:C = 3:7, based on the precursor mass ratio) electrocatalyst exhibited better catalytic performance than both Pd/C and Pd/Gr catalysts. The current density generated by the Pd/Gr0.3C0.7 catalyst was as high as 102.14 mA mgPd −1, a value that is approximately 3 times that obtained from the Pd/C (34.40 mA mgPd −1) and 2.6 times that of the Pd/Gr material (38.50 mA mgPd −1). The anodic peak potential of the Pd/Gr0.3C0.7 was 120 mV more negative than that of the Pd/C and 70 mV more negative than that of the Pd/Gr. Scanning electron microscopy images indicated that the spherical C particles accumulated on the wrinkled graphene surfaces to form C cluster/Gr hybrids having three-dimensional nanostructures. X-ray photoelectron spectroscopy data confirmed the interaction between the Pd metal and the binary Gr-C support. The Pd/Gr0.3C0.7 also exhibited high stability, and so is a promising candidate for the fabrication of anodes for direct formic acid fuel cells. This work demonstrates a simple and cost-effective method for improving the performance of Pd-based electrocatalysts, which should have potential industrial applications.
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      PubDate: 2017-05-22T08:35:24Z
       
  • Engineering vacancies for solar photocatalytic applications
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Mingce Long, Longhui Zheng
      In contrast to the exploration of novel photocatalytic materials, vacancy engineering of traditional photocatalysts comprising earth-abundant elements represents an effective method for enhancing photocatalytic performance without introducing alien elements. This minireview analyzes the latest progress in engineering vacancies in photocatalysts, remarks on state-of-the-art characterization techniques for vacancies, and reviews the formation chemistry and fundamental benefits of anion and cation vacancies in typical photocatalysts. Although knowledge of these vacancies is increasing, challenges remain in this field, and possible further research is therefore also discussed.
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      PubDate: 2017-04-24T03:30:11Z
       
  • Selective aerobic oxidation promoted by highly efficient multi-nitroxy
           organocatalysts
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Kexian Chen, Haiying Xie
      Selective oxidation with molecular oxygen as the sole oxidant under mild conditions is of crucial importance for the long-term sustainable exploitation of available feedstocks and the formation of required intermediates for organic synthesis and industrial processes. Among the developed oxidation protocols, innovative strategies using hydroxyimide organocatalysts in combination with metallic or metal-free cocatalysts have attracted much attention because of the good activities and selectivities of such catalysts in the oxo functionalization of hydrocarbons. This method is based on the reaction using N-hydroxyphthalimide, which was first reported by Ishii's group in the 1990s. Although the important and wide-ranging applications of such catalysts have been summarized recently, there are no reviews that focus solely on oxidation strategies using multi-nitroxy organocatalysts, which have interesting properties and high reactivities. This review covers the concise synthetic methods and mechanistic profiles of known multi-nitroxy organocatalysts and summarizes significant advances in their use in efficient aerobic oxidation. Based on a combination of experimental and theoretical results, guidelines for the future rational design of multi-nitroxy organocatalysts are proposed, and the properties of various model multi-nitroxy organocatalysts are predicted. The present overview of the advantages, limitations, and potential applications of multi-nitroxy organocatalysts can provide useful tools for researchers in the field of selective oxidation.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Supercritical synthesis of platinum-modified titanium dioxide for solar
           fuel production from carbon dioxide
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Susana Tostón, Rafael Camarillo, Fabiola Martínez, Carlos Jiménez, Jesusa Rincón
      This paper investigates the properties of TiO2-based photocatalysts synthesised under supercritical conditions. Specifically, the characteristics of Pt dispersed on TiO2 catalysts obtained in supercritical CO2 are discussed and compared with those of commercial TiO2. The photocatalytic activity of the synthesised catalysts in the CO2 photoreduction reaction to produce solar fuel is tested. The main conclusion of the study is that photocatalysts with better or similar features, including high surface area, crystallisation degree, hydroxyl surface concentration, pore volume, absorbance in the visible range and methane production rate, to those of commercial TiO2 may be produced for the reduction of CO2 to fuel by synthesis in supercritical media.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Simple synthesis of sub-nanometer Pd clusters: High catalytic activity of
