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ENGINEERING (1201 journals)                  1 2 3 4 5 6 7 | Last

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Journal Cover Catalysis Today
  [SJR: 1.348]   [H-I: 164]   [5 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0920-5861
   Published by Elsevier Homepage  [3041 journals]
  • IFC - Editors; Editorial Board & scope
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286


      PubDate: 2017-03-20T13:51:00Z
       
  • Contents list
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286


      PubDate: 2017-03-20T13:51:00Z
       
  • Progress in the Electrochemical Synthesis of Ammonia
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): V. Kyriakou, I. Garagounis, E. Vasileiou, A. Vourros, M. Stoukides
      Ammonia is one of the most important and widely produced chemicals worldwide with a key role in the growth of human population. Nowadays, the main route for ammonia synthesis is the Haber-Bosch process, developed a century ago. In this process, Fe-based catalysts are usually employed at temperatures between 400 and 500°C and pressures between 130 and 170bar. As opposed to the industrial process, in nature, plants and bacteria have been producing ammonia for millions of years at mild conditions. Atmospheric nitrogen is reduced by solvated protons on the FeMo cofactor of the metalloenzyme nitrogenase. The natural method of nitrogen fixation has motivated several research groups to explore the electrochemical synthesis of ammonia at ambient pressure. Since it was first demonstrated in 1998, the electrochemical synthesis has been studied in a variety of experimental configurations over a wide temperature range (25–800°C). In the present review, the progress of this method in both solid and liquid electrolyte cells is reported. The experimental studies are divided into high (T>500°C), intermediate (500°C>T>100°C) and low (T<100°C) temperatures. The experimental observations are comparatively discussed with theoretical predictions based on DFT calculations. The techno-economic advantages and disadvantages of the electrochemical approach, as well as the requirements to be met in order to enable practical applications are also analyzed.
      Graphical abstract image

      PubDate: 2017-03-20T13:51:00Z
       
  • Role of alkali promoter in ammonia synthesis over ruthenium
           catalysts—Effect on reaction mechanism
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Ken-ichi Aika
      Previous research on ammonia synthesis over ruthenium catalysts is reviewed with a particular emphasis on the action of alkali promoters. The concept of electron donation and the nature of the adsorbed species are examined, and their relationship with electronic and structural factors related to dinitrogen activation is considered. A kinetic analysis is performed and the reaction mechanism involved in ammonia synthesis over ruthenium catalysts is investigated.
      Graphical abstract image

      PubDate: 2017-03-20T13:51:00Z
       
  • Coordination chemistry insights into the role of alkali metal promoters in
           dinitrogen reduction
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Gannon P. Connor, Patrick L. Holland
      The Haber-Bosch process is a major contributor to fixed nitrogen that supports the world's nutritional needs and is one of the largest-scale industrial processes known. It has also served as a testing ground for chemists' understanding of surface chemistry. Thus, it is significant that the most thoroughly developed catalysts for N2 reduction use potassium as an electronic promoter. In this review, we discuss the literature on alkali metal cations as promoters for N2 reduction, in the context of the growing knowledge about cooperative interactions between N2, transition metals, and alkali metals in coordination compounds. Because the structures and properties are easier to characterize in these compounds, they give useful information on alkali metal interactions with N2. Here, we review a variety of interactions, with emphasis on recent work on iron complexes by the authors. Finally, we draw conclusions about the nature of these interactions and areas for future research.
      Graphical abstract image

      PubDate: 2017-03-20T13:51:00Z
       
  • Electrocatalytic ammonia synthesis via a proton conducting oxide cell with
           BaCe0.5Zr0.3Y0.16Zn0.04O3-δ electrolyte membrane
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): S. Klinsrisuk, J.T.S. Irvine
      Ceramic membrane cells of BaCe0.5Zr0.3Y0.16Zn0.04O3-δ (BCZYZ) have been developed for electrocatalytic ammonia synthesis. Unlike the high-pressure Haber-Bosch process, an atmospheric synthesis of ammonia was attempted in this work. The membrane cells were fabricated by tape casting and the electrode materials were applied by ion impregnation. The impregnated electrodes comprised NiO/CeO2 composite anode and iron oxide cathode. The formation of ammonia was studied in the range of 400–500°C. The addition of Pd catalyst into the iron oxide cathode enhanced the ammonia formation rate while the addition of Ru improved only the electrochemical performance. The highest ammonia formation rate of 4×10−9 mols−1 cm−2 was obtained from Pd-modified cell at 450°C. The current efficiency of ammonia formation was in the range of 1–2.5% while that of H2 evolution varied from 0 to 60% depending on applied potentials. The total current efficiency close to 100% was obtained from Pd-modified cell.
      Graphical abstract image

      PubDate: 2017-03-20T13:51:00Z
       
  • Electrochemical synthesis of ammonia from wet nitrogen via a dual-chamber
           reactor using La0.6Sr0.4Co0.2Fe0.8O3−δ-Ce0.8Gd0.18Ca0.02O2−δ
           composite cathode
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Ibrahim A. Amar, Rong Lan, John Humphreys, Shanwen Tao
      A La0.6Sr0.4Co0.2Fe0.8O3−δ-Ce0.8Gd0.18Ca0.02O2−δ composite cathode was used to investigate the electrochemical synthesis of ammonia from wet nitrogen. Wet nitrogen was flown through a dual chamber reactor under atmospheric pressure leading to the successful synthesis of ammonia. Ammonia was synthesised at a rate of 1.5×10−10 mols−1 cm−2 at 400°C when applying a dc voltage of 1.4V, which is the highest reported to date. This rate is twice that of the observed ammonia formation rate (7×10−11 mols−1 cm−2) when Co-free cathode, La0.6Sr0.4FeO3−δ-Ce0.8Gd0.18Ca0.02O2−δ was used as the cathode catalyst. A higher catalytic activity for ammonia synthesis may be obtained when using a catalyst with high oxygen vacancies, with the introduction of oxygen vacancies at the cathode being a good strategy to improve the catalytic activity of ammonia synthesis.
      Graphical abstract image

