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Teaching and Learning in Nursing     Full-text available via subscription   (Followers: 8, SJR: 0.313, h-index: 8)
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TĂ©khne : Review of Applied Management Studies     Full-text available via subscription  
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Tetrahedron Letters     Hybrid Journal   (Followers: 27, SJR: 0.933, h-index: 130)
Tetrahedron Organic Chemistry Series     Full-text available via subscription   (Followers: 11)
Tetrahedron: Asymmetry     Hybrid Journal   (Followers: 9)
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The J. of Foot and Ankle Surgery     Full-text available via subscription   (Followers: 10)
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The J. of Supercritical Fluids     Hybrid Journal   (Followers: 3, SJR: 1.141, h-index: 69)
The J. of the American College of Certified Wound Specialists     Hybrid Journal   (Followers: 1, SJR: 0.14, h-index: 3)
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The Leadership Quarterly     Hybrid Journal   (Followers: 410, SJR: 2.069, h-index: 76)
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Theoretical and Applied Fracture Mechanics     Hybrid Journal   (Followers: 7, SJR: 1.179, h-index: 35)
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Theriogenology     Hybrid Journal   (Followers: 2, SJR: 1.059, h-index: 89)
Thermochimica Acta     Hybrid Journal   (Followers: 15, SJR: 0.645, h-index: 77)
Thin Films and Nanostructures     Full-text available via subscription   (Followers: 3)
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Thinking Skills and Creativity     Hybrid Journal   (Followers: 9, SJR: 0.709, h-index: 15)
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Thrombosis Research     Hybrid Journal   (Followers: 25, SJR: 1.098, h-index: 80)
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Tourism Management     Hybrid Journal   (Followers: 12, SJR: 1.961, h-index: 80)
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Toxicology Letters     Hybrid Journal   (Followers: 8, SJR: 1.098, h-index: 101)
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Translational Proteomics     Open Access  
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Transplant Immunology     Hybrid Journal   (Followers: 4, SJR: 0.717, h-index: 48)
Transplantation Proceedings     Hybrid Journal   (Followers: 2, SJR: 0.481, h-index: 63)
Transplantation Reviews     Hybrid Journal   (Followers: 6, SJR: 0.843, h-index: 25)
Transport Policy     Hybrid Journal   (Followers: 10, SJR: 1.666, h-index: 40)
Transportation Geotechnics     Full-text available via subscription   (Followers: 1)

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Journal Cover Catalysis Today
  [SJR: 1.378]   [H-I: 142]   [6 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0920-5861
   Published by Elsevier Homepage  [2801 journals]
  • A novel catalyst of Ni,W-surface-Ti-rich-ETS-10/Al2O3: Its role and
           potential of HDS performance for steric hindered sulfur compound 4,6-DMDBT
           
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Shenyong Ren, Jing Li, Bing Feng, Yandan Wang, Wencheng Zhang, Guangming Wen, Zhihua Zhang, Baojian Shen
      There is growing interest in developing deep hydrodesulfurization (HDS) catalysts to obtain higher activity. This study provides an investigation of influence of surface-Ti-rich-ETS-10 (AT-ETS) on the performance of NiW-based catalyst (NiW-AT-ETS/Al2O3) using NiW-ETS-origin/Al2O3 as the reference. The HDS performance of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) as model sulfur compounds were tested in fixed reactor. NiW-AT-ETS/Al2O3 containing surface-Ti-rich-ETS-10 lowered H2 reduction temperature compared to NiW-ETS-origin/Al2O3. NiW-AT-ETS/Al2O3 had higher WS2 stacking numbers and shorter slab length though they showed similar sulfidation degree. Higher HDS performance was obtained over NiW-AT-ETS/Al2O3 due to higher WS2 slab layers in contrast to NiW-ETS-origin/Al2O3. The advantage of NiW-AT-ETS/Al2O3 for 4,6-DMDBT removal may be also related to easy accessibility of active sites on the catalyst surface as a result of the higher dispersion compared to NiW-ETS-origin/Al2O3.
      Graphical abstract image