           Pd/PEG-PNIPAM in Suzuki reaction
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Zhe Chen, Yu Liang, Da-Shuang Jia, Zhi-Min Cui, Wei-Guo Song
      Ultra-small metal nanoclusters have high surface energy and abundant active sites, and therefore their catalytic activities are usually significantly higher than those of larger nanoparticles. A temperature-responsive copolymer, namely poly(ethylene glycol)-co-poly(N-isopropylacrylamide) (PEG-PNIPAM) was synthesized as the first step, and then ultra-small Pd clusters stabilized within PEG-PNIPAM copolymer micelles were formed by direct reduction. Pd nanoclusters of size less than 2 nm showed outstanding catalytic activity in the Suzuki coupling reaction. The reaction between iodobenzene and phenylboronic acid was completed in as little as 10 s (turnover frequency = 4.3 × 104 h−1). A yield of 64% was achieved in 5 min in the reaction between chlorobenzene and phenylboronic acid. The catalyst showed significant deactivation during three consecutive runs. However, this composite catalyst consisting of Pd/PEG-PNIPAM can be easily recycled based on the reversible phase transition of temperature-responsive PEG-PNIPAM. This catalyst therefore has good potential for practical applications.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Cu2O/SiC as efficient catalyst for Ullmann coupling of phenols with aryl
           halides
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Yibing Wang, Xiaoning Guo, Manqian Lü, Zhaoyang Zhai, Yingyong Wang, Xiangyun Guo
      A Cu2O/SiC heterogeneous catalyst was prepared via a two-step liquid-phase method using diethylene glycol as both the solvent and the reducing agent. The catalyst was characterized using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and H2 temperature-programmed reduction. All the results indicate that Cu is present on the SiC support primarily as Cu2O. The SEM and TEM results show that cubic Cu2O nanoparticles are uniformly dispersed on the β-SiC surface. The reaction conditions, namely the temperature, reaction time, and amounts of base and catalyst used, for the Ullmann-type C–O cross-coupling reaction were optimized. A model reaction was performed using iodobenzene (14.0 mmol) and phenol (14.0 mmol) with Cu2O/SiC (5 wt% Cu) as the catalyst, Cs2CO3 (1.0 equiv.) as the base, and tetrahydrofuran as the solvent at 150 °C for 3 h; a yield of 97% was obtained and the turnover frequency (TOF) was 1136 h−1. The Cu2O/SiC catalyst has a broad substrate scope and can be used in Ullmann-type C–O cross-coupling reactions of aryl halides and phenols bearing a variety of different substituents. The catalyst also showed high activity in the Ullmann-type C–S cross-coupling of thiophenol with iodobenzene and substituted iodobenzenes; a TOF of 1186 h−1 was achieved. The recyclability of the Cu2O/SiC catalyst in the O-arylation of phenol with iodobenzene was investigated under the optimum conditions. The yield decreased from 97% to 64% after five cycles. The main reason for the decrease in the catalyst activity is loss of the active component, i.e., Cu2O.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Purification and characterization of alkaline chitinase from Paenibacillus
           pasadenensis CS0611
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Xiaoxiao Guo, Pei Xu, Minhua Zong, Wenyong Lou
      An extracellular chitinase produced by Paenibacillus pasadenensis CS0611 was purified by ammonium sulfate precipitation, HiTrap DEAE FF and HiLoad 26/600 Superdex 200pg column chromatography. The apparent molecular mass determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis was 69 kDa. The optimum pH and optimum temperature of the chitinase were 5.0 and 50 °C, respectively. The enzyme showed high stability at alkaline pH values and temperatures below 40 °C. Additionally, the metal ions Mn2+, Mg2+, and Co2+ inhibited activity of the chitinase. The chitinase was active on colloidal chitin with an apparent K m of 4.41 mg/mL and V max of 1.08 mg/min. Substrate spectrum analysis indicated that the chitinase reacted preferentially with the glucosidic bond between GlcNAc-GlcNAc. The enzymatic hydrolysate was analyzed by high-performance liquid chromatography and thin layer chromatography, and clearly showed that a subunit of (GlcNAc)2 was the main hydrolysis product.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Fe, N, S-doped porous carbon as oxygen reduction reaction catalyst in
           acidic medium with high activity and durability synthesized using CaCl2 as
           template