      PubDate: 2017-03-20T13:51:00Z
       
  • Recent progress towards the electrosynthesis of ammonia from sustainable
           resources
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Michael A. Shipman, Mark D. Symes
      Ammonia (NH3) is a key commodity chemical of vital importance for fertilisers. It is made on an industrial scale via the Haber Bosch process, which requires significant infrastructure to be in place such that ammonia is generally made in large, centralized facilities. If ammonia could be produced under less demanding conditions, then there would be the potential for smaller devices to be used to generate ammonia in a decentralized manner for local consumption. Electrochemistry has been proposed as an enabling technology for this purpose as it is relatively simple to scale electrolytic devices to meet almost any level of demand. Moreover, it is possible to envisage electrosynthetic cells where water could be oxidised to produce protons and electrons at the anode which could then be used to reduce and protonate nitrogen to give ammonia at the cathode. If this nitrogen were sourced from the air, then the only required infrastructure for this process would be supplies of water, air and electricity, the latter of which could be provided by renewables. Hence an electrosynthetic cell for ammonia production could allow NH3 to be generated sustainably in small, low-cost devices requiring only minimal facilities. In this review, we describe recent progress towards such electrosynthetic ammonia production devices, summarizing also some of the seminal literature in the field. Comparison is made between the various different approaches that have been taken, and the key remaining challenges in the electrosynthesis of ammonia are highlighted.
      Graphical abstract image

      PubDate: 2017-03-20T13:51:00Z
       
  • Onset potentials for different reaction mechanisms of nitrogen activation
           to ammonia on transition metal nitride electro-catalysts
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Younes Abghoui, Egill Skúlason
      Recent theoretical calculations with DFT suggest that transition metal nitrides (TMNs) are promising materials to catalyze N2 electroreduction to ammonia at ambient conditions. To realize which mechanism is more favourable, we conduct DFT calculations to explore the catalytic activity of these materials in their most stable structures via conventional associative (AM) and dissociative (DM) mechanisms, and then compare the corresponding results with that of Mars-van Krevelen (MvK) mechanism we recently reported. The dissociation of N2 on the clean surfaces is endothermic on most of these nitrides and the activation barriers large in all cases, which is inhibitive of a DM on these materials. The onset potential predicted for ammonia formation on these TMNs is always less negative via MvK than with AM, except a few cases, where both mechanisms have similar onset potentials. In those cases, the AM is less favourable than MvK since the adsorption of N2 molecule is endothermic. Therefore, the MvK is almost always the favourable mechanism. We used the computational hydrogen electrode method and neglected any proton-electron transfer reaction barriers in this work but including those will be necessary to make a more definitive statement, which is the subject of future work.
      Graphical abstract image

      PubDate: 2017-03-20T13:51:00Z
       
  • Electrochemical synthesis of ammonia via Mars-van Krevelen mechanism on
           the (111) facets of group III–VII transition metal mononitrides
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Younes Abghoui, Egill Skúlason
      Density functional theory (DFT) calculations were carried out on a new class of materials in pursuit of nitrogen activation and electrochemical ammonia formation at ambient conditions. The source of proton provided by the anode could be either water splitting or H2. But we focused only on the cathode reaction here where nitrogen is reduced to ammonia. The Mars-van Krevelen mechanism was studied on the (111) facets of the NaCl-type structure of earlier transition metal mononitrides of Sc, Ti, V, Cr, Mn, Y, Zr, Nb, Mo, Hf, Ta, W, and Re. The catalytic activity was investigated, free energy of all intermediates was calculated along the reaction path and free energy diagrams were constructed to explore the potential-determining steps of the reaction and accordingly estimate onset potential necessary for nitrogen activation on each different metal nitrides. The possibility of catalyst poisoning in electrochemical environment was also scrutinized at the bias needed for running the reaction. In addition, hydrogen production on all these nitride candidates was explicitly considered within our mechanistic model by removing the constraint of proton adsorption occurring only on surface nitrogen atoms and accordingly most of these candidates show capability for suppressing competitive hydrogen production, in contrast to metallic surfaces that almost exclusively evolve hydrogen gas. The likelihood of catalyst decomposition and catalyst regeneration was assessed for the most interesting nitrides. It was found that the only active and stable nitride catalyst that can regenerate itself and activate nitrogen to ammonia is NbN, and others should decompose to their parental metals under operational conditions.
      Graphical abstract image

      PubDate: 2017-03-20T13:51:00Z
       
  • The inhibitor role of NH3 on its synthesis process at low temperature,
           over Ru catalytic nanoparticles
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Charles Leterme, Camila Fernández, Pierre Eloy, Eric M. Gaigneaux, Patricio Ruiz
      Single catalysts containing 3, 5 and 7wt.% of Ru (Ru3/Al2O3, Ru5/Al2O3 and Ru7/Al2O3) were prepared via impregnation of alumina with RuO2 colloidal suspensions. Two mechanical mixtures, containing Ru3/Al2O3 +Ru5/Al2O3 and Ru3/Al2O3 +Ru7/Al2O3, were also prepared. Catalytic activity was measured during low-temperature ammonia synthesis reaction. Three different tests were performed after reduction pretreatment of the catalysts: 1) Standard test, the catalytic activity of ammonia synthesis; 2) Test under NH3 +He treatment, following ammonia decomposition; 3) Test under NH3 +He+H2 treatment, following ammonia decomposition in presence of hydrogen. Standard tests were additionally used to study the effect of the different treatments (NH3 +He and NH3 +He+H2) on the catalytic activity of ammonia synthesis. Catalysts were characterized by N2 physisorption, XRD and XPS spectroscopy. The size of Ru nanoparticles influences their performance during ammonia synthesis. The important role of the average size and size distribution of Ru nanoparticles in their activity for ammonia synthesis has been confirmed. Catalysts having a broad size distribution of Ru nanoparticles are more active than those having a narrow size distribution of Ru nanoparticles. Ammonia treatment has a negative effect in ammonia synthesis: results suggest that NHx intermediates remaining strongly adsorbed on the surface inhibit the activity of catalysts during ammonia synthesis. The presence of hydrogen during NH3 treatment inhibits ammonia decomposition and induces weaker adsorption of NHx intermediates. The presence of large particles is necessary to reach and maintain a high catalytic activity during ammonia synthesis. Taking into account previous studies, it could be suggested that large Ru nanoparticles activates mobile hydrogen atoms that migrate towards small Ru nanoparticles, promoting NHx hydrogenation. When mixing two catalysts having different mean Ru sizes, there is a significant synergistic effect in the catalytic activity, due to a more effective hydrogenation of NHx intermediates.
      Graphical abstract image