      PubDate: 2016-01-28T08:14:14Z
       
  • One-step hydrothermal synthesis of honeycomb 3D graphene-like Co9S8 and
           its catalytic characteristics for NaHCO3 reduction by H2S
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Baoyun Hu, Zhenzi Jing, Junjie Fan, Guodong Yao, Fangming Jin
      Honeycomb 3D graphene-like Co9S8 nanocrystallines were successfully synthesized using cobalt and Na2S·9H2O as starting materials without a template via a simple hydrothermal route. The composition, structure, morphology, and catalytic activity of the as-prepared Co9S8 were characterized by investigation of XRD, SEM, EDS, XPS, GC–MS and HPLC. It was found that an appropriate concentration of inexpensive NaHCO3 play a critical role for the formation of honeycomb Co9S8 nanocrystallines. On the other hand, Co9S8 acted as a catalyst in the hydrothermal reaction, producing formic acid reduced from NaHCO3 as high as 3680mg/L. It indicates that the present study not only proposes a simple way of honeycomb Co9S8 synthesis, but also provides a potential approach to CO2 reduction.
      Graphical abstract image

      PubDate: 2016-01-28T08:14:14Z
       
  • Reactivity of levulinic acid during aqueous, acid-catalyzed HMF hydration
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Shruti Karwa, Varun M. Gajiwala, Jacob Heltzel, Sushil K.R. Patil, Carl R.F. Lund
      In 0.1M sulfuric acid at 125°C, levulinic acid did not form humins, and if HMF was present, levulinic acid was not incorporated in the humins that formed from it. Levulinic acid was converted to unidentified products believed to include angelica lactones, at a rate more than 500 times smaller than the rate of HMF conversion. Quantum chemical calculations indicate that at reaction conditions, levulinic acid is protonated to form protonated dihydro-5-hydroxy-5-methyl-2(3H)-furanone which is very stable. Very small amounts of levulinic acid and 5-hydroxy-γ-valerolactone may be present in equilibrium with this cation. Angelica lactones can then be formed from 5-hydroxy-γ-valerolactone in an acidic aqueous environment.
      Graphical abstract image

      PubDate: 2016-01-28T08:14:14Z
       
  • Efficient conversion of dimethyl phthalate to phthalide over CuO in
           aqueous media
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Jun Fu, Dezhang Ren, Lu Li, Yunjie Liu, Fangming Jin, Zhibao Huo
      An efficient conversion of dimethyl phthalate (DMP) to phthalide (PHT) over CuO in aqueous media was investigated. Among the catalysts we tested, various metals or metal oxides were effective for the conversion of DMP to PHT in water, and CuO showed excellent catalytic activity and gave the best result. The PHT yield of 85% was achieved when Zn acted as a reductant. Mechanism study for the conversion of DMP suggested that an intermediate 2-hydroxymethyl benzoic acid was produced in the process. The present study provides a useful route for the production of PHT from DMP.
      Graphical abstract image

      PubDate: 2016-01-28T08:14:14Z
       
  • Importance of Pd monomer pairs in enhancing the oxygen reduction reaction
           activity of the AuPd(100) surface: A first principles study
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Hyung Chul Ham, Gyeong S. Hwang, Jonghee Han, Sung Pil Yoon, Suk Woo Nam, Tae Hoon Lim
      Based on density functional theory calculations, we present that pairs of 1st nearest Pd monomers play an important role in significantly enhancing the oxygen reduction reaction (ORR) on the AuPd(100) surface. While the catalytic ORR activity tends to be sensitive to the surface atomic ordering, we find that the Pd monomer pairs lead to a substantial reduction in the activation barrier for O/OH hydrogenation with no significant suppression of O–O bond scission, thereby considerably lowering the overall activation energy for the ORR as compared to the case of pure Pd(100). On the other hand, an isolated Pd monomer tends to greatly suppress the O–O bond cleavage reaction, which in turn slows down the ORR kinetics. Unlike the monodentate adsorption of O2 on an isolated Pd monomer, the pairing of Pd monomers allows O2 adsorption in a bidentate configuration and consequently facilitating O–O bond scission. However, the barrier for OH hydrogenation at each Pd site shows no significant change between the isolated and paired cases, while it is noticeably lower than the pure Pd case.
      Graphical abstract image