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Chi Chen, Zhiyou Zhou, Yucheng Wang, Xue Zhang, Xiaodong Yang, Xinsheng Zhang, Shigang Sun
      Proton exchange membrane fuel cells suffer from the sluggish kinetics of the oxygen reduction reaction (ORR) and the high cost of Pt catalysts. In the present work, a high-performance ORR catalyst based on Fe, N, S-doped porous carbon (FeNS-PC) was synthesized using melamine formaldehyde resin as C and N precursors, Fe(SCN)3 as Fe and S precursors, and CaCl2 as a template via a two-step heat treatment without a harsh template removal step. The results show that the catalyst treated at 900 °C (FeNS-PC-900) had a high surface area of 775 m2/g, a high mass activity of 10.2 A/g in an acidic medium, and excellent durability; the half-wave potential decreased by only 20 mV after 10000 potential cycles. The FeNS-PC-900 catalyst was used as the cathode in a proton exchange membrane fuel cell and delivered a peak power density of 0.49 W/cm2. FeNS-PC-900 therefore has good potential for use in practical applications.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Correlation between H-ZSM-5 crystal size and catalytic performance in the
           methanol-to-aromatics reaction
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Lingzhi Yang, Zhiyuan Liu, Zhi Liu, Wenyong Peng, Yunqi Liu, Chenguang Liu
      The porosity of H-ZSM-5 zeolite is known to facilitate the diffusion of molecules in the methanol-to-aromatics (MTA) reaction. The activity and selectivity of the H-ZSM-5 catalyst in the MTA reaction has been studied as a function of crystal size. ZSM-5 zeolites with different crystal sizes were successfully synthesized by conventional hydrothermal methods. Tailoring ZSM-5 particle size was easily controlled by changes to the sol-gel composition, and in particular, the deionized water to tetrapropylammonium hydroxide ratio, and crystallization time. The structure of the H-ZSM-5 zeolites were characterized by X-ray diffraction and the morphology of the zeolite particles was determined by scanning electron microscopy. N2 adsorption-desorption measurements established changes to the textural properties, and compositional properties were characterized by X-ray fluorescence spectroscopy. Acidity measurements of the catalysts were measured by pyridine-adsorbed Fourier transform infrared spectroscopy and the temperature-programmed desorption of ammonia. After subjecting the catalysts to the MTA reaction, the total amount of coke formed on the spent deactivated catalysts was determined by thermal gravimetric analysis. The results show that the SiO2/Al2O3 molar ratios and acidic properties of the H-ZSM-5 samples are similar, however, the nano-sized hierarchical ZSM-5 zeolite with an additional level of auxiliary pores possesses a higher surface area, larger mesopore volume and larger macropore volume, resulting in more effective mass transportation properties. The H-ZSM-5 zeolite catalysts were evaluated for their activity towards the MTA reaction as a function of crystal size. The nano-sized H-ZSM-5 catalyst having shorter diffusion path lengths, substantial mesoporosity and a high external surface area showed excellent selectivity toward aromatics (average > 42%) and benzene, toluene and xylenes (37% at 180 min). Furthermore, lower coking levels were observed on the nano-sized H-ZSM-5 catalyst when compared with the H-ZSM-5 catalysts possessing larger particle sizes and is attributed to a reduction in polyaromatic hydrocarbons being deposited within the internal surface area.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Porous Rh/BINAP polymers as efficient heterogeneous catalysts for
           asymmetric hydroformylation of styrene: Enhanced enantioselectivity
           realized by flexible chiral nanopockets
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Tao Wang, Wenlong Wang, Yuan Lyu, Kai Xiong, Cunyao Li, Hao Zhang, Zhuangping Zhan, Zheng Jiang, Yunjie Ding
      A new chiral monomer, (S)-5,5′-divinyl-BINAP, was successfully synthesized and embedded into two different porous organic polymers (Poly-1 and Poly-2). After loading a Rh species, the catalysts were applied for the heterogeneous asymmetric hydroformylation of styrene. Compared with the homogeneous BINAP analogue, the enantioselectivity of Rh/Poly-1 catalyst was drastically increased by approximately 70%. The improved enantioselectivity of the porous Rh/BINAP polymers was attributed to the presence of flexible chiral nanopockets resulting from the increased bulk of the R groups near the catalytic center.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Influence of supports for selective production of 2,5-dimethylfuran via
           
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Sanjay Srivastava, G.C. Jadeja, Jigisha Parikh