      PubDate: 2017-03-20T13:51:00Z
       
  • Activity of iron pyrite towards low-temperature ammonia production
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Israel Temprano, Tao Liu, Stephen J. Jenkins
      In this work we report the characteristics of iron pyrite toward the production of ammonia at low temperatures under ultra-high vacuum conditions. We review (with additional unpublished details) our previous systematic study of nitrogen and hydrogen adsorption on single-crystal iron pyrite (FeS2) and summarise our earlier findings regarding the possibility of ammonia synthesis on this material. We also present new results concerning the adsorption of nitrogen and hydrogen on two related materials, namely molybdenum-treated iron pyrite surfaces and iron pyrite nanostructures deposited on a gold single-crystal. On the bare iron pyrite samples, ammonia is produced upon hydrogenation of preadsorbed N species at 230K, demonstrating that all hydrogenation steps are possible at low pressures and temperatures. Nitrogen adsorbs molecularly on FeS2{100} at low temperatures, desorbing at 130K, but does not adsorb dissociatively even at pressures up to 1bar. Adsorbed nitrogen species can, however, be obtained through exposure to excited nitrogen species. Hydrogen adsorbs on FeS2{100}, but only in the presence of an incandescent Ta filament. Recombinative desorption of H2 occurs at 225K and is accompanied by desorption of H2S at 260K. On the molybdenum-treated iron-pyrite, no appreciable Nads species were detected under the experimental conditions studied, and the same is true for iron pyrite nanostructures on Au{111}. We also provide further details of our efficient and reproducible method for preparing well-ordered stoichiometrically pure FeS2{100} suitable for surface science studies.
      Graphical abstract image

      PubDate: 2017-03-20T13:51:00Z
       
  • Wustite based iron-cobalt catalyst for ammonia synthesis
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Łukasz Czekajło, Zofia Lendzion-Bieluń
      By way of melting, iron and iron-cobalt wustite based catalysts promoted with oxides of calcium, aluminium, and potassium were obtained. Measurements of the activity in the ammonia synthesis reaction at pressure of 10MPa were conducted. A positive effect of cobalt addition into the wustite structure of the iron catalyst on increasing in the catalyst catalytic activity in the ammonia synthesis reaction, lowering a temperature, at which catalysts achieved the maximum reduction rate, decreasing values of the apparent activation energy of obtained catalysts, and increasing resistance to the overheating process was observed. All the results were compared with the results obtained for the industrial magnetite-based iron catalyst.
      Graphical abstract image

      PubDate: 2017-03-20T13:51:00Z
       
  • A method of determining nanoparticle size distribution in iron ammonia
           
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Rafał Pelka
      A new method for determination of nanoparticle size distribution, on the basis of measurements of nanomaterial conversion degree as a function of the chemical potential of gas reagent, was presented. The method was applied for determination of nanocrystallite size distribution in a pre-reduced iron catalyst for ammonia synthesis being an example of a nanomaterial. Samples were reduced with hydrogen at 500°C and then nitrided at 300°C in gaseous ammonia-hydrogen mixtures of different nitriding potentials. Conversion degree measurements, viz., measurements of mass changes of the catalyst were performed in a differential reactor equipped with systems that enable thermogravimetric measurements and analysis of gas phase chemical composition. Based on the performed measurements, a relationship binding the conversion degree with size distribution was proposed. The resulting size distribution of nanocrystallites was compared to distributions determined by known techniques based on XRD or on measurements of the nitriding reaction rate. The size distribution determined using the new method has a higher resolution, revealing more details of the sample morphology.
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      PubDate: 2017-03-20T13:51:00Z
       
  • Computational screening of perovskite redox materials for solar
           thermochemical ammonia synthesis from N2 and H2O
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Ronald Michalsky, Aldo Steinfeld
      To circumvent the scaling relations of activation energies and adsorption energies at catalytic surfaces limiting their catalytic activity, perovskites are investigated for a solar-driven production of ammonia (NH3) from N2 and H2O via a two-step redox cycle. The cycle consists of an endothermal reduction of N2 at 1400°C using solar process heat, followed by an exothermal hydrolysis forming NH3 at 400°C. Both steps are carried out at ambient pressure. Electronic structure computations are employed to assess the stability and surface activity of oxygen vacancies and lattice nitrogen at the (001) facet of nitrogen-doped perovskites. The results are compared to the activities of Mo2N(100), Mo2N(111), and Mn2N(0001) reference models. We find producing oxygen vacancies at high temperature that are active in N2 reduction is the energetically limiting reaction step of the redox cycle. The redox energetics can be tuned by the perovskite composition and are most sensitive to the type of transition metal at the B site terminating the surface. Promising perovskites contain Co or Mn at the surface and Co doped with Mo or W in the bulk, such as CaCoO3-terminated La0.5Ca0.5Mo0.5Co0.5O3, SrCoO3-terminated Sr0.5La0.5Co0.5W0.5O3, and CaMnO3-terminated Sr0.5Ca0.5MnO3. Trade-offs in the redox energetics are quantified to guide future experimental work.
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      PubDate: 2017-03-20T13:51:00Z
       
  • Ammonia decomposition over cobalt/carbon catalysts—Effect of carbon
           support and electron donating promoter on activity
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Laura Torrente-Murciano, Alf K. Hill, Tamsin E. Bell
      This paper sets the new design parameters for the development of low temperature ammonia decomposition catalysts based on readily available cobalt as an alternative to scarce but highly active ruthenium-based catalysts. By using a variety of carbon materials as catalytic supports, we systematically demonstrate that microporous supports capable of stabilising small cobalt crystallites (∼2nm) lead to high catalytic activities compared to bigger nanoparticles. Additionally, the degree of graphitisation of the carbon support has a detrimental effect on the activity of the cobalt (0) active sites, likely due to their potential as an electron donator. Consequently, the addition of electron donating promoters such as cesium substantially decreases the activity of the cobalt catalysts. This relationship deviates from the trends observed for ruthenium-based catalysts with an optimum 3–5nm size where an increase of the graphitisation degree of the support and the addition of electron donating promoters increases the ammonia decomposition activity.
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      PubDate: 2017-03-20T13:51:00Z
       