      PubDate: 2016-01-28T08:14:14Z
       
  • Synthesis of quinoline derivatives from anilines and aldehydes catalyzed
           by Cp2ZrCl2 and recyclable Cp2ZrCl2/MCM-41 system
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Qiaoxia Guo, Lijun Liao, Weiling Teng, Shenyong Ren, Xiao Wang, Yingying Lin, Fanfang Meng
      A facile method for the synthesis of quinoline derivatives using catalytic amount of Cp2ZrCl2 or Cp2ZrCl2 supported on MCM-41 (Cp2ZrCl2/MCM-41) in reaction of anilines and aldehydes is described. When Cp2ZrCl2/MCM-41 was used as catalyst, the yields of quinolines were enhanced by 5–15% compared with Cp2ZrCl2 as catalyst alone under the same reaction conditions. More importantly, Cp2ZrCl2/MCM-41 catalyst can be reused at least thrice by simple recover via filtration in air. Moreover, both Cp2ZrCl2 and Cp2ZrCl2/MCM-41 showed good catalytic activities to generate corresponding quinoline derivatives in moderate to good yields by varying the substituent of aniline and aldehyde. And the reaction conditions were optimized by studying the influences of reactant ratio, additives, solvent effect and reaction temperatures.
      Graphical abstract image

      PubDate: 2016-01-28T08:14:14Z
       
  • Spectroscopic characterization and catalytic activity of Rh supported on
           CeO2-modified Al2O3 for low-temperature steam reforming of propane
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Yan Li, Xiaoxing Wang, Chunshan Song
      The present work aims at clarifying the effects of CeO2 addition to Al2O3 support on the surface chemical characteristics and catalytic activity of supported Rh catalysts for low-temperature steam reforming of propane. Steam reforming of propane was carried out at 500°C over Rh catalysts supported on alumina modified with different CeO2 loading (0, 5, 10, 20, 50, 75, and 100wt%). The Rh catalyst supported on 20wt% CeO2-modified alumina (2Rh/20CeAl) showed the highest propane and steam conversions, followed in decreasing order by those with 10, 5, 50, 75, 0, and 100wt% CeO2. TPR results show that the interaction between ceria and rhodium improves the reducibility of both rhodium oxide and ceria. XPS analysis indicates strong ceria–alumina interaction and strong Rh-support interaction for Rh catalysts with CeO2 loading less than 20wt%. Field-Emission SEM and AES results revealed that at 20wt% CeO2 loading, ceria was dispersed as separate nano-particles with sizes of 100–200nm on the alumina surface. At high CeO2 loading (≥50wt%) ceria particles formed conglomerates covering alumina surface. The 2Rh/20CeAl catalyst showed the highest activity for propane steam reforming possibly because the high CeO2 dispersion created a large area of ceria–alumina interface which helped increase Rh dispersion, and the strong interaction between Rh and support helped enhance the reducibility of ceria and rhodium oxide. Rh loaded onto the interfacial region of ceria and alumina is considered to be most active for the 2Rh/20CeAl catalyst.
      Graphical abstract image

      PubDate: 2016-01-28T08:14:14Z
       
  • Hydrothermal conversion of glucose into lactic acid with sodium silicate
           as a base catalyst
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Jia Duo, Zhengshuai Zhang, Guodong Yao, Zhibao Huo, Fangming Jin
      In this paper, the hydrothermal conversion of glucose to lactic acid (LA) using sodium silicate (Na2SiO3) as a mild base catalyst was investigated. The results showed that Na2SiO3 was effective catalyst for the conversion of glucose. The highest LA yield of about 30% was obtained from glucose with a lower concentration of Na2SiO3 at 300°C for 60s. It was also found that the use of Na2SiO3 led to a much less corrosion and a higher LA yield than that with NaOH at the same pH value. This process provides an environmentally friendly and highly effective method toward the synthesis of useful LA from glucose.
      Graphical abstract image