      The hydrogenolysis of carbon–oxygen bonds is an important model reaction in upgrading biomass-derived furanic compounds to transportation fuels. One of these model reactions, namely conversion of 5-hydroxymethylfurfural (HMF) to the gasoline additive 2,5-dimethylfuran (DMF), is especially attractive. In this study, bimetallic Cu-Co catalysts supported on CeO2, ZrO2, and Al2O3 were used for the selective hydrogenolysis of HMF to DMF. The structures of the fresh and used catalysts were studied using X-ray diffraction, the Brunauer-Emmett-Teller method, transmission electron microscopy, temperature-programmed reduction by H2, temperature-programmed desorption of NH3, and CHNS analysis. The structures were correlated with the catalytic activities. The Cu-Co/CeO2 catalyst produced mainly 2,5-bis(hydroxymethyl)furan via reduction of C=O bonds on large Cu particles. The Cu-Co/Al2O3 catalyst gave the best selectivity for DMF, as a result of a combination of highly dispersed Cu, mixed copper–cobalt oxides, and suitable weak acidic sites. Cu-Co/ZrO2 had low selectivity for DMF and produced a combination of various over-hydrogenolysis products, including 2,5-dimethyltetrahydrofuran and 5,5-oxybis(methylene)-bis(2-methylfuran), because of the presence of strong acidic sites. The reaction pathways and effects of various operating parameters, namely temperature, H2 pressure, and time, were studied to enable optimization of the selective conversion of HMF to DMF over the Cu-Co/Al2O3 catalyst.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Synthesis, characterization and application of BiVO4 photoanode for
           photoelectrochemical oxidation of chlorate
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Seyed Ghorban Hosseini, Saeid Safshekan
      A high-quality polycrystalline bismuth vanadate (BiVO4) film was prepared on a fluorine-doped tin oxide substrate via a facile two-step strategy involving electrodeposition and annealing processes. The morphology and structural characterization of the resulting film were investigated by different methods including scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), and Fourier transform infrared, ultraviolet-visible (UV-vis) absorption, and Raman spectroscopies. XRD patterns as well as optical measurements revealed that BiVO4 film crystallized with a pure monoclinic scheelite structure. The prepared BiVO4 film was used for heterogeneous oxidation of chlorate ions in aqueous solution via electrochemical (EC), photochemical (PC), and photoelectrochemical (PEC) processes. The decrease in concentration of chlorate was monitored using UV-vis absorption spectroscopy. The results revealed that BiVO4 could effectively perform chlorate oxidation under light irradiation through a PEC method. The kinetics of chlorate oxidation was consistent with a first-order reaction, and the rate constant for the PEC process was found to be much higher than those of EC and PC. Furthermore, a possible photocatalytic oxidation mechanism for chlorate mainly based on the formation of perchlorate ions is proposed.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • CO2 hydrogenation to methanol over Cu/Zn/Al/Zr catalysts prepared by
           liquid reduction
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Xiaosu Dong, Feng Li, Ning Zhao, Yisheng Tan, Junwei Wang, Fukui Xiao
      Cu/Zn/Al/Zr catalysts containing Cu in three valence states (Cu2+, Cu+ and Cu0) were prepared using a liquid reduction method and subsequently calcined at different temperatures. The effects of the calcination temperature on the catalyst structure, interactions among components, reducibility and dispersion of Cu species, surface properties and exposed Cu surface area were systematically investigated. These materials were also applied to the synthesis of methanol via the hydrogenation of CO2. The results show that a large exposed Cu surface area promotes catalytic CO2 conversion and that there is a close correlation between the Cu+/Cu0 ratio and the selectivity for methanol. A calcination temperature of 573 K was found to produce a Cu/Zn/Al/Zr catalyst exhibiting the maximum activity during the synthesis of methanol.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Ordered mesoporous Sn-SBA-15 as support for Pt catalyst with enhanced
           performance in propane dehydrogenation
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Bing Li, Zhenxin Xu, Wei Chu, Shizhong Luo, Fangli Jing