  • Influence of alkali metal amides on the catalytic activity of manganese
           nitride for ammonia decomposition
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Fei Chang, Jianping Guo, Guotao Wu, Peikun Wang, Pei Yu, Ping Chen
      Strong promoting effect of alkali metal amides, i.e., LiNH2, NaNH2 and KNH2, on the catalytic activity of manganese nitride (MnN) for ammonia decomposition has been demonstrated, which is evidenced by ca. 100K drop in onset temperature and by ca. 50–60kJmol−1 reduction in apparent activation energy as compared with the neat MnN. The order of promotion capability of alkali metal amides can be ranked as LiNH2 >KNH2 ≥NaNH2, either in term of NH3 conversion rate or turnover frequency (TOF), which is distinctly different from that of conventional alkali metal oxides or hydroxides, i.e., K>Na>Li. This phenomenon suggests that the promoting mechanism of alkalis depends on their chemical forms. When alkalis are in the form of amide or imide, they may function as co-catalysts by participating in the catalytic circle directly rather than by executing electronic promotion influence on transition metals.
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      PubDate: 2017-03-20T13:51:00Z
       
  • Nitrogen transfer properties in tantalum nitride based materials
    • Abstract: Publication date: 15 May 2017
      Source:Catalysis Today, Volume 286
      Author(s): Said Laassiri, Constantinos D. Zeinalipour-Yazdi, C. Richard A. Catlow, Justin S.J. Hargreaves
      Ta3-xMxNy (M=Re, Fe, Co; x=0, 0.25, 0.5, 1) materials with different microstructural features (e.g. surface area) were successfully prepared using different synthesis techniques. The dependence of nitrogen transfer properties upon tantalum nitride microstructure and its chemical composition was evaluated using the ammonia synthesis with a H2/Ar feedstream (a reaction involving lattice nitrogen transfer). It was shown that nitrogen reactivity for tantalum nitride is more dominated by lattice nitrogen stability rather than microstructural properties. In the case of non-doped tantalum nitride, only a limited improvement of reactivity with enhanced surface area was observed which demonstrates the limited impact of microstructure upon reactivity. However, the nature of the transition metal dopant as well as its content was observed to play a key role in the nitrogen transfer properties of tantalum nitride and to impact strongly upon its reactivity. In fact, doping tantalum nitride with low levels of Co resulted in enhanced reactivity at lower temperature.
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      PubDate: 2017-03-20T13:51:00Z
       
  • IFC - Editors; Editorial Board &amp; scope
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285


      PubDate: 2017-03-15T13:47:27Z
       
  • Contents list
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285


      PubDate: 2017-03-15T13:47:27Z
       
  • Women in catalysis
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): M. Olga Guerrero-Pérez


      PubDate: 2017-03-15T13:47:27Z
       
  • Electrocatalysts for low temperature fuel cells
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): M.V. Martínez-Huerta, M.J. Lázaro
      Low temperature fuel cells technologies are currently shifting very fast from fundamental research to real growth. The development of electrocatalysts plays a vital role in the electrocatalytic reactions involved in these devices, because the catalyst determines the overall reaction efficiency, durability and cost. This article review progress in the research and development of electrocatalysts for low temperature fuel cells technologies, with especial attention in the contribution of our research teams over the last 15 years or so. The intensive research efforts in reducing or replacing Pt-based electrodes in fuel cells have been focus in the use of carbon nanomaterials as electrocatalytic supports, including carbon nanostructures tailored by surface modification or building in particular dopants/defects. Recent research effort has also led to the use of electronic conductivity noncarbon support materials. In addition, carbon-composite materials are proving to be a robust, inexpensive and active electrocatalysts, where the synergetic effect between the carbon nanomaterials and the ceramic or polymer nanostructures can lead to a superior electrocatalytic performance and durability for low temperature fuel cells. Perspectives on these catalysts and possible pathways to address current remaining challenges are also discussed.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Environmental applications of titania-graphene photocatalysts
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Marisol Faraldos, Ana Bahamonde
      Nowadays, graphene is considered one important achievement as a consequence of its high potential in nanotechnologyand in the development of new environmental and energy processes. Reciently, graphene is receiving great attention in the area of photocatalysis, where is emerging in the next generation of photocatalysts, as a tool for enhancing photocatalytic performance and solar photoefficiency. Titanium dioxide hybridization with graphene has an effect on band gap energy decrease, shifting its absorption threshold to the visible light region and allowing to harness solar energy. So, the conjugation of graphene with semiconductor solid particles such as TiO2, results in photocatalysts with improved charge separation, reduced recombination of the photogenerated electron-hole pairs, increased specific surface area, and introduces an adequate quantity and quality of adsorption sites, given that enhances their electronic, optoelectronic, electrocatalytic and photocatalytic properties. This critical review sumarizes the recent progress in the design and synthesis of graphene-based titania semiconductor photocatalysts. Moreover, their applications in wastewater treatments, disinfection and air pollution control have been also discussed. Finally, some perspectives and challenges considered essential to extend the photoefficiency of these new photocatalysts in the visible region, to harvest directly solar light, have been suggested to introduce and elucidate new improvements in environmental photocatalytic processes.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Environmental uses of zeolites in Ethiopia
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Isabel Díaz
      In the past six years we have been intensively collaborating with the Chemistry Department of Addis Ababa University as well as Haramaya University to bust scientific knowledge related to zeolites and zeolite applications. Initially, we teamed up with geologists and government actors in the mining sectors; as a result we got access to natural zeolites from the north of the country, as well as other industrial minerals such as kaolin. In parallel we developed research activities in the use of zeolites as adsorbents and in catalytic processes related to environmental applications of necessity in Ethiopia. In the first part of this paper I will describe two examples of adsorption processes using mineral resources: one is a natural stilbite used to develop an adsorbent to remove fluoride from drinking waters; and the second one uses virgin kaolin to prepare a synthetic zeolite 4A that we used to remove chromium from tannery wastewaters. Finally, two catalytic examples will be described: in the first one we tackled the photocatalytic degradation of dyes from textile industries using Ti-modified natural and synthetic zeolites, and in the second one we used modified mordenites, both natural and synthetic, for the conversion of glucose into 5-HMF.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Asymmetric organocatalytic journey into the world of three-membered rings
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Sara Meninno, Alessandra Lattanzi
      in this review the development of new organocatalytic methodologies for the asymmetric synthesis of small heterocycles, namely epoxides, cyclopropanes and aziridines will be illustrated. This topic covers our research, carried out in the last eleven years, using bifunctional organocatalysts derived from the chiral pool. The authors will highlight the challenges as well as the evolution on the catalyst structure necessary to overcome the limits of reactivity and stereocontrol, encountered during the research. This “catalytic evolution” has been always observed in catalysis and it can be easily traced back to what has been happening in the fascinating and rapidly evolving area of asymmetric organocatalysis.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Sustainable vanadium-catalyzed oxidation of organic substrates with H2O2
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Barbara Floris, Federica Sabuzi, Alessia Coletti, Valeria Conte
      Metal catalyzed reactions are a powerful tool to design new chemical synthetic processes according to Green Chemistry principles, such as pollution prevention, atom economy, catalysis and the use of safer solvents and chemicals. The selection of the metal is particularly important to plan relevant and applicable processes: in particular, Vanadium is a good choice because it is cheap, naturally abundant and relatively non-toxic. Moreover, its rich redox chemistry makes it a suitable catalyst for a number of different reactions. A survey of catalytic vanadium-catalyzed oxidations investigated by our group in the last ten years is presented. Changing the ligand and the reaction conditions, the selective oxidation of model alkenes and sulfides and the oxidative bromination of alkenes, alkynes and toluene were successfully obtained. The introduction of substituent groups on the ligand scaffold allowed to investigate the ligand effect on the metal core by various techniques. These vanadium based catalytic systems found applications in the desulfurization of model fuel, the design of screen-printed electrodes for monitoring the hydrogen peroxide consumption and in sustainable synthesis.
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      PubDate: 2017-03-15T13:47:27Z
       
  • On the water structure at hydrophobic interfaces and the roles of water on
           transition-metal catalyzed reactions: A short review
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Xiaohong Zhang, Torrie E. Sewell, Brittany Glatz, Sapna Sarupria, Rachel B. Getman
      Interest into the roles of water on aqueous phase heterogeneous catalysis is burgeoning. This short review summarizes the influences of hydrogen bonding on adsorption and how water molecules act as co-catalysts in aqueous phase heterogeneous catalysis. These phenomena, which involve interactions and/or reactions with “dangling” hydroxyl or hydroxide groups from nearby water molecules, are related to interfacial phenomena that have been observed at water/oil interfaces in organic synthesis. The hypothesized water structures at water/oil interfaces in organic synthesis is presented, and predictions about how analogous structural effects could influence catalytic chemistry at water/transition metal interfaces are discussed. The focus of this review is on computational methods and observations, but some experimental methods and findings are discussed as well.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Silica-based nanocatalysts in the CC and C-heteroatom bond forming cascade
           
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): E. Pérez Mayoral, E. Soriano, V. Calvino-Casilda, M.L. Rojas-Cervantes, R.M. Martín-Aranda
      The design and development of hybrid materials with application in catalysis science is an interesting researching field, especially in the chemical industry for fine chemicals production. The properties of nanostructured catalysts can be changed by tuning the interaction between the support and the active phases. Silica nanoparticles are very convenient solid supports for the synthesis of organic-inorganic hybrid nanocatalysts, endowing them of the required features to optimize activity and selectivity, stability and recyclability. In this review, we analyze the latest developments and give a perspective concerning the recent applications of silica-based nanocatalysts for the synthesis of heterocyclic scaffolds, biologically active, via cascade reactions. Heterocyclic rings often are the structural cores responsible of the biological activities in natural products and synthetic compounds. These systems are frequently synthesized by multicomponent reactions (MCRs), through cascade reactions. Such versatile catalytic systems have been successfully applied in a great variety of organic transformations for the synthesis of complex molecules and would play a key role in establishing new and more efficient sustainable technologies.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Microemulsion droplets to catalytically active nanoparticles. How the
           application of colloidal tools in catalysis aims to well designed and
           efficient catalysts
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Magali Boutonnet, Margarita Sanchez-Dominguez
      In this review, we report the successful application of a colloidal tool, namely microemulsions (ME) in the design of catalysts for various applications. First, a brief introduction to MEs and the water-in-oil (w/o) ME reaction method is given. The first ME formulations used for catalyst synthesis are discussed. Catalytic activity of the materials obtained from those initial studies, both as particles deposited onto a support as well as directly as nanoparticles in ME suspension is described. Then various application examples which highlight several important properties of the catalysts obtained from w/o ME are given. For example, particle size control achieved with ME is very relevant to surface sensitive reactions, whose selectivity depends greatly on metal particle size. Another important aspect is related to the unique microenvironment of MEs which results in specific interactions within the formed materials; this is particularly important for certain catalysts such as mixed oxide particles, conferring them with special properties and enhanced performance. Comparison of activity and selectivity of impregnation-prepared versus ME-prepared materials is given for several catalytic reactions. Finally, the more recently developed oil-in-water (o/w) ME method is described, along with examples of materials obtained by this method as catalysts, including photocatalysis. The different aspects discussed in this review demonstrate the importance of the ME reaction method for the design of nanocatalysts with enhanced activity and selectivity.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Screening the bulk properties and reducibility of Fe-doped Mn2O3 from
           first principles calculations
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Elena Bazhenova, Karoliina Honkala
      Manganese oxides, particularly Mn2O3, have demonstrated great potential for oxygen carrier materials in chemical looping applications. The application of these materials in the industrial scale is hindered by thermodynamic restrictions related to the reoxidation process. This disadvantage can be overcome by doping the oxide with a guest cation. Iron is one of the most promising dopants, but the atomic-level understanding of its effects on the properties of α-Mn2O3 is incomplete. Herein, we report a systematic GGA+U study of the bulk properties and reducibility of FexMn2-xO3 (0≤x≤2) as a function of Fe dopant concentration. In particular, we focus on a representative set of 20 models with different Fe content, generated by screening several thousand structures. Our results indicate that substitution of Mn atoms with Fe stabilizes FexMn2-xO3, which is visible through negative values of doping energies, decreasing oxide formation energies, and higher oxygen vacancy formation energies with increasing Fe concentration. Similar to Fe, the presence of an oxygen vacancy increases the band gap in the major spin channel of FexMn2-xO3. Oxygen transport in FexMn2-xO3 is found to depend on Fe content and distribution in the lattice. All in all, our findings provide atomic-level insight into the properties of FexMn2-xO3 and generally agree with experimental observations. Obtained information can be applied to investigate the reactivity of FexMn2-xO3.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Structural and surface properties of heterogeneous catalysts: Nature of
           the oxide carrier and supported particle size effects
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Anna Maria Venezia, Valeria La Parola, Leonarda Francesca Liotta
      Heterogeneous catalysts, investigated by several techniques, such as XRD, XPS, TEM, TPR/TPO, able to ascertain their structural, chemical, electronic and morphology properties are reviewed with respect to selected results obtained by the group during approximately the last twenty five years. The field of application covers different catalytic processes such as alkene hydrogenation over noble metal catalysts, hydrodesulfurization (HDS) and environmental catalysis. In particular the following subjects are described: the peculiarity of a support like pumice, in relation to the hydrogenation activity of the supported noble metals; supported gold and supported gold containing alloy catalysts for different types of reactions; the importance of the CoMoS precursors and the structure of bimetallic PdAu and PtAu for hydrotreating processes; the effect of a sulfatable oxide, such as TiO2, on the CH4 oxidation activity of supported Pd catalysts; different preparation methods influencing significantly the catalytic behavior of supported nickel catalysts for methane conversion processes. The reviewing of the different case studies illustrates the importance of the interaction between support and active metals ultimately determining the surface distribution of the active sites and their final catalytic activity.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Hydrodeoxygenation of model compounds on sulfided CoMo/γ-Al2O3 and
           NiMo/γ-Al2O3 catalysts; Role of sulfur-containing groups in reaction
           networks
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Andrea Gutierrez, Eeva-Maija Turpeinen, Tuula-Riitta Viljava, Outi Krause
      Hydrodeoxygenation reactions were studied with model compounds on sulfided hydrotreating CoMo/γ-Al2O3 and NiMo/γ-Al2O3 catalysts with and without adding a sulfur-containing compound into the reaction mixtures. Clear differences were observed in the behaviour of the model compounds. The addition of H2S improved the reactivity of methyl heptanoate and guaiacol with the formation of methanethiol but decreased that of phenol. The presence of sulfur compounds in the gas phase affected also the selectivities reducing the hydrogenation activity of the catalysts and shifting the C7/C6 hydrocarbon distribution from methyl heptanoate. Thus sulfur groups present on the catalyst surface form the key components for the reactions. The reaction network of methyl heptanoate can be described with two types of reactions: reactions with only hydrogen addition and reactions with the contribution of the surface SH− groups. We propose that the ability of the nucleophilic SH− groups to interact with model compounds is a primary factor influencing the initial overall reactivity of the starting compounds. Furthermore, the increasing amount of SH− groups directed the distribution of hydrocarbons towards C6 instead of C7 hydrocarbons from methyl heptanoate by accelerating the decarbonylation/decarboxylation reaction and the 1-hexanethiol formation.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Catalysis in microstructured reactors: Short review on small-scale syngas
           production and further conversion into methanol, DME and Fischer-Tropsch
           products
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Hilde J. Venvik, Jia Yang
      Synthesis gas production and further conversion via the Fischer-Tropsch, methanol and dimethyl ether (DME) syntheses is currently economic only in the large scale. Compact, modular, and safe technology efficient in smaller scale would enable utilizing smaller natural gas fields, bio-syngas and even off-shore associated gas that otherwise would be flared or re-injected. So-called or microstructured reactors with superior heat and mass transfer properties and scalability by parallelization may offer opportunity for process intensification and different investment risk. Here, we summarize research into the performance of different combinations of catalyst properties and microchannel design. We find that intensified production of synthesis gas by steam reforming or catalytic partial oxidation remains associated with significant challenges to the reactor design, the catalysis and the materials. With respect to synthesis of methanol, DME or Fischer-Tropsch products, using a microchannel packed-bed with integrated heat exchange, the results are definitely more encouraging, enabling the use of highly active catalysts and severe process conditions without sacrificing on selectivity and stability.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Advances in methane conversion processes
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Bingwen Wang, Sandra Albarracín-Suazo, Yomaira Pagán-Torres, Eranda Nikolla
      In this short review, we highlight the recent advances in methane conversion processes at high and low temperatures. Methane conversion processes are of great importance in achieving a crude-oil independent supply of energy, fuels and chemicals for the future. Direct conversion of methane into chemicals and fuels has been often considered as the “holy grail” of current catalysis research due to the unreactive nature of methane, which makes targeted chemical transformations to fuels and chemicals very challenging. We discuss the progress in developing heterogeneous catalytic and electrocatalytic systems to overcome this challenge. We conclude by providing a perspective on the future of this area of research.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Ethylene production via Oxidative Dehydrogenation of Ethane using M1
           catalyst
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Anne M. Gaffney, Olivia M. Mason
      Ethylene is the top petrochemical produced worldwide with continuously growing production capacity. Steam Pyrolysis of straight run hydrocarbons is the conventional technology for producing ethylene for more than 50 years. Currently the feedstock of choice domestically is ethane or liquefied petroleum gas (LPG). Oxidative Dehydrogenation of Ethane (C2-ODH) is an alternative catalytic technology for producing ethylene using a natural gas feedstock. North American olefin plants have switched from a heavy petroleum feedstock to a light ethane feedstock due to the shale revolution. The M1 catalyst, advanced by co-author, Dr. Anne M. Gaffney, selectively and exothermically transforms ethane to ethylene under mild conditions (300–400°C, 4–7atm). A comparison of the two technologies shows the energy and cost savings of C2-ODH along with the promising future for oxidative dehydrogenation technology.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Combined theoretical and spectroscopic mechanistic studies for improving
           activity and selectivity in heterogeneous catalysis
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Mercedes Boronat, Patricia Concepción
      By combining theoretical modelling, in situ spectroscopy and kinetic studies it is possible to understand, at the molecular level, the role that the different types of active centres co-existing on real heterogeneous catalysts play on each elementary step of the global reaction mechanism. The fundamental knowledge acquired by means of this multi-disciplinary approach in two selected reactions, the chemoselective hydrogenation of substituted nitroaromatics and the Sonogashira coupling between aryl halides and alkynes, is applied to direct the rational synthesis of more efficient industrial catalysts based on noble metal particles supported on metal oxides.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Modern ssNMR for heterogeneous catalysis
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Olga B. Lapina
      This review is devoted to modern applications of solid state NMR (ssNMR) to the structural studies of heterogeneous catalysts. Recent developments of ssNMR combining high magnetic fields up to 23.5T, high rotation frequencies up to 120kHz, and the new software of spectra acquisition and processing coupled with quantum chemistry calculations allow unravel the 3D structure of active sites of the sophisticated structures, such as heterogeneous catalysts. Moreover, this opens a possibility of investigation of low sensibility nuclei that are generally assigned as inappropriate for NMR. Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy (DNP-SENS) is another powerful technique extending NMR application for surface feature investigation. Combination of modern ssNMR (including DNP) and DFT calculations synthesize the most powerful approach (so called NMR crystallography) of structural research of catalysts which is demonstrated on several remarkable application examples on challenging nuclei.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Porous carbon: A versatile material for catalysis
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Inês Matos, Maria Bernardo, Isabel Fonseca
      Heterogeneous catalysis is an exciting field in constant development. New and improved catalysts that can both be effective and economical are always on demand. Activated carbons may well play an important role in this field, as they are a cheaper alternative while more environmentally benign. In this paper, a brief overview of the effort developed in the application of activated carbon as heterogeneous catalysts in various reactions is presented. Functionalised activated carbon has been used as catalyst for fine chemical reactions. Gas-phase reactions for NO, N2O and CO2 conversions were thoroughly studied using activated carbon as catalyst support. In situ characterization techniques proved to be valuable tools to understand carbon gasification mechanism.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Sustainable and/or waste sources for catalysts: Porous carbon development
           and gasification
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Josephine M. Hill
      Catalytic processes can be made even more efficient and sustainable if catalysts are obtained from renewable materials and/or materials that are otherwise viewed as waste. Because the interactions between species are complex, however, unexpected results may be obtained when using impure feedstocks. This paper provides a brief overview of the work that has been done to use wastes to prepare catalysts, followed by a more detailed review of our work with petroleum coke, biomass, and biosolids for porous carbon development and gasification. In particular, the challenges of using these materials are discussed. For example, petroleum coke is a much denser source of carbon than biomass but it also contains more contaminants. Although biomass is generally cleaner, it contains a significant quantity of volatile species so that yields are lower. Biomass is a renewable source of catalysts that can be used through co-feeding to enhance the gasification of other feeds. Spent catalysts can also be a good source of gasification catalysts. Regardless of the source, the catalytic species (e.g., nickel or potassium) can be deactivated by other species present, including vanadium on the spent catalysts or silicon and aluminum that are present in the co-feed.
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      PubDate: 2017-03-15T13:47:27Z
       