      PubDate: 2016-01-28T08:14:14Z
       
  • Studies on Ni–M (M=Cu, Ag, Au) bimetallic catalysts for selective
           hydrogenation of cinnamaldehyde
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Murthiyamma Gengatharan Prakash, Rajaram Mahalakshmy, Konda Ramaswamy Krishnamurthy, Balasubramanian Viswanathan
      Bimetallic catalysts of the type Ni–M with M=Cu, Ag and Au, and supported on TiO2-P-25 have been prepared by chemical reduction using glucose as the reducing agent. Hydrogenation of cinnamaldehyde (CAL) to yield hydrocinnamaldehyde (HCAL), cinnamyl alcohol (COL) and hydrocinnamyl alcohol (HCOL) has been studied on the catalysts in the temperature range 60–140°C and at 20kg/cm2 pressure, with methanol as solvent. Ni crystallite sizes, measured by X-ray line broadening analysis (XLBA), H2 pulse chemisorption and Transmission Electron Microscope (TEM) techniques, are in the range 8–12nm. Temperature Programmed Reduction (TPR) and Diffuse Reflectance Spectroscopic (DRS) studies indicate the formation of Ni–Cu alloys, while Ni–Ag and Ni–Au exist as bimetallic nanoparticles. High-resolution HRTEM studies show that the bimetallic nanoparticles are in close contact, forming hetero junctions. Changes in the XPS binding energy values for Ni 2p1/2 and Ni 2p3/2 levels reveal that Cu/Ag/Au, tend to increase electron density around Ni, which retards the adsorption of CAL via olefinic bond and weakens NiH bond strength. H2 TPD measurements also indicated weakening of NiH bond. Bimetallic catalysts display higher CAL conversion and selectivity to COL vis-à-vis the corresponding monometallic catalysts at lower reaction temperatures, 60–80°C. But, selectivity to COL decreases at higher temperatures, 100–120°C. Mode of adsorption of CAL and nature of adsorbed hydrogen on bimetallic catalysts influence their activity and selectivity.
      Graphical abstract image

      PubDate: 2016-01-28T08:14:14Z
       
  • Contents list
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263




      PubDate: 2016-01-28T08:14:14Z
       
  • Eli Ruckenstein—A model for science and engineering research
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Yun Hang Hu



      PubDate: 2016-01-28T08:14:14Z
       
  • How to stabilize highly active Cu+ cations in a mixed-oxide catalyst
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Kumudu Mudiyanselage, Si Luo, Hyun You Kim, Xiaofang Yang, Ashleigh E. Baber, Friedrich M. Hoffmann, Sanjaya Senanayake, Jose A. Rodriguez, Jingguang G. Chen, Ping Liu, Darío J. Stacchiola
      Mixed-metal oxides exhibit novel properties that are not present in their isolated constituent metal oxides and play a significant role in heterogeneous catalysis. In this study, a titanium-copper mixed-oxide (TiCuO x ) film has been synthesized on Cu(111) and characterized by complementary experimental and theoretical methods. At sub-monolayer coverages of titanium, a Cu2O-like phase coexists with TiCuO x and TiO x domains. When the mixed-oxide surface is exposed at elevated temperatures (600–650K) to oxygen, the formation of a well-ordered TiCuO x film occurs. Stepwise oxidation of TiCuO x shows that the formation of the mixed-oxide is faster than that of pure Cu2O. As the Ti coverage increases, Ti-rich islands (TiO x ) form. The adsorption of CO has been used to probe the exposed surface sites on the TiOx–CuO x system, indicating the existence of a new Cu+ adsorption site that is not present on Cu2O/Cu(111). Adsorption of CO on Cu+ sites of TiCuO x is thermally more stable than on Cu(111), Cu2O/Cu(111) or TiO2(110). The Cu+ sites in TiCuO x domains are stable under both reducing and oxidizing conditions whereas the Cu2O domains present on sub-monolayer loads of Ti can be reduced or oxidized under mild conditions. The results presented here demonstrate novel properties of TiCuO x films, which are not present on Cu(111), Cu2O/Cu(111), or TiO2(110), and highlight the importance of the preparation and characterization of well-defined mixed-metal oxides in order to understand fundamental processes that could guide the design of new materials.
      Graphical abstract image