      A series of Sn-incorporated SBA-15 materials with high specific surface areas and highly ordered mesoporous structures were synthesized by a facile one-pot method and used as catalyst supports. A reference sample was also prepared using a conventional impregnation method. The catalysts were characterized using various methods, and their activities in propane dehydrogenation were investigated. The incorporation of Sn into the SBA-15 matrix led to strong interactions between Sn species and the support, and these helped to maintain the oxidation states of Sn species during the reaction. Substitution with Sn changed the interfacial properties of the Pt species and improved the function and effect of the Sn promoter. The catalytic activities and stabilities of the Pt catalysts supported on Sn-incorporated SBA-15 were better than those of the impregnated sample. However, the catalytic performance deteriorated when an excessive amount of Sn was introduced and the interactions among Pt, Sn species, and the support became weaker. The Pt/0.5Sn-SBA-15 catalyst gave the best propene selectivity, i.e., 98.5%, with a corresponding propane conversion of about 43.8%.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Transformation of carbon dioxide into valuable chemicals over bifunctional
           metallosalen catalysts bearing quaternary phosphonium salts
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Wuying Zhang, Rongchang Luo, Qihang Xu, Yaju Chen, Xiaowei Lin, Xiantai Zhou, Hongbing Ji
      The chemical transformation of CO2 under mild conditions remains a great challenge because of its exceptional kinetic and thermodynamic stability. Two important reactions in the transformation of CO2 are the N-formylation reaction of amines using hydrosilanes and CO2, and the cycloaddition of CO2 to epoxides. Here, we report the high efficiency of bifunctional metallosalen complexes bearing quaternary phosphonium salts in catalyzing both of these reactions under solvent-free, mild conditions without the need for co-catalysts. The catalysts' bifunctionality is attributed to an intramolecular cooperative process between the metal center and the halogen anion. Depending on the reaction, this activates CO2 by permitting either the synergistic activation of Si–H bond via metal–hydrogen coordinative bond (M–H) or the dual activation of epoxide via metal–oxygen coordinative bond (M–O). The one-component catalysts are also shown to be easily recovered and reused five times without significant loss of activity or selectivity. The current results are combined with previous work in the area to propose the relevant reaction mechanisms.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Nanoscale graphene oxide sheets as highly efficient carbocatalysts in
           green oxidation of benzylic alcohols and aromatic aldehydes
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Alireza Sedrpoushan, Masoud Heidari, Omid Akhavan
      Nanoscale graphene oxide (NGO) sheets were synthesized and used as carbocatalysts for effective oxidation of benzylic alcohols and aromatic aldehydes. For oxidation of alcohols in the presence of H2O2 at 80 °C, the NGOs (20% mass fraction) as carbocatalysts showed selectivity toward aldehyde. The rate and yield of this reaction strongly depended on the nature of substituents on the alcohol. For 4-nitrobenzyl alcohol, <10% of it was converted into the corresponding carboxylic acid after 24 h. By contrast, 4-methoxybenzyl alcohol and diphenylmethanol were completely converted into the corresponding carboxylic acid and ketone after only 9 and 3 h, respectively. The conversion rates for oxidation of aromatic aldehydes by NGO carbocatalysts were higher than those for alcohol oxidation. For all the aldehydes, complete conversion to the corresponding carboxylic acids was achieved using 7% (mass fraction) of NGO at 70 °C within 2–3 h. Possible mechanisms for NGO carbocatalyst structure-dependent oxidation of benzyl alcohols and structure-independent oxidation of aromatic aldehydes are discussed.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
  • Zirconium triflate grafted on SBA-15 as a highly efficient solid acid
           catalyst for ring opening of epoxides by amines and alcohols
    • Abstract: Publication date: April 2017
      Source:Chinese Journal of Catalysis, Volume 38, Issue 4
      Author(s): Kamlesh N. Tayade, Lianyue Wang, Sensen Shang, Wen Dai, Manish Mishra, Shuang Gao
      Metal (Al, Ti, Zr) triflate grafted mesoporous SBA-15 (AlTf/S, TiTf/S, ZrTf/S) samples were synthesized as inexpensive solid acid materials by a simple one-pot-two-step synthesis methodology. These materials were characterized by X-ray diffraction, N2-sorption, thermogravimetric analysis, Fourier transform infrared spectroscopy (FT-IR), in-situ pyridine FT-IR spectroscopy, and elemental analysis. ZrTf/S was found to be a highly efficient and reusable solid acid catalyst for ring opening of epoxides with amines and alcohols and produced β-amino alcohols and β-alkoxy alcohols respectively under ambient reaction conditions. The ZrTf/S catalyst showed the highest activity, which was attributed to its high acidity compared with that of the Ti and Al containing samples.
      Graphical abstract image

      PubDate: 2017-04-24T03:30:11Z
       
 
 
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