  • The role of niobium component in heterogeneous catalysts
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): Maria Ziolek, Izabela Sobczak
      This review article is devoted to the materials containing niobium and modified by the addition of different metals or thio- and amino-organosilanes towards the creation of new surface properties and enhancement of catalytic activity. The intention is to show and discuss the role of niobium supported on molecular sieves in the enhancement of the redox properties of transition metals (copper, silver, gold, platinum) and acidic or basic properties of the catalysts as well as to consider redox properties of pure and modified bulk niobium(V) oxide. This paper covers the contribution to the knowledge of this area brought over the last 15 years by our research team.
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      PubDate: 2017-03-15T13:47:27Z
       
  • Supported, bulk and bulk-supported vanadium oxide catalysts: A short
           review with an historical perspective
    • Abstract: Publication date: 1 May 2017
      Source:Catalysis Today, Volume 285
      Author(s): M. Olga Guerrero-Pérez
      The beginning is a very delicate time for understanding. Concepts are better understood when the student knows the historic perspective. Their minds apprehend the evolution of knowledge and, to some extent, share fundamental discoveries. Students will not understand, for example, the actual model of the structure of an atom if they do not understand first the models proposed by Thomson and Bohr. However, due to the high number of research papers that are nowadays published, sometimes researchers forget to review some of the old papers in which the basis of knowledge were established, and those bases allow to build new achievements, allow to understand where are we, and where are we going. In this context, the main objective of the this article is to present the basis of knowledge regarding supported vanadium oxide catalysts, with an historical point of view. It presents how the main achievements were described in this field, and to do that, the literature century has been reviewed, and especially the progress in the 1980s and 1990s, since the influence of synthesis method and oxide support, the structure of the active phases, and the concept of monolayer were established in those years. The final part of this paper briefly presents the evolution of knowledge that has taken place during the past decade in this field, and some future trends are anticipated.
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      PubDate: 2017-03-15T13:47:27Z
       
  • IFC - Editors; Editorial Board &amp; scope
    • Abstract: Publication date: 15 April 2017
      Source:Catalysis Today, Volume 284


      PubDate: 2017-02-23T13:38:22Z
       
  • Contents list
    • Abstract: Publication date: 15 April 2017
      Source:Catalysis Today, Volume 284


      PubDate: 2017-02-23T13:38:22Z
       
  • Preface – Mat. for photocatalysis
    • Abstract: Publication date: 15 April 2017
      Source:Catalysis Today, Volume 284
      Author(s): Pap Zsolt, Sixto Malato


      PubDate: 2017-02-23T13:38:22Z
       
  • Photocatalytic, photoelectrochemical, and antibacterial activity of
           benign-by-design mechanochemically synthesized metal oxide nanomaterials
    • Abstract: Publication date: 15 April 2017
      Source:Catalysis Today, Volume 284
      Author(s): Gergely F. Samu, Ágnes Veres, Szabolcs P. Tallósy, László Janovák, Imre Dékány, Alfonso Yepez, Rafael Luque, Csaba Janáky
      In the search for highly active and stable photocatalysts, significant efforts are devoted to find both new materials and innovative synthetic methods. In this study, an environmentally friendly and sustainable approach, dry reactive milling, was employed to synthesize two different semiconducting oxide nanomaterials, namely TiO2 and ZnO using polysaccharides as sacrificial templates. The as synthesized nanomaterials were characterized by powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, diffuse reflection UV-vis and Raman spectroscopy, and N2 adsorption tests. Their photocatalytic activity was tested in ethanol degradation, followed by gas chromatographic analysis. Photoelectrochemical measurements were performed to assess the optoelectronic properties and the antimicrobial activity of these photocatalysts was also tested under visible light irradiation. Overall, we found that the performance of the synthesized nanomaterials was comparable to the benchmark P25 EVONIK titania, with ZnO exhibiting a remarkably superior antibacterial activity against E. coli.
      Graphical abstract image

      PubDate: 2017-02-23T13:38:22Z
       
  • Defect engineered visible light active ZnO nanorods for photocatalytic
           treatment of water
    • Abstract: Publication date: 15 April 2017
      Source:Catalysis Today, Volume 284
      Author(s): Tanujjal Bora, Priyanka Sathe, Karthik Laxman, Sergey Dobretsov, Joydeep Dutta
      Photocatalytic degradation of organic wastes and microbes in water using solar light is a green technology that requires the design of visible light active photocatalysts. Here we report the fabrication of visible light active zinc oxide nanorods (ZnO NRs), wherein the visible light absorption is enhanced by modulating the surface defects on the NRs. Oxygen vacancies in the NRs as characterized by photoluminescence and X-ray photoelectron spectroscopy are controlled by annealing at different temperatures in the ambient. The role of surface defects on the visible light photocatalytic degradation of an organic dye, industrial waste, bacterial culture and inland brackish water is studied. Results presented here provide a simple strategy to make the wide bandgap ZnO NRs visible light active, enabling their use for the photocatalytic decontamination of water.
      Graphical abstract image

      PubDate: 2017-02-23T13:38:22Z
       
  • Effect of irradiation intensity and initial pollutant concentration on gas
           phase photocatalytic activity of TiO2 nanotube arrays
    • Abstract: Publication date: 15 April 2017
      Source:Catalysis Today, Volume 284
      Author(s): Paweł Mazierski, Joanna Nadolna, Wojciech Lisowski, Michał J. Winiarski, Maria Gazda, Michał Nischk, Tomasz Klimczuk, Adriana Zaleska-Medynska
      Well-organized TiO2 nanotube arrays were fabricated via one-step anodization process. The as-prepared TiO2 nanotubes were characterized by X-ray powder diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS) and scanning electron microscopy (SEM). Photocatalytic activity of obtained photocatalyst was studied in reaction of toluene degradation in the gas phase using low powered and low cost light-emitting diodes (UV LEDs) as an irradiation source. The effect of irradiation intensity and initial pollutant concentration on gas phase photoactivity of TiO2 nanotubes was analyzed. Obtained TiO2 nanotubes were smooth and vertically oriented with a length of about 1.7±0.05μm. The inner diameter and the wall thickness were 65±2nm and 6±0.4 nm, respectively. The results showed that the initial toluene degradation rate increased (from 0.0062 up to 0.0567μmol/min) with raising initial toluene concentration (50–400ppm), while too high dose of irradiation (about 50mW/cm2) reduced photocatalytic toluene degradation rate. The best stability of TiO2 nanotubes in three subsequent irradiation cycles was observed for irradiation intensity of 38mW/cm2. Moreover, it was found that photocatalytic toluene degradation over TiO2 nanotubes showed first order kinetic behavior.
      Graphical abstract image

      PubDate: 2017-02-23T13:38:22Z
       
  • Improving g-C3N4 photocatalytic performance by hybridizing with Bi2O2CO3
           nanosheets
    • Abstract: Publication date: 15 April 2017
      Source:Catalysis Today, Volume 284
      Author(s): Qitao Zhang, Bin Xu, Saisai Yuan, Ming Zhang, Teruhisa Ohno
      Utilization of semiconductor photocatalysts has been proved to be a cost-effective means for realizing environmental remediation. In this study, visible light-driven Bi2O2CO3/g-C3N4 nanosheets-coupled heterojunction photocatalysts were successfully fabricated via a facile planetary ball milling approach for the first time. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) revealed that an intimate contact interface formed definitely. The crystal phase, characteristic function groups, optical absorption, surface area/porosity, separation of charge carriers, and surface chemical state of the composites were symmetrically investigated by XRD, FTIR, UV-vis, BET-BJH, PL and XPS. It was found that the as-prepared photocatalysts pull double duty to promote the photocatalytic redox activity of CH3CHO, RhB and Cr (VI) degradation, showing 5.6, 4.0 and 2.5 times higher than that of g-C3N4 counterpart, respectively. Such a remarkable enhancement of photocatalytic activity was mainly attributed to the highly efficient separation of charge carriers between the nanosheets-coupled heterojunction interface, enlarged specific surface area and porosity volume, and high content of generated activated oxygen species (H2O2). The results indicate that this universal photocatalyst is a preferential option for photocatalytic degradation of various environmental contaminants.
      Graphical abstract image

      PubDate: 2017-02-23T13:38:22Z
       
  • Photoelectrical response of mesoporous nickel oxide decorated with size
           controlled platinum nanoparticles under argon and oxygen gas
    • Abstract: Publication date: 15 April 2017
      Source:Catalysis Today, Volume 284
      Author(s): Juan Gómez-Pérez, Dorina G. Dobó, Koppány L. Juhász, András Sápi, Henrik Haspel, Ákos Kukovecz, Zoltán Kónya
      The visible light photoelectrical properties of a p-type mesoporous nickel oxide (MNO) support was investigated upon the decoration of size controlled, 1.6nm, 6.4nm and 7.9nm Pt nanoparticles. The near room temperature photoelectrical response of the MNO was 3 times higher after decoration of 1.6nm Pt nanoparticles with a loading of 1wt%. MNO decorated with smaller Pt nanoparticles showed the highest photoresponse. The surrounding atmosphere has striking effect on the photoelectrical behavior, as adsorbed oxygen induced 32% lower photoelectrical response compared to that of argon. The noble metal nanoparticles show both electronic and chemical sensitization: the first functioning as an electron sink resulting in a new band structure of the photocatalyst, and the second interacting chemically with the oxygen and argon adsorbed from the environment. A model is proposed using heterojunctions theory comprising a new induced oxygen potential that may explain the lower photoresponse in the presence of oxygen.
      Graphical abstract image

      PubDate: 2017-02-23T13:38:22Z
       
 
 
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