      PubDate: 2016-01-28T08:14:14Z
       
  • IFC - Editorial Board
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263




      PubDate: 2016-01-28T08:14:14Z
       
  • Effect of N3− species on selective acetylene hydrogenation over
           Pd/SAC catalysts
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Maocong Hu, Xianqin Wang
      Selective hydrogenation of acetylene to ethylene is very important for removing a trace amount of acetylene from ethylene. Tuning catalyst acidity is critical for hydrogenation reaction to prevent oligomerization. In this work, NaN3 was introduced to Pd catalyst serving as Lewis base sites. NaN3-Pd/SAC catalysts with different N3 − loadings (0–15wt.%) were prepared by impregnation method and analyzed with BET, temperature-programmed reduction (TPR), Fourier-transferred Infrared (FTIR) spectroscopy, CO pulse chemisorption, temperature-programmed desorption (TPD) of hydrogen and acetylene. The results showed NaN3 covered some Pd species and increased the reduction temperatures of catalysts. Also NaN3 addition decreased the catalyst surface areas due to blocking some pores on the support. N3 − on the catalysts lowered hydrogen adsorption capacity but showed superior adsorption capability for acetylene, the selectivity and conversion of the acetylene hydrogenation was negatively affected by N3 − species under the current operation conditions. The amount of the adsorbed hydrogen and the types of acetylene adsorption played important roles for the hydrogenation reaction. This work provides insights on how to prepare an effective catalyst for removing acetylene impurity from ethylene.
      Graphical abstract image

      PubDate: 2016-01-28T08:14:14Z
       
  • The state of iron sites in the calcined FeAlPO4-5 and its tuning to the
           property of microporous AlPO4-5 molecular sieve
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Bing Feng, Jiangcheng Li, Xiaochun Zhu, Qiaoxia Guo, Wencheng Zhang, Guangming Wen, Zhihua Zhang, Lin Gu, Zhenzhong Yang, Qinghua Zhang, Baojian Shen
      The dispersion and coordination is critical to the nature of metal phases. This article describes an approach of single Fe sites preparing under microporous environment via calcination of the Fe incorporated FeAlPO4-5 as well as the tuning to the property of AlPO4-5 molecular sieve. The UV, Raman, EPR spectroscopies and H2-TPR characterization revealed through the extraction of framework Fe inside the micropore by calcination, extra-framework Fe sites were generated, the dispersion of which was higher than Fe sites of impregnated Fe2O3/AlPO4-5, and it indicated that part of Fe sites of FeAlPO4-5 can be with coordination vacancy. It is notable that the presence of single Fe sites was directly observed by Cs-corrected STEM micrograph. NH3-TPD and toluene-TPD results both exhibited an enhanced acidity and π bond adsorption ability of FeAlPO4-5 toward AlPO4-5 and the impregnated sample Fe2O3/AlPO4-5. Finally, the FeAlPO4-5 turned out to perform higher thiophene desulfurization rate against AlPO4-5 and impregnated sample, which can be related to the improvement in the adsorption ability and reactivity for the single Fe sites inside the microporous environment.
      Graphical abstract image

      PubDate: 2016-01-28T08:14:14Z
       
  • Oxidative dehydrogenation of isobutane over vanadia catalysts supported by
           titania nanoshapes
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Shannon Kraemer, Adam J. Rondinone, Yu-Tong Tsai, Viviane Schwartz, Steven H. Overbury, Juan-Carlos Idrobo, Zili Wu
      Support plays a complex role in catalysis by supported metal oxides and the exact support effect still remains elusive. One of the approaches to gain fundamental insights into the support effect is to utilize model support systems. In this paper, we employed for the first time titania nanoshapes as the model supports and investigated how the variation of surface structure of the support (titania, TiO2) impacts the catalysis of supported oxide (vanadia, VO x ). TiO2 truncated rhombi, spheres and rods were synthesized via hydrothermal method and characterized with XRD and TEM. These TiO2 nanoshapes represent different mixtures of surface facets including [101], [010] and [001] and were used to support vanadia. The structure of supported VO x species was characterized in detail with in situ Raman spectroscopy as a function of loading on the three TiO2 nanoshapes. Oxidative dehydrogenation (ODH) of isobutane to isobutene was used as a model reaction to test how the support shape influences the activity, selectivity and activation energy of the surface VO x species. It was shown that the shape of TiO2 support does not pose evident effect on either the structure of surface VO x species or the catalytic performance of surface VO x species in isobutane ODH reaction. This insignificant support shape effect was ascribed to the small difference in the surface oxygen vacancy formation energy among the different TiO2 surfaces and the multi-faceting nature of the TiO2 nanoshapes.
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      PubDate: 2016-01-28T08:14:14Z
       
  • Evaluation of Rh/CexTi1−xO2 catalysts for synthesis of oxygenates
           from syngas using XPS and TPR techniques
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Ephraim Sheerin, Gunugunuri K. Reddy, Panagiotis Smirniotis
      Rh/Ce x Ti1−x O2 catalysts have been investigated for the synthesis of ethanol from syngas. For this purpose various Ce x Ti1−x O2 (x =0, 0.25, 0.5, 0.75, and 1) solid solution supports were synthesized using co-precipitation, which is an inexpensive and environmental friendly method. 2wt% Rh has been deposited over these supports by using wet impregnation method. We have evaluated these Rh catalysts for synthesis of ethanol from syngas at atmospheric pressure and 350psi. Among, the various catalysts, Rh supported on Ce0.75Ti0.25O2 catalyst exhibit better selectivity toward oxygenates compared to other catalysts. Interestingly, Ti rich samples exhibit higher selectivity toward hydrocarbons while Ce rich samples exhibit higher selectivity toward oxygenated products. The catalytic results at atmospheric pressure show that titania rich catalysts exhibit higher H2 conversion and ceria rich catalysts exhibit higher CO-conversion at 250°C at atmospheric pressure. Temperature programmed reduction measurements suggest that Rh promotes the cerium surface reduction. X-ray photoelectron measurements show that all the catalysts exhibit peaks due to Ce4+ and Ce3+ oxidations states in the Ce 3d spectra. O1s spectra of activated Rh/TiO2 and Rh/Ce0.5Ti0.5O2 catalysts show two peaks after reduction in hydrogen. One peak is due to the oxygen atoms from the individual oxides and the other peak is from the compound formation between Rh and the support. X-ray photoelectron measurements of activated catalysts also show that Rh/Ce0.5Ti0.5O2 catalyst exhibit higher Rh1+ ions on the surface compared to Rh/TiO2 and exhibits better selectivity toward oxygenated products.
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      PubDate: 2016-01-28T08:14:14Z
       
  • Hydrogen bonding-inspired organocatalysts for CO2 fixation with epoxides
           to cyclic carbonates
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Xiao-Fang Liu, Qing-Wen Song, Shuai Zhang, Liang-Nian He
      Carboxyl-containing organocatalysts, e.g. EDTA (ethylenediaminetetraacetic acid) in combination with nucleophilic halide such as nBu4NBr were demonstrated to be efficient catalyst systems for the synthesis of cyclic carbonates from CO2 and a broad range of epoxides in excellent yield and selectivity. Thanks to synergistic effects of carboxylic groups and bromide anion, the cycloaddition reaction proceeded smoothly at 5bar CO2 under mild reaction conditions. Interaction of carboxylic groups in EDTA with the epoxide via hydrogen bonding presumably facilitates the ring-opening of the epoxide by the nucleophile e.g. bromide. In particular, multiple carboxylic groups in one molecule i.e. EDTA could more effectively activate the epoxide and stabilize the alkoxide intermediate through multi-site hydrogen bonding in comparison with monocarboxylic acid. Moreover, the carboxylic acid like EDTA used in this study represents a cheap, commercially available, environmentally benign, metal-free catalyst for CO2 conversion. Thus, this catalytic protocol could have potential application for catalytic fixation of CO2 into value-added chemicals.
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      PubDate: 2016-01-28T08:14:14Z
       
  • Recent progresses in the size and structure control of MOF supported noble
           metal catalysts
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Yueping Zhang, You Zhou, Yue Zhao, Chang-jun Liu
      The preparation, characterization and application of metal organic framework (MOF) supported noble metal catalysts have drawn a great interest with the rapid progresses in the syntheses of MOFs and MOF based composites. There are several principal objectives for the investigation of MOF supported catalysts, including (1) the designable frameworks provide us a very clear model for the fundamental catalytic studies; (2) the extremely large surface area and the extremely high porosity of MOFs are always attractive for the catalytic applications; (3) the designable or the controllable porous structure with uniform pore size is excellent for the preparation of designable catalyst, a dream of chemists and chemical engineers worldwide; (4) the MOFs can be easily modified by various functional groups; (5) MOF based composites (with graphene and other materials) can be easily fabricated; (6) the needs for novel catalysts keep growing; (7) the member of the MOF family increases remarkably recently with the improvement of thermal and chemical stability of MOFs; (8) the hybrid of noble metal catalysts and MOFs is leading to many unusual catalytic properties. In this perspective, we summarize the recent advances in the preparation and application of MOF supported noble metal catalysts. To prepare this kind of new catalysts, two general methods have been reported: the precursor way and the metal nanoparticle way. The former is based on metal ions or metal precursors like inorganic salt (nitrate or chloride) or metallorganic compound. The metal ions or metal precursors have to be loaded into the MOF framework via chemical vapor infiltration, solution impregnation and incipient wetness infiltration or to be pre-incorporated on the organic linkers before the synthesis of MOF. The second way is based on the pre-synthesized metal nanoparticles. To do so, the pre-synthesized metal nanoparticles have to be directly involved in the synthesis of MOFs from the beginning. The characteristics of two ways have been discussed. Because of the unique properties and the structure of MOFs, the loading of metal or metal ion with the assistance of organic solvent is very helpful for the confinement of nanoparticles within the cavities of MOF frameworks or for control of size and location of nanoparticles. The structure control of catalyst together with size and location control still remains a significant challenge.
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      PubDate: 2016-01-28T08:14:14Z
       
  • Ceria-supported nickel borate as a sulfur-tolerant catalyst for
           autothermal reforming of a proxy jet fuel
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Lei Liu, Liang Hong
      Catalytic reforming of liquid hydrocarbons to produce H2-enriched fuel in an auxiliary power unit is essential to the operation of fuel cell on board. This study explored ceria-supported nickel borate [Ni3(BO3)2] catalyst for conducting the above reaction under autothermal reforming (ATR) condition. In the present catalytic system operating at 750°C and under purge stream of feed, nickel borate undergoes partial degradation whose degree depends on the type of support used to release catalytically reactive tiny Ni0 metal crystallite and B2O3. To achieve a high fuel conversion (>95%), it is crucial to maintain a dominant ratio of nickel borate versus Ni0 nanocrystallites as the reactive site. Typically, more than 90% nickel borate remains on the Y-doped ceria (CYO) while almost all nickel borate degrade to Ni0 and B2O3 on the Gd-doped ceria (CGO) after 24h ATR of the proxy fuel comprising dodecane, naphthalene (10wt%) and thiophene (containing 100pm S). In consequence, the former catalyst shