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  Subjects -> ENGINEERING (Total: 2312 journals)
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ENGINEERING (1213 journals)                  1 2 3 4 5 6 7 | Last

Showing 1 - 200 of 1205 Journals sorted alphabetically
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Chaos : An Interdisciplinary Journal of Nonlinear Science     Hybrid Journal   (Followers: 2)
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Journal Cover Catalysis Today
  [SJR: 1.348]   [H-I: 164]   [7 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0920-5861
   Published by Elsevier Homepage  [3123 journals]
  • Zeolite constructor kit: Design for catalytic applications
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): M. Opanasenko
      Pure microporosity of conventional zeolites is a disadvantage for the processes required enhanced accessibility that can be overcome by the design of mesoporous or hierarchical zeolites. Approaches for development of additional porosity in zeolite materials including diverse bottom-up and top-down strategies are considered and compared in this paper. Zeolites are presented as construction kits to produce more open and hence active materials for catalytic applications. This review focuses on the understanding of advantages and limitations of each synthesis approach. The advances in design of hierarchical materials as catalysts are exemplified by comparison with bulk analogues. The possibilities for encapsulation of nanoparticles in microporous or hierarchical zeolitic frameworks are also assessed.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • The Lewis acidity of three- and two-dimensional zeolites: The effect of
           framework topology
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Thang Viet Ho, Petr Nachtigall, Lukáš Grajciar
      The zeolite activity in processes driven by Lewis acid sites is determined by the distribution of the extra-framework cations in the zeolite and their coordination with the framework (the stronger is the cation coordination, the weaker is its Lewis acidity). This study aims to test how much the transformation from 3D zeolite to its corresponding 2D layered form changes the extra-framework cation distribution and coordination and thus how much it affects the zeolite Lewis acid strength. Zeolites with two distinct topologies, MWW and MFI, which form layers with considerably different silanol density (1.1 and 2.9 silanols/nm2, respectively) were considered. To probe the Lewis acidity of extra-framework Li+ sites the carbon monoxide stretching frequencies and adsorption enthalpies were calculated, employing the dispersion-corrected density functional theory and the results are in good agreement with available experimental data. No or negligible differences in the Lewis acidity of Li+ sites in 2D and 3D form of zeolites with MWW topology are found; both, the extra-framework cation distribution and the coordination with the framework remain the same. On the contrary, there are significant differences in Lewis acidic properties of 3D and 2D zeolites with MFI topology. The Li+ cation coordination in 2D-MFI is considerably improved compared to 3D-MFI due to the large concentration of surface silanols and due to an increased flexibility of the material. Consequently, Lewis acidity of 2D-MFI is lower compared to corresponding 3D-MFI material. This Lewis acidity decrease also reflects the fact that the strongest Lewis acid sites found in 3D zeolite − the channel-intersection sites (coordinated with two framework oxygens only) − are not present in 2D-MFI. The results reported herein suggest that the flexibility of the layer, which increases with silanol density and varies for each zeolite topology, significantly influences its Lewis acidity; the larger is the flexibility of the layer, the better is the cation coordination with the framework and thus smaller is its Lewis acidity.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • The effect of hot liquid water treatment on the properties and catalytic
           activity of MWW zeolites with various layered structures
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Barbara Gil, Wieslaw J. Roth, Justyna Grzybek, Aleksandra Korzeniowska, Zbigniew Olejniczak, Milan Eliáš, Maksym Opanasenko, Jiři Čejka
      The properties and catalytic activity of zeolite MWW were investigated before and after water treatment at 160°C for 48h to evaluate its possible behavior and usefulness in biomass conversion. Four different forms of the MWW zeolite were studied along with a sample of commercial zeolite beta for comparison: MCM-22, MCM-49, MCM-56 and Ce/MCM-22. The treated MWW zeolites showed lesser impact of the exposure to water than the tested zeolite beta. X-ray powder diffraction indicated negligible structural degradation. 27Al NMR and FTIR showed reduction of the acid site concentration, while micropore volume decreased by up to 50% as determined by nitrogen sorption. All MWW samples showed high catalytic activity in the reaction of n-propanol with 3,4-dihydro-2H-pyran (DHP). Similar reactions between tert-butanol and DHP also showed better activity and relatively small effect of the water treatment for the MWW materials with the exception of the Ce/MCM-22. The latter and the reference zeolite beta showed about 3 times lower conversion. Ce/MCM-22 was the only sample showing no decrease in acid site concentration as the result of aging in hot water so its lower activity was surprising. We propose that larger size of Ce may be responsible for blocking or otherwise affecting accessibility of the active sites. The study shows that MWW zeolites may show higher activity than zeolite beta. Incorporation of Ce improves stability of acid centers and although overall performance diminishes it leaves room for improvement, possibly by expanding the interlayer structure.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Performance of MCM-22 zeolite for the catalytic fast-pyrolysis of
           acid-washed wheat straw
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Héctor Hernando, Javier Fermoso, Cristina Ochoa-Hernández, Maksym Opanasenko, Patricia Pizarro, Juan M. Coronado, Jiří Čejka, David P. Serrano
      MCM-22 zeolite samples, having different Si/Al ratios, have been studied for the fast-pyrolysis of acid-washed wheat straw at two catalytic pyrolysis temperatures aimed to the production of partially upgraded bio-oil. The best combination of bio-oil deoxygenation activity and energy yield is obtained when the catalytic bed was operated at 450°C using the MCM-22 sample with the lowest Al content (Si/Al=40). Interestingly, the increase in the reaction temperature results in a lower amount of coke deposited over the zeolite. On the other hand, reducing the zeolite Si/Al ratio had a negative effect as a higher concentration of acid sites promotes non-desired reactions: severe cracking of the bio-oil vapours, leading to the enhanced production of gaseous hydrocarbons, and coke formation. Coke produced over MCM-22 zeolite exhibits high oxygen content, whereas the bio-oil fraction presents a high concentration of oxygenated aromatics. These results denote the limited aromatization activity of MCM-22 zeolite for producing aromatic hydrocarbons, in particular when compared with ZSM-5, being of interest for the selective production of phenolic compounds by biomass catalytic pyrolysis.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Methanol conversion over ZSM-12, ZSM-22 and EU-1 zeolites: from DME to
           hydrocarbons production
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Enrico Catizzone, Zaira Cirelli, Alfredo Aloise, Paola Lanzafame, Massimo Migliori, Girolamo Giordano
      Conversion of methanol to dimethyl ether (DME) and hydrocarbons was investigatedover zeolites with several 1-dimensional channel systems: ZSM-12, ZSM-22 and EU-1. The effect of reaction temperature, contact time and Time-On-Stream towards methanol conversion and products selectivity was investigated. It was found that ZSM-22 zeolite exhibits the best performances during conversion of methanol to DME (temperature range 180–240°C) as consequence of the particular shape selectivity that inhibits coke formation and deactivation. On the contrary, when formation of hydrocarbons is desired (temperature up to 320°C), ZSM-12 shows the highest activity in terms of light olefin yield with the highest C3/C2 ratio. The low selectivity towards C2 formation can be associated to the absence of both di- and tri-methyl benzenes formed during the reaction because when these species were detected, a higher ethylene productivity was observed lowering the C3/C2 ratio on the reactor out-stream.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • IR Operando study of ethanol dehydration over MFI zeolite
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Shashikant A. Kadam, Mariya V. Shamzhy
      Zeolite-catalyzed dehydration of ethanol is an attractive economically feasible route for production of ethylene and butenes. The goal of this contribution is to monitor the intermediate species on the surface of “working” catalyst to rationalize the influence of the reaction conditions and zeolite characteristics on the dehydration pathways. With this respect the rates of diethyl ether (DEE) and ethylene formation in ethanol dehydration along with the quantification of the surface-intermediates (ethanol monomer and dimer) were simultaneously assessed under different reaction conditions in H-MFI zeolite. The reaction conditions (pressure, temperature, and ethanol conversion) control the population of surface intermediates and hence determine the dominant reaction mechanism. The results support the prevalence of dimer-assisted etherification at high ethanol pressures and enhanced contribution of ethoxide-mediated route with increasing the temperature. At high conversion, the DEE decomposition route producing ethylene was confirmed for H-MFI at 488K along with ethoxide-mediated pathway.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Catalysts for conversion of ethanol to butanol: Effect of acid-base and
           redox properties
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Stefano Cimino, Luciana Lisi, Stella Romanucci
      The effect of acid-base properties of three different supports (hydroxyapatite, γ-Al2O3 and MgO) and of the redox properties of dispersed Ru or Ni on the catalytic conversion of ethanol into butanol has been investigated. Catalytic tests have been carried out in the temperature range 200–500°C by feeding an ethanol/N2 mixture to a lab-scale fixed bed reactor of powdered catalyst. Both supports and metal containing materials were deeply characterized by XRD, N2 physisorption, CO2 and NH3 TPD, H2 TPR. Highest butanol yields were associated to low ratio between acid and basic centres, typical of MgO, and to the easy reducibility of well dispersed metals as well. Good butanol yields can be also ascribed to the enhancement of both surface area and basicity of MgO provided by metal addition.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Surfactant templated synthesis of porous VOx-ZrO2 catalysts for ethanol
           conversion to acetaldehyde
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Ishtvan Boldog, Pavel Čičmanec, Yadolah Ganjkhanlou, Roman Bulánek
      Synthesis of VOx-ZrO2 catalysts with hierarchical porosity is reported here for first time. Surface areas of prepared materials reached values up to 211m2/g with the intrinsic porosity on the border between micro- and mesopores. Physico-chemical properties and catalytic activity in ethanol oxidative dehydrogenation to acetaldehyde of these materials are compared with VOx/ZrO2 catalyst obtained by vanadia deposition on the surface of the already synthesized zirconia support with the hierarchical micro-meso-macroporosity with macrochannels of 200–500nm in size. The VOx/ZrO2 sample prepared by deposition of vanadium on hierarchical zirconia exhibits high catalytic activity (TOF=106.9h−1 at 200°C), and especially high selectivity towards acetaldehyde. Acetaldehyde selectivity under reaction conditions varied between 99 and 92%. Directly synthesized VOx-ZrO2 catalysts showed higher selectivity to acetaldehyde compared to VOx/ZrO2 catalyst obtained by vanadia deposition on the surface of the already synthesized zirconia, but significantly lower activity probably due to incorporation of vanadium during the synthesis inside the channel walls where vanadium is not accessible to the gas molecules.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Catalytic hydrodeoxygenation of m-cresol over Ni2P/hierarchical ZSM-5
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Antonio Berenguer, James A. Bennett, James Hunns, Inés Moreno, Juan M. Coronado, Adam F. Lee, Patricia Pizarro, Karen Wilson, David P. Serrano
      Bifunctional catalysts comprising Ni2P supported over a hierarchical ZSM-5 zeolite (h-ZSM-5) were synthesized and applied to the hydrodeoxygenation (HDO) of m-cresol, a model pyrolysis bio-oil compound. Surface and bulk characterization of Ni2P/h-ZSM-5 catalysts by XRD, TEM, DRIFTS, TPR, porosimetry and propylamine temperature-programmed desorption reveal that Ni2P incorporation modifies the zeolite textural properties through pore blockage of the mesopores by phosphide nanoparticles, but has negligible impact of the micropore network. Ni2P nanoparticles introduce new, strong Lewis acid sites, whose density is proportional to the Ni2P loading, accompanied by new Brönsted acid sites attributed to the presence of POH moieties. Ni2P/h-ZSM-5 is ultraselective (>97%) for m-cresol HDO to methylcyclohexane, significantly outperforming a reference Ni2P/SiO2 catalyst and highlighting the synergy between metal phosphide and solid acid support. m-Cresol conversion was proportional to Ni2P loading reaching 80 and 91% for 5 and 10wt% Ni respectively. Turnover frequencies for m-cresol HDO are a strong function of Ni2P dispersion, evidencing a structure sensitivity, with optimum activity observed for 4nm particles.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Zr-USY zeolite: Efficient catalyst for the transformation of xylose into
           bio-products
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Clara López-Aguado, Marta Paniagua, Jose Iglesias, Gabriel Morales, José L. García-Fierro, Juan A. Melero
      A series of bifunctional USY zeolite catalysts with different Al/Zr ratios were synthesised. The incorporation of Zr into the structure was accomplished after partial dealumination of H-USY. Structural and spectroscopic characterization confirmed the preservation of the zeolite network as well as the isolated incorporation of Zr atoms in Al vacancies, with no evidence of large zirconia domains. The catalytic evaluation in the transformation of xylose in 2-propanol allowed to obtain interesting mixtures of bio-products, and to identify the presence of two competitive routes: the formation of GVL following alternating acid-driven and hydrogen-transfer (MPV) steps, and the retro-aldol condensation of xylose. The extent of each of these two competing reaction cascades is strongly dependent on the Zr loading. Thus, the catalyst with the lowest Al/Zr ratio favours the xylose retro-aldol condensation. When considering furfural as starting substrate, only products involved in the cascade to GVL are obtained. In this case, the incorporation of Zr in the catalyst favoured the MPV reactions, enhancing furfural conversion rate. Thus, increasing concentrations of products coming from the reduction of furfural–furfuryl alcohol, furfuryl 2-propyl ether, lactones-, were detected over Zr-USY samples, with the Zr-USY-3 yielding 13.5% of the final product, GVL. The catalysts are reusable after thermal regeneration at 550°C.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Synthesis of hierarchical Beta zeolite with uniform mesopores: Effect on
           its catalytic activity for veratrole acylation
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): J.M. Escola, D.P. Serrano, R. Sanz, R.A. Garcia, A. Peral, I. Moreno, M. Linares
      Uniform mesoporosity has been effectively developed in hierarchical Beta zeolite by means of a hydrothermal treatment at 110°C with an ammonia/surfactant solution. As a result, the broad pore size distribution, existing within the supermicropore-mesopore range in the parent hierarchical Beta sample, was rearranged into a uniform one centred at 40Å. In contrast, this treatment was less effective when applied to a conventional Beta zeolite sample with little secondary porosity. Neither amorphous phases nor MCM-41-like materials were detected after the mesopore narrowing treatment. Likewise, FTIR/pyridine measurements of the zeolite samples indicated that their acid properties were preserved after the ammonia/surfactant treatment, while just small variations were observed in the Si/Al ratio. Veratrole acylation tests were employed for assessing the catalytic properties of the samples. In spite of the reduction in the BET surface area produced by the mesopore narrowing treatment, the samples with uniform mesopores exhibited enhanced catalytic activity. In particular, the highest veratrole conversion was attained with the h-Beta (mnt) sample, obtained from the hierarchical Beta material. This result denotes the benefits derived from the presence of a high quality uniform mesoporosity on the catalytic performance of hierarchical Beta zeolite, as it increases the accessibility to the active sites and decreases the zeolite deactivation by product inhibition.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Comparison of H+ and NH4+ forms of zeolites as acid catalysts for HMF
           etherification
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Paola Lanzafame, Katia Barbera, Georgia Papanikolaou, Siglinda Perathoner, Gabriele Centi, Massimo Migliori, Enrico Catizzone, Girolamo Giordano
      MOR, BEA, MFI (containing or not Al) zeolites in the ammonium and protonic forms are studied in the etherification of HMF (5-hydroxymethylfurfural) in anhydrous ethanol. The conversion of HMF to 5-(ethoxymethyl)furan-2-carbaldehyde (EMF), and ethyl 4-oxopentanoate (EOP) occurs through two parallel reactions, which may be good described kinetically by pseudo-first order rates of formation, being the ethanol the co-reactant and the reaction medium. FTIR data with pyridine and 2,4,6-collidine as probe molecules are used to quantify the amount of Lewis and Brønsted sites in the samples. In the MOR, BEA, MFI (containing or not Al) series of zeolites in acid and ammonium form, a good relationship between the rate constant in EMF formation (k1) and the amount of strong Lewis acid sites (LAS) is observed. A correlation between rate constant in EOP formation (k2) and the amount of Brønsted acid sites (BAS) is instead observed. While the first correlation is independent on the acid or ammonium form, the second correlation depends on this aspect.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Over– and low–exchanged Co/BEA catalysts: General characterization and
           catalytic behaviour in ethane ammoxidation
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Safaa Essid, Faouzi Ayari, Roman Bulánek, Jan Vaculík, Mourad Mhamdi, Gérard Delahay, Abdelhamid Ghorbel
      Ethane ammoxidation into acetonitrile was successfully catalyzed between 380 and 450°C over Co/BEA solids issued from solid–state ion exchange with different metal loads. During the preparation, in the presence of NH4 + –Beta zeolite (Si/Al=12.5), CoCl2 precursor decomposes under helium stream without evaporation, leading to the stabilization of bare Co2+ at the exchange cationic sites as revealed by spectroscopic tools. However, at 4.13 and 5.63 wt.% of Co (Co/Al molar ratio equal to 0.75 and 1, respectively), the corresponding solids stabilized, besides bare β–type Co2+ ions, Co oxo [Co(III)O]+ species, revealed by H2–TPR. These species exhibit highest catalytic activity on the basis of TOF calculation and play a key role in ethane ammoxidation into acetonitrile at low temperature (380°C). Nevertheless, the excess of cobalt is transformed into Co3O4 oxide (as revealed by XRD and TPR experiments) which catalyzes the hydrocarbons combustion into CO2.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Me-ZSM-5 monolith foams for the NH3-SCR of NO
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Nicola Gargiulo, Domenico Caputo, Giorgio Totarella, Luciana Lisi, Stefano Cimino
      Self-supported ZSM-5 zeolite monolith foams (ZMFs) with different Si/Al ratios have been successfully prepared by hydrothermal synthesis with a polyurethane foam (PUF) template followed by calcination in air at 550 °C to harden. Cu or Mn have been introduced on preformed ZMF samples to obtain monolithic catalysts that have been fully characterized by morphological (XRD and SEM), textural (BET and pore size distribution), mechanical (compressive strength) and chemical (ICP-MS) analyses, and eventually tested in the Selective Catalytic Reduction of NO with NH3 in the temperature range 100–450 °C. The zeolite monolith foams are characterized by a well crystallized ZSM-5 structure, a BET surface area ca. 420 m2 g−1 and remarkable mechanical resistance even without any binder. Those structured catalysts show specific catalytic activity in line with powdered counterparts, but they can guarantee improved NO conversion due to the higher amount of catalyst per unit volume of reactor and to their superior mass transfer coefficients coupled to low internal diffusion limitations.

      PubDate: 2018-02-05T10:37:13Z
       
  • Semi-crystalline Fe-BTC MOF material as an efficient support for enzyme
           immobilization
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Victoria Gascón, Mayra B. Jiménez, Rosa M. Blanco, Manuel Sanchez-Sanchez
      Metal-organic frameworks (MOFs) have revolutionized the potential applications of nanoporous materials. One of the most recent and promising applications of these materials is their use as supports for enzyme immobilization. In this context, the in-situ (one-step) methodologies, which do not require the use of MOFs with pores larger than the enzyme to be immobilized, seem to be particularly encouraging. This work presents a systematic study of the semi-crystalline Fe-BTC MOF material (commercialized as Basolite F300) employed as support of the enzymes laccase and lipase through either in-situ or post-synthesis methodology. The presence of the enzyme in the resultant solid biocatalysts was proved by CHNS chemical analysis, thermogravimetric analysis, Bradford assays and by SDS-PAGE electrophoresis. The enzymatic activity of the resultant Fe-BTC-based biocatalysts was also tested. The in-situ approach is particularly relevant due to various reasons: (i) the enzyme immobilization is given in one step; (ii) it is rapid (10min); (iii) it is very efficient in terms of encapsulation capacity (≥98% for laccase and ≥87% for lipase); (iv) the enzymes are fully retained and no leaching is observed after an initial release of only around 10% of the enzyme molecules weakly immobilized; and (v) the activity of the retained enzyme can be substantially maintained (97% with respect to the free enzyme in the case of lipase). Any of these parameters systematically improves these given by the post-synthesis (two-step) approach. Moreover, Fe-BTC widely surpasses the benefits given by other MOF-based supports either by in-situ or post-synthesis approaches.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Metathesis of cardanol over ammonium tagged Hoveyda-Grubbs type catalyst
           supported on SBA-15
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Hynek Balcar, Naděžda Žilková, Martin Kubů, Miroslav Polášek, Jiří Zedník
      Cardanol (a mixture of phenols with C15 aliphatic unsaturated chain in meta position, manufactured from cashew nut shell liquids) is an abundant and till now practically waste natural material. An important way leading to its utilization as a renewable source of valuable phenolic compounds is represented by olefin metathesis. Quaternary ammonium tagged Ru complex of Hoveyda-Grubbs type immobilized on SBA-15 mesoporous molecular sieve by non-covalent interactions was proved as a very efficient catalyst for cardanol metathesis under mild conditions (35°C, toluene, 0.1 mol% of catalyst). The catalyst was used also in cross-metathesis of cardanol with alkenes (1-hexene, 1-heptene, 3-hexene, 4-octene) and unsaturated esters (methyl acrylate, 1,4-diacetoxybutene-2) under high yields of cross-metathesis products. The catalysts exhibited low leaching (from 0.2ppm to 2.9ppm Ru in products) and can be used in a continuous flow reactor (cumulative TON=2500).
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      PubDate: 2018-02-05T10:37:13Z
       
  • Sustainable photo-assisted CO oxidation in H2-rich stream by simulated
           solar light response of Au nanoparticles supported on TiO2
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Elisa Moretti, Elena Rodríguez-Aguado, Antonia Infantes- Molina, Enrique Rodríguez-Castellón, Aldo Talon, Loretta Storaro
      In this study the photo-response behaviour of Au/TiO2 systems in the preferential CO oxidation in a H2-rich stream (CO-PROX) was investigated by the first time under simulated solar light irradiation at room temperature and atmospheric pressure. Au nanoparticles, with an average size of 2–5nm, were precipitated-deposited on a mesoporous TiO2, previously synthesized by sol-gel type procedure and thermally treated at different temperatures to obtain anatase/rutile mixed phases. Structural, chemical and optical properties were studied by means of AAS, N2 physisorption, XRD, HR-TEM, DRUV–vis and XPS, investigating the effects of TiO2 polymorphs (anatase, rutile and combination thereof). All samples, containing a very low amount of noble metal (0.5wt%), resulted very active in the photocatalytic CO-PROX at ambient conditions, attaining very high CO conversion and CO2 selectivity values. The Au/TiO2 sample containing both anatase/rutile polymorphs in the support displayed the highest activity, both in dark and under simulated solar light, due to the simultaneous presence of these two titania crystalline phases, capable to lower the effective band gap of the composite system (2.90eV) and improving the photocatalytic activity in the studied reaction. This kind of materials may provide a sustainable and feasible approach to selectively oxidize CO in H2-rich stream under solar light irradiation and ambient conditions.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Hydrogen production via aqueous-phase reforming of methanol over nickel
           modified Ce, Zr and La oxide supports
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Martina Stekrova, Aleksi Rinta-Paavola, Reetta Karinen
      Aqueous-phase reforming (APR) of methanol over nickel supported on zirconium, cerium and lanthanum oxides was performed in continuous laboratory scale reactor and discussed in this paper. The role of composition and physico-chemical properties of the supports were investigated and significant benefit of using mixed oxides CeO2-ZrO2 and La2O3-ZrO2 over the pure oxides, in term of methanol conversion and hydrogen production, was demonstrated. Methanol conversion of over 50% with hydrogen production efficiency of over 40% were achieved with the most active catalyst Ni/25%CeO2-ZrO2. Furthermore, catalyst stability, the most challenging issue within APR studies, was thoroughly investigated and discussed. Slight deactivation of the prepared catalysts during APR experiments or reduction was observed and addressed to the Ni particles sintering. On the other hand, other common reasons causing catalysts deactivation under APR conditions, such as leaching of Ni, changes in Ni oxidation state or changes in the supports lattice were not observed by wide range of characterization methods The most stable catalyst, Ni/10%La2O3-ZrO2, exhibited a slight decrease of MeOH conversion within two subsequent experiments (each per 6h) from 46.3% to 42.7%.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Valorization of alginate for the production of hydrogen via catalytic
           aqueous phase reforming
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Giuseppe Pipitone, Davide Tosches, Samir Bensaid, Alessandro Galia, Raffaele Pirone
      Alginate, a carbohydrate abundant in the outer cell wall of macroalgae, was subjected to catalytic aqueous phase reforming (APR) to produce hydrogen using a 3% Pt/C commercial catalyst. The performance of the process was evaluated according to the conversion of the carbon to gas, the hydrogen yield and the hydrogen selectivity. The catalyst and feed amount, temperature, reaction time, pH and the presence of H2 were modified to understand the dependence of the outcome of the process on these parameters. The presence of the catalyst was fundamental in order to increase the hydrogen yield compared to the uncatalyzed reaction, and it can be reused without activity loss. In addition, it was observed that the increase in alginate loading led to a decreasing conversion of the carbon; the yield of hydrogen increases with the increasing temperature and the basic pH had a strong beneficial effect in terms of selectivity. The plateau appeared after 2h was attributed to the low kinetic tendency of the intermediate compounds to produce hydrogen. The study validated what is present in literature for simpler molecules, moving at the same time towards a more complex feed, closer to a possible industrial application.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Aluminum wire meshes coated with Co-Mn-Al and Co oxides as catalysts for
           deep ethanol oxidation
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Květa Jirátová, František Kovanda, Jana Balabánová, Petra Kšírová
      Aluminum meshes with different wire diameter and open space area were anodized in H2SO4 solution and then treated under hydrothermal conditions in aqueous solution of Co and Mn nitrates; the layered double hydroxide precursors formed on the supports surface were transformed into Co-Mn-Al mixed oxides after heating. For comparison, aluminum mesh coated with Co3O4 oxide was also prepared. Properties of the supported catalysts were characterized by XRD, SEM, TPR, and Raman spectroscopy and examined in deep ethanol oxidation. It was found that activity of the catalysts depended on the amount of active components deposited on the supporting mesh. Comparison of specific activities (calculated as amount of ethanol converted per unit weight of active oxides) at the same space velocity demonstrated the size of mixed oxides particles as the important parameter for oxidation activity: decreasing in particle size led to increased catalysts efficiency. The Co3O4 oxide deposited from Co(OH)2 suspension provided more active catalyst than Co-Mn-Al mixed oxides obtained by long-term hydrothermal treatment of the anodized aluminum meshes followed by heating.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Gold nanoclusters prepared from an eighteenth century two-phases procedure
           supported on thiol-containing SBA-15 for liquid phase oxidation of
           cyclohexene with molecular oxygen
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): J. Agundez, L. Martin, A. Mayoral, J. Pérez-Pariente
      The present work describes the incorporation of finely divided and well-dispersed Au species into SBA-15 mesoporous silica functionalized with mercaptopropyl groups, and the catalytic activity of the resulting Au-materials in the liquid phase oxidation of cyclohexene with molecular oxygen at atmospheric pressure. The gold entities have been prepared through a two-phase system described in the eighteenth century involving a solution of gold in a mixture of nitric acid and ammonium chloride (aqua regia) and rosemary oil. Gold nanoclusters, which present a disordered structure and sizes below 3nm, and even single gold atoms which may be anchored/stabilized through sulphur groups are found immobilized on the mesoporous support, but no gold nanoparticles (with well-defined structure and usually over ∼5nm) are detected. Such observations have been carried out by Cs-corrected STEM-HAADF where the visualization of bright spots is attributable to these individual entities. These materials are active in the oxidation of cyclohexene, but their relative activity is governed by the synthesis conditions. Partial aggregation of the gold entities into nanoparticles has been observed during the reaction, which are mainly responsible for the catalytic activity. The allylic oxidation of the cyclohexene ring over the double bond epoxidation is strongly favored, and at high conversion the two dominants products are 2-cyclohexen-1-one and 2-cyclohexen-1-ol.

      PubDate: 2018-02-05T10:37:13Z
       
  • CO2 methanation over Ni catalysts based on ternary and quaternary mixed
           oxide: A comparison and analysis of the structure-activity relationships
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Chalachew Mebrahtu, Salvatore Abate, Siglinda Perathoner, Shiming Chen, Gabriele Centi
      Methanation of CO2 was studied in a high throughput reactor (Amtech SPIDER 16) over Ni catalysts supported on ternary and quaternary alumina-zirconia-titania-ceria mixed oxides, in order to compare them under industrial relevant conditions and derive indications about the structure-activity relationships and specifically the role of ceria. The samples were characterized by BET, XRD, H2-TPR, CO-chemisorption, XPS and CO-TPD analyses. Catalytic activity was evaluated towards CO2 methanation at 5bar pressure, temperature range of 300–400°C and different Gas Hourly Space Velocities (GHSVs). The results showed that enhanced catalytic activity depends on both textural improvements (for the ternary oxide supported Ni) and reducibility and metal dispersion (for the quaternary oxide supported Ni). The comparison between both groups of catalysts revealed that addition of CeO2 to 20%Ni/Al2O3-ZrO2-TiO2 further improves the catalytic performance. The catalyst supported on a mixed oxide support with 15wt% of ceria, titania and zirconia (the remaining 55% is alumina) exhibits the highest CO2 conversion (82%) and methane selectivity (98%) at 350°C and GHSV of 4000h−1. The role of CeO2 as promoter is to increase Ni dispersion and stabilize the presence of β-type NiO species which are reduced at lower temperatures. Other promoters (TiO2, ZrO2) have mainly a textural effect. Moreover, CeO2 promotes also the stability decreasing the deactivation rate of about one order of magnitude with respect to the best ternary system (Ni/C5) investigated.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Development of photoanodes for photoelectrocatalytic solar cells based on
           copper-based nanoparticles on titania thin films of vertically aligned
           nanotubes
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): F. Tavella, C. Ampelli, L. Frusteri, F. Frusteri, S. Perathoner, G. Centi
      Titania nanotube (TNT)-array thin films well decorated by copper nanoparticles with average size of 3nm were prepared by spray coating of a solution containing size-controlled Cu0 nanoparticles. The consecutive calcination at 300°C and 450°C leads to the oxidation of these Cu NPs to CuO, with small amounts of Cu2O at the lower calcination temperature, but maintaining the high dispersion. Analogous materials prepared by copper electrodeposition lead to significantly larger Cu NPs. The TNT-array thin film shows significantly enhanced photocurrent (up to about 90%) with respect to a comparable thin film prepared by spin coating using a commercial TiO2 P25 sample. The behavior is similar by applying different filters to cut part of solar light simulator radiation. Particularly, using an UV B/C blocking filter, which permits to pass light in the 350–550nm range, an about two-fold intensification in the current-to-electrical energy conversion (normalized to the same total irradiance) is obtained. The presence of CuO nanoparticles decreases the photocurrent density with respect to the support alone (TNT-array 1h), but enhances the H2 photogeneration rate in the gas-phase photoreactor experiments. The results indicate that in the tested experimental conditions, the main role of CuO nanoparticles is to act as co-catalyst to improve the H2 photogeneration rate rather than to promote charge separation or other effects, which promote the photocurrent density.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Photo-activated degradation of tartrazine by H2O2 as catalyzed by both
           bare and Fe-doped methyl-imogolite nanotubes
    • Abstract: Publication date: 15 April 2018
      Source:Catalysis Today, Volume 304
      Author(s): Elnaz Bahadori, Vincenzo Vaiano, Serena Esposito, Marco Armandi, Diana Sannino, Barbara Bonelli
      Imogolite-like nanomaterials were tested as heterogeneous catalysts for the photo-catalytic degradation of tartrazine (a food dye recalcitrant to biodegradation and responsible of allergic and/or intolerance reactions) in the presence of H2O2. Methyl-imogolite, a hybrid organic/inorganic material with chemical composition (OH)3Al2O3SiCH3, occurs as single-walled nanotubes with an inner surface lined by Si-CH3 groups and an aluminum oxo-hydroxide outer surface, where octahedral Al3+ ions may be isomorphically substituted by Fe3+ ions. Besides bare methyl-imogolite, novel Fe doped nanotubes (with nominal composition (OH)3Al2-xFexO3SiCH3, where x=0.025 or 0.050) were prepared by ion exchange of preformed methyl-imogolite with FeCl3 ×6H2O in water. Physico-chemical characterization of the materials showed that Fe doping positively modifies nanotubes light absorption capacity by lowering the band gap of methyl-imogolite from 4.9eV to 2.4eV. At higher Fe content (sample with nominal composition (OH)3Al1.950Fe0.050O3SiCH3), some Fe oxo-hydroxide clusters form, due to the natural tendency of Fe to form aggregates. Photo-degradation tests of tartrazine show that both bare and Fe-doped methyl-imogolite efficiently remove the dye from aqueous mixtures through different mechanisms. With bare methyl-imogolite, under UV light almost 65% Total Organic Carbon (TOC) is removed within 2h, likely due to the formation of reactive AlOOH groups promptly generating HO radicals. With sample having nominal composition (OH)3Al1.975Fe0.025O3SiCH3, Fe3+ species undergo efficient photo-Fenton reaction under UV light, leading to 90% TOC removal after 2h. Conversely, the Fe oxo-hydroxide clusters at nanotubes outer surface likely worsen the photo-Fenton activity of the sample with (OH)3Al1.950Fe0.050O3SiCH3 nominal composition as far as the TOC removal is concerned.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Effects of support materials and silver loading on catalytic ammonia
           combustion properties
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Satoshi Hinokuma, Hiroki Shimanoe, Yusuke Kawabata, Shun Matsuki, Saaya Kiritoshi, Masato Machida
      In this research, the effects of support materials and silver (Ag) loading on catalytic NH3 combustion properties were studied. Among the Ag supported on various metal-oxide materials, Ag/Al2O3 exhibited high catalytic NH3 combustion activity and high N2 (lowN2O·NO) selectivity. The combustion activity is closely associated with the Ag dispersion which is estimated using the O2–H2 titration technique. Thus, highly dispersed Ag nanoparticles on supports play a crucial role in the low-temperature light-off of NH3, implying that the support materials significantly affect the Ag dispersion. Although Ag/Al2O3 with higher amounts of Ag loading tended to exhibit higher combustion activity, the optimum Ag loading was found to be approximately 10wt.%. At the optimum Ag loading concentration, Ag/Al2O3 performed well during the catalytic NH3 combustion reaction. The local structures of the catalysts were investigated via transmission electron microscopy, X-ray absorption fine structure and gas adsorption techniques. After an NH3 combustion reaction at a temperature of 900°C, Ag/Al2O3 slightly deactivated because of the sintering of metallic Ag nanoparticles and the decreased surface area.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Catalytic performance of supported Ir catalysts for NO reduction with C3H6
           and CO in slight lean conditions
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Yasuyuki Doi, Masaaki Haneda
      Supported Ir catalysts effectively catalyzed the NO reduction with CO and C3H6 under slight lean and high-temperature conditions, although supported Pt and Pd showed the activity for NO reduction in low temperature region with narrow window. The NO reduction activity of supported Ir catalysts was quite different depending on the support oxide. Among them, Ir/SiO2 and Ir/CeO2 were the highest and lowest active catalysts, respectively. Although no relationship between the reducibility estimated by H2-TPR and the NO reduction activity was observed, TPO measurements revealed that the stability of Ir species in catalytically active reducing state is a key factor to determine the NO reduction activity. In situ FT-IR spectroscopy confirmed the formation of catalytically active reduced Ir species during the reaction. From the comparison of the wavenumber of IR band due to adsorbed CO species with the NO reduction activity, too strong Ir – support interaction causes the formation of stable Ir oxide species, resulting in the depression of NO reduction activity. The role of support oxide for Ir catalyst was concluded to stabilize the Ir species in catalytically active reducing state created during the reaction via the Ir – support interaction.
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      PubDate: 2018-02-05T10:37:13Z
       
  • A thermogravimetric study of CoTiO3 as oxygen carrier for chemical looping
           combustion
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Jong Ha Hwang, Eun Nam Son, Roosse Lee, Soo Hyun Kim, Jeom In Baek, Ho Jung Ryu, Ki Tae Lee, Jung Min Sohn
      CoTiO3 perovskite was investigated as an alternative oxygen carrier for chemical looping combustion. The cyclical reduction and oxidation reaction were performed in TGA equipment. When the CoTiO3 particles were reduced, oxygen transfer capacity was maintained at 10.2 wt% during 10th cycles with 15% H2/N2 and 10.5 wt% with 15% CH4/N2. It was similar to the theoretical oxygen transfer capacity, 10.3 wt%. The maximum oxygen transfer rate was 0.015 mmol O2/g/sec during the reduction process. For 15% CH4/N2, the transfer rate was 0.03 mmol O2/g/sec which was twice that resulting from using hydrogen. From XRD and TPR results, CoTiO3 was transformed to Co/TiO2 and CoCx during reduction with hydrogen and methane, respectively. After all cycles, the particles were not agglomerated and appeared to be similar to its initial state. Conclusively, CoTiO3 could be a potential candidate as an oxygen carrier because CoTiO3 shows an improved oxygen transfer capacity and rate.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Effect of pore structure of TiO2 on the SO2 poisoning over V2O5/TiO2
           catalysts for selective catalytic reduction of NOx with NH3
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Seunghee Youn, Inhak Song, Hwangho Lee, Sung June Cho, Do Heui Kim
      We applied 5wt%V2O5/TiO2 catalysts supported on two types of TiO2 having distinctive pore structure, mesopore (DT-51) and micropore (microporous TiO2; micro) to selective catalytic reduction of NOx with NH3 (NH3 SCR) to investigate the effect of pore structure of TiO2 on sulfur poisoning. During the SCR reaction in the presence SO2 for 12h, 5wt% VT (DT-51) showed more drastic decrease in activity than 5wt% VT (micro). Larger amount of SO2 was desorbed over the post-reaction 5wt% VT (DT-51) sample during the temperature programmed decomposition which was consistent with the elemental analysis. Such larger amount of sulfate formation could be explained by the more active SO2 oxidation on the 5wt% VT (DT-51) than 5wt% VT (micro) because SO2 oxidation is the key step to generate sulfate species on the catalysts. It could be ascribed to the difference in the tendency of oxidation reaction affected by the vanadium species, since it was known that more VOV bonds existed on the surface of 5wt% VT (DT-51) having bulk-like VOx species whereas VO bonds were prevalent on 5wt% VT (micro) having more dispersed VOx. In situ FT-IR results also provided the evidence about the formation of ammonium bisulfate through strong interaction between NH3 and SO3 on 5wt% VT (DT-51), although 5wt% VT (micro) did not. It can be summarized that the different vanadium species determined by the pore structure of TiO2 have a significant effect on the sulfur poisoning during SCR reaction.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Synthesis of Pt/mesoporous SiC-15 and its catalytic performance for
           sulfuric acid decomposition
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Hassnain Abbas Khan, Prakash Natarajan, Kwang-Deog Jung
      Sulfuric acid (SA) decomposition is one of the key reactions in the sulfur-iodine (SI) cycle to produce hydrogen. Catalysts for the SA decomposition should be active and stable in a wide temperature range of 550–850°C to absorb latent heat generated from a thermal solar heat or a very high temperature nuclear reactor. Here, mesoporous mSiC-15 is prepared using the SBA-15 template. TEM analysis shows that the morphology of the mSiC-15 has the replica structure of SBA-15. Pt/SBA-15 and Pt/mSiC-15 catalysts are prepared by impregnation and the catalytic activity is examined under the reaction condition of 650–850°C and a GHSV of 76,000mL/gcat/h. The Pt/mSiC-15 catalyst is relatively stable for 50h at 850°C, while the Pt/SBA-15 was severely deactivated. The Pt amounts on the Pt/SBA-15 and Pt/mSiC-15 catalysts decreased from 0.73 and 0.80wt% at initial reaction time to 0.39 and 0.68wt% after 12h reaction, respectively. The Pt loss during the SA reaction is main cause of deactivation, which is caused by the evaporation of Pt oxides under O2 environment produced during the SA decomposition. It is observed that the Pt particles are embedded in porous SiO2 (Pt/mSiO2), which is transformed from Pt/mSiC-15 during the SA decomposition for 6h. The Pt/mSiC-15 was relatively active and stable for the SA decomposition and the Pt loss was minimized by the structural change from Pt/mSiC-15 to Pt/mSiO2 after 6h.
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      PubDate: 2018-02-05T10:37:13Z
       
  • Dynamic chemical state conversion of nickel species supported on silica
           under CO–NO reaction conditions
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Shohei Yamashita, Yusaku Yamamoto, Hisataka Kawabata, Yasuhiro Niwa, Misaki Katayama, Yasuhiro Inada
      The chemical state conversion of Ni species supported on SiO2 under CO and NO atmosphere was observed by in situ XAFS techniques, and the reversible and quantitative chemical state conversions between NiO and Ni(0) were clarified during the temperature-programmed reduction of NiO by CO and the temperature-programmed oxidation of Ni(0) by NO. The evaluated chemical state of the SiO2-supported Ni species indicated the catalytic CO–NO reaction conditions using the Ni/SiO2 catalyst. The actual catalytic experiments demonstrated the achievement of the catalyzed CO–NO reaction at 873K. The dynamic chemical state analysis by means of the time-resolved dispersive XAFS method revealed the existence of a transient Ni species, which was partially oxidized by the faster reaction with NO. The formed NiO species can oxidize the CO molecule, and thus the CO–NO reaction is driven by the redox conversion of the supported Ni species.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Enhanced three way catalytic activity of NiFe2O4 by physically mixed metal
           oxides
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Shiori Nagai, Kakuya Ueda, Junya Ohyama, Atsushi Satsuma
      The NOx reduction activity of NiFe2O4 in automotive three-way catalysis was enhanced by physical mixing with CeO2, MgO, ZrO2, and Al2O3, while the mixing with TiO2 and Nb2O5 did not promoted the catalytic activity. On both pure NiFe2O4 and the physically mixed catalysts, NO was mainly reduced by C3H6 under the NO-C3H6-CO-O2 reaction conditions, because the temperature dependence of NO conversion in NO-C3H6-CO-O2 reaction was the same as that in NO-C3H6-O2 reaction. The in-situ FT/IR measurement revealed that the NO reduction proceeded with (1) partial oxidation of C3H6 to surface carboxylates, i.e., acetate and formate as good reductants for NO, and (2) reduction of NO by surface carboxylates. The metal oxide additives did not have catalytic activity for partial oxidation of C3H6 nor for NO oxidation to NO2, except CeO2. The main promotion effect was attributed to storage and release of surface carboxylates by metal oxide additives.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Catalytic activity of AlF3 nano-structure for hydrolysis of NF3
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): No-Kuk Park, Yong Han Jeong, Jin Wook Lee, Tae Jin Lee
      This study examined the catalytic properties of AlF3 nanostructures for the hydrolysis of NF3 discharged from semiconductor processes. Alumina being used as a catalyst for the hydrolysis of NF3 was converted to AlF3 by fluorination in the presence of NF3 during a gas-solid chemical reaction. In general, AlF3 has low catalytic activity in the hydrolysis of fluorinated compounds, but its catalytic activity varies according to its crystal structure. Commercial AlF3 exhibited low catalytic activity in the hydrolysis of NF3, whereas AlF3 formed from the chemical reaction between NF3 and alumina exhibited very high catalytic activity. Although alumina has high catalytic activity in the hydrolysis of NF3, its activity decreases as it is converted to AlF3 during the process. On the other hand, the activity test and X-ray diffraction showed that its catalytic activity is recovered as the nanocrystals of AlF3 were grown. AlF3 nanocrystals grown by the gas-solid chemical reaction showed a similar distribution of acid sites as the alumina. These acid sites provided the catalytic activity of AlF3 in the hydrolysis of NF3.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Spectroscopic study on multicyclic and long-time stability of CO2
           adsorbent in flue gas conditions
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Jhulimar M. Celedonio, Rose Mardie Pacia, Young Soo Ko
      Since the development of amine-functionalized adsorbent is critical for its large-scale implementation, an investigation on the stability in realistic process condition is significantly important. The amine-functionalized CO2 adsorbents were prepared via impregnation of primary amine (1NS-P/SiO2), secondary amine (1NS-S/SiO2) and diamines (2NS/SiO2) into a silica support. The degradation products that could have caused the deactivation of the adsorbents are determined and quantified by in-situ FT-IR measurement and deconvoluted FT-IR spectra. The adsorbents were evaluated for their stability in multiple temperature swing adsorption (TSA) cycles and long-time CO2 or air exposure at elevated temperature. It revealed that the degradation of adsorbents and its rate depended on the amine structure and gas conditions and that two main degradation species were urea and amide. Primary amine was more prone to CO2-induced degradation than secondary amine. Secondary amine was less stable than primary amine for O2-induced degradation. Diamine showed both CO2- and O2-induced degradations. To assess which has a more detrimental effect on the stability of the adsorbents between CO2 and O2 gases, the effect of long-time exposure of the adsorbents in pure CO2 or air was determined at 150°C using both TG and in-situ FT-IR measurement. The long-time exposure of 1NS-P/SiO2 to CO2 caused about 50% loss in CO2 uptake with the faster accumulation of linear urea. The long-time exposure to air caused just about 13% loss in CO2 uptake with the slower accumulation of amide. 1NS-S/SiO2 showed better stability for CO2 than 1NS-P/SiO2 without any decrease in capacity and without any changes in its spectra. 2NS/SiO2 showed that urea formed faster than amide. It was degraded more in air than in CO2 with about 92% and 51% loss of CO2 uptake, respectively. It can be inferred from the results that O2-induced degradation is more detrimental than CO2-induced degradation.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Acidic and catalytic properties of ZSM-5 zeolites with different Al
           distributions
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Sungsik Park, Turgren Biligetu, Yong Wang, Toshiki Nishitoba, Junko N. Kondo, Toshiyuki Yokoi
      The impact of the organic species in the synthetic gel of ZSM-5 on the distribution of Al atoms in the MFI framework and catalytic performance was investigated; ZSM-5 zeolites were synthesized by exclusively using TPAOH, and Na cations with PET to elucidate how the distribution of Al atoms is governed by the types of organic species in the synthetic gel. The distribution of Al atoms was investigated by 27Al MAS NMR technique and constrain index (CI). Catalytic cracking of 1-octene over the ZSM-5 catalysts was carried out to estimate “hydrogen transfer coefficient (HTC) and cracking mechanism ratio (CMR) values”. We found that HTC and CMR values are dependent on the distribution of Al atoms. The fine-control of Al distribution in the MFI structure could improve the tolerance for coke deposition in 1-octene cracking.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Synthesis of high-energy-density fuel over mesoporous aluminosilicate
           catalysts
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Jongjin Kim, Beomseok Shim, Gayoung Lee, Jeongsik Han, Ji Man Kim, Jong-Ki Jeon
      This study focused on the effect of the incorporation of aluminum on the catalytic performance of KIT-6 in the norbornadiene cyclodimerization reaction. An Al-KIT-6 material synthesized through Al grafting over siliceous KIT-6 was shown to have a well-ordered mesoporous structure and a large pore size. The grafting of Al onto siliceous KIT-6 generated weak acid sites consisting of Lewis acid sites and Brönsted acid sites. Cyclodimerization of norbornadiene was carried over Al-KIT-6 catalysts in a batch reactor in order to compare their activity with that of the Al-MCM-41 catalyst. The activity of norbornadiene cyclodimerization over the Al-KIT-6 catalyst was higher than that over the Al-MCM-41 catalyst, which could be attributed to the larger pore diameters of the Al-KIT-6 catalyst. The acidity and the catalytic activity of the Al-KIT-6 catalyst as used here could easily be recovered through filtering and calcination in an air atmosphere at 550°C.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Direct synthesis of liquefied petroleum gas from syngas over H-ZSM-5
           enwrapped Pd-based zeolite capsule catalyst
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Peipei Zhang, Guohui Yang, Li Tan, Peipei Ai, Ruiqin Yang, Noritatsu Tsubaki
      A facile synthesis route, named dual-layer crystal growth method, was developed for preparing Pd-based zeolite capsule catalyst. The millimeter-sized zeolite capsule catalyst (Pd/SiO2-SZ) with a core-shell structure was prepared by a developed dual-layer crystal growth method: coating Silicalite-1 and H-ZSM-5 zeolite orderly as double shells encapsulating the Pd/SiO2 core catalyst. We employed the prepared Pd/SiO2-SZ zeolite capsule catalyst for the direct synthesis of liquefied petroleum gas (LPG) from syngas (CO+H2). In the reaction, the zeolite capsule catalyst showed excellent LPG selectivity than the single core catalyst of Pd/SiO2 and the physical mixture catalyst prepared by a simply mixing core and shell catalysts. The Pd/SiO2-SZ realized the highest LPG selectivity of 34.4% with CO conversion of 14.1%. Moreover, the optimal reaction temperature and pressure in the reaction for LPG direct synthesis from syngas over Pd/SiO2-SZ catalyst were 623K and 5.0MPa, respectively. The high performance of zeolite capsule catalyst Pd/SiO2-SZ was attributed to the enforced mass transfer diffusion from inside to outside of the catalyst.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Selective and stable production of ethylene from propylene over
           surface-modified ZSM-5 zeolites
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Jong-Won Jun, Tae-Wan Kim, Seok Il Hong, Joo-Wan Kim, Sung Hwa Jhung, Chul-Ung Kim
      This study is the first to examine the selective production of ethylene from propylene (propylene-to-ethylene, PTE) with using various structural types of zeolites. The catalytic performances of these zeolite catalysts were tested in a continuous fixed-bed reactor system with respect to ethylene selectivity and catalyst stability during the overall reaction period. Among these zeolite catalysts, ten-membered ring zeolites with three-dimensional pore structures (ZSM-5 and ZSM-11) exhibited stable catalytic performances with considerable ethylene selectivity compared to other zeolite catalysts. The ZSM-5 zeolite, thus selected, was further studied in the PTE reaction with different silica-alumina ratios (Si/Al2, SARs), a surface modification with phosphorus, and under different reaction conditions in order to investigate the effect of acidity, surface properties, and process variables on the catalytic activity as well as to additional improve the ethylene selectivity. From these studies, the PTE reaction was found to depend strongly on the reaction condition, SAR and surface P modification in the ZSM-5 zeolite. The phosphorous-modified ZSM-5 catalyst exhibited the highest ethylene selectivity of more than 70% with moderate propylene conversion of 36.3% at a low propylene space velocity and a low partial pressure condition.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Selective ethanol synthesis via multi-step reactions from syngas:
           Ferrierite-based catalysts and fluidized-bed reactor application
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Hyungwon Ham, Jihyeon Kim, Jong Hun Lim, Woo Chang Sung, Dong Hyun Lee, Jong Wook Bae
      Selective ethanol synthesis from syngas through cascade multi-step reactions via methyl acetate (MA) intermediate route was investigated using a highly crystalline ferrierite (FER) zeolite and hybridized bifunctional Cu-ZnO-Al2O3/FER (CZA/FER). The extent of crystallinity of the FER zeolites played crucial roles for catalytic activities of syngas conversion to dimethyl ether (DME), DME carbonylation to MA and MA hydrogenation to ethanol. With an increase of crystallinity of FER, DME productivity by CO2 (or CO) hydrogenation was largely enhanced due to a fast dehydration rate of methanol to DME on the CZA/FER having a large surface area of metallic copper nanoparticles. The bifunctional CZA/FER was utilized to convert MA to ethanol up to the similar equilibrium yield of ∼42 mol%. In addition, highly crystalline of FER@FER, which was synthesized by using a FER seed, showed a higher DME conversion to MA and stability due to the abundant presence of Bronsted acid sites with less defect sites. To verify the possible integration of two series cascade reactions such as direct syngas conversion to DME and its consecutive carbonylation to MA, the segregated double-layer formation in one bubbling fluidized-bed reactor was simulated. Two catalytic reaction regions with a light and dense-phase at similar reaction conditions were completely segregated at optimal linear velocity ranges (minimum fluidizing velocity, Umf) by using two different catalyst particle sizes having an average size of 112.5 and 82.5μm in a bottom and upper reaction zone, respectively.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Effect of acidity on Ni catalysts supported on P-modified Al2O3 for dry
           reforming of methane
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Seonu Bang, Eunpyo Hong, Sung Woo Baek, Chae-Ho Shin
      Phosphorus-modified Al2O3 supports containing different P content were prepared to control the acidity of Ni-impregnated catalysts for application in the dry reforming of methane (DRM). Results from the H2-temperature-programmed reduction showed that an increase in P content promoted the formation of an AlPO4 phase, and resulted in an increase in Ni particle size. Although the initial conversion of CH4 and CO2 decreased with increasing P content, the addition of P influenced on the acidic properties of the support and the catalyst. Indeed, a decrease in catalytic deactivation correlated with the decreasing acidity of the P-modified supports and the Ni/P-Al2O3 catalysts, and the acidic properties were determined by the behaviors of the temperature-programmed desorption of iso-propanol (IPA) and the dehydration of IPA. We found that the Ni/Al2O3 catalyst modified by 2wt.% P exhibited the weakest acidity whilst demonstrating excellent coke resistance and stability over 100h in the DRM reaction.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Hydrogenolysis of glycerol with in-situ produced H2 by aqueous-phase
           reforming of glycerol using Pt-modified Ir-ReOx/SiO2 catalyst
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Shiyang Liu, Masazumi Tamura, Zheng Shen, Yalei Zhang, Yoshinao Nakagawa, Keiichi Tomishige
      We found that Pt-modified Ir-ReOx/SiO2 acted as an effective catalyst for aqueous phase reforming (APR) and selective C-O hydrogenolysis of glycerol without external hydrogen sources at low temperature of 463K, and that 0.5wt% loaded Ir-ReOx/SiO2 (Pt(0.5)-Ir-ReOx/SiO2) provided 1,2-propanediol (1,2-PrD) and acetol in high total yield of 53% at 81% conversion. The initial activity (TOFinitial) over Pt(0.5)-Ir-ReOx/SiO2 at 463K was estimated to be 13h−1. Pt-Ir alloy and Ir-ReOx species in Pt-Ir-ReOx/SiO2 are main active species for APR and selective C-O hydrogenolysis, respectively, and the high yield can be achieved by balancing the APR and hydrogenolysis activities through the optimization of Pt and Ir-ReOx molar ratio.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Synthesis of Lower Olefins from Synthesis Gas over Active Carbon-Supported
           Iron Catalyst
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Kenji Asami, Kazuki Komiyama, Kohei Yoshida, Hiroki Miyahara
      Synthesis of C2-C6 lower olefins from synthesis gas was investigated through Fischer-Tropsch synthesis (FTS) reaction over active carbon-supported iron catalyst with a small amount of Cu (Fe-Cu/AC) catalysts using a fixed bed reactor at 300°C at 2.1MPa. Mn promoted catalyst (Fe-Cu-Mn/AC) gave high yield and selectivity to the lower olefins. Added Mn species seemed likely to locate uniformly on the AC surface to form complex oxide with iron oxide. A high yield of ca. 40% is obtainable at high H2/CO ratio of 4. The catalyst showed stable activity and selectivity for 100h. CO2 addition in the feed gas enhances the yield further by suppressing the water gas shift reaction.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Catalytic cracking of soybean oil by ZSM-5 zeolite-containing
           silica-aluminas with three layered micro-meso-meso-structure
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Atsushi Ishihara, Takashi Tsukamoto, Tadanori Hashimoto, Hiroyuki Nasu
      In order to convert a large molecule of soybean oil, ZSM-5 zeolite-containing silica-aluminas with three layered micro-meso-meso-structure were developed. In this method, zeolite-containing two layered silica-aluminas initially prepared were combined with silicas having very large mesopores prepared by the gel skeletal reinforcement. The three-layered structure was confirmed by pore size distribution derived from N2 adsorption and desorption measurements. The catalytic cracking of soybean oil using the three-layered catalysts was evaluated by the Curie point pyrolyzer method. When the reaction was performed at 500°C, activities of catalysts having hierarchical structures were improved. It is thought that the diffusion of soybean oil molecule was promoted in the presence of large mesopores of the catalysts having hierarchical structure. ZSM-5 zeolite-containing catalysts showed very high research octane number (RON), compared with β zeolite and Y zeolite containing catalysts, indicating that ZSM zeolite-containing catalysts provided gasoline fractions of good quality. Gasoline yields increased with increasing conversion and was plotted on the same straight line when the same type of zeolite was used, indicating that the product selectivity would depend on the type of zeolite and that the activity would strongly depend on the existence of the matrix.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Two-step continuous upgrading of sawdust pyrolysis oil to deoxygenated
           hydrocarbons using hydrotreating and hydrodeoxygenating catalysts
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Gayoung Kim, Jangwoo Seo, Jae-Wook Choi, Jungho Jae, Jeong-Myeong Ha, Dong Jin Suh, Kwan-Young Lee, Jong-Ki Jeon, Jae-Kon Kim
      The two-step hydrodeoxygenation of pine sawdust pyrolysis oil, or bio-oil, is performed using pairs of first-step hydrotreating and second-step hydrodeoxygenating catalysts. The reaction results demonstrate that the combination of hydrotreating carbon-supported 5wt% Pd (5wt% Pd/C) and hydrodeoxygenating tungstate-zirconia-supported 3wt% Ru (3wt% Ru/WZr) catalysts produced the highest yield of oil products and the lowest yield of cokes and tars. The hydrodeoxygenated liquid products are further analyzed using FT-IR, which indicates the removal of carbonyls and hydroxyls along with an increase of methyls. The roles of hydrotreating Pd/C are further studied using GC/MS results of the hydrotreated liquid products; these results indicate that the hydrogenation of carbonyls to alcohols and the saturation of furans occur during the first step of the hydrotreating process. The removal of carbonyls and unsaturated furans can suppress their strong adsorption to noble metal surfaces and then their carbonization to cokes.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • Effect of catalytic reactor bed dilution on product distribution for
           Fischer-Tropsch synthesis over Ru/Co/Al2O3 catalyst
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Gi Hoon Hong, Young Su Noh, Ji In Park, Seol A Shin, Dong Ju Moon
      The effect of catalytic reactor bed dilution on product distribution in Fischer-Tropsch synthesis (FTS) over Ru/Co/Al2O3 catalysts was investigated. Ru/Co/Al2O3 catalysts were prepared by a two-step impregnation method and characterized by N2 physisorption, CO chemisorption, XRD, and TPR techniques. The catalyst bed was prepared by the layered dilution method with four different cases. The dilution of the catalyst bed affected the temperature profile and bed residence time of the catalytic reactor bed. Furthermore, CO conversion and CH4 selectivity were affected by temperature distribution, which varied with the degree of dilution in the fixed-bed reactor. The olefin to paraffin ratio of C2-C4 products and the chain growth probability (α) were influenced by the residence time of the catalytic reactor bed, which varied with the layered dilution method. A transition zone was thought to exist between the catalyst layers, which was referred to as an interval. With a long interval, the heat generated by the exothermic reaction over the catalyst layer would not be appropriately transferred from one layer to another, and the readsorption of α-olefin from pellet to pellet would also become more difficult. The dilution of the catalyst layer in the fixed-bed reactor was determined as an important parameter for optimizing product selectivity in the FTS reaction. Based on the results, the pellet to pellet readsorption model of α-olefin was proposed.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • High utilization of methanol in toluene methylation using MFI zeolite
           nanosponge catalyst
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Changq Lee, Seungjun Lee, Wookdong Kim, Ryong Ryoo
      A highly mesoporous MFI zeolite nanosponge, which was composed of a disordered assembly of 2.5-nm thick zeolite frameworks, was synthesized using a meso- and micropore dual structure-directing surfactant. The zeolite nanosponge was investigated as a catalyst for toluene methylation by methanol. The results showed remarkably high toluene conversion and xylene yield, in comparison with the bulk zeolite counterparts. The high catalytic performance was attributed to the suppression of side reactions that could convert methanol to linear hydrocarbons. This suppression can be attributed to the fact that the dealkylation of polymethylbenzenes, which must take place before linear hydrocarbon formation, did not occur significantly in the zeolite nanosponge as compared to the case of bulk zeolites. In addition to the aforementioned high performance, the MFI zeolite nanosponge was also superior to the bulk MFI in terms of catalytic longevity.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
  • On methanol to hydrocarbons reactions in a hierarchically structured ZSM-5
           zeolite catalyst
    • Abstract: Publication date: 1 April 2018
      Source:Catalysis Today, Volume 303
      Author(s): Heejoong Kim, Hoi-Gu Jang, Eunhee Jang, Sung Jun Park, Taehee Lee, Yanghwan Jeong, Hionsuck Baik, Sung June Cho, Jungkyu Choi
      Two type ZSM-5 catalysts (Si/Al ratio of ∼30) with different mesoporosity were synthesized by using a structure directing agent of tetra-n-butylphosphonium hydroxide. In particular, the molar compositions of ethanol and water in the synthetic precursor were changed in order to acquire the two type ZSM-5 catalysts. The resulting ZSM-5 catalysts were formed via the interconnection of very thin pillars or lamellae; (1) ∼6nm thick with marked mesoporosity (H_30; high mesoporous ZSM-5) and (2) ∼13nm thick without any considerable mesoporosity (L_30; low mesoporous ZSM-5). The pyridine-based acid titration reveals that H_30 had internal Brønsted acid sites similar to those in the commercially available ZSM-5 with a Si/Al ratio of 75 (referred to as C_75), though H_30 contained a large amount of external Brønsted acid sites. The methanol to hydrocarbons (MTH) reaction performance of these two ZSM-5 catalysts demonstrates that H_30 preferred to produce propene over ethene compared to C_75, while L_30 showed a very poor MTH performance mainly due to the lower amount of internal Brønsted acid sites. More desirably, a very short diffusional length (∼18,600 times lower than that in C_75) in H_30 considerably disfavored the aromatic dealkylation that is known to produce ethene. With this, H_30 allowed for achieving the ratio of propene to ethene as high as ∼9.1, which is, to the best of our knowledge, a highest value among the MTH results on ZSM-5 catalysts without any co-feed. Furthermore, ceria-doped H_30 not only enhanced the stability for the MTH reaction via a passivation of the external Brønsted acid sites, but also improved a propene to ethene ratio up to ∼15.0.
      Graphical abstract image

      PubDate: 2018-02-05T10:37:13Z
       
 
 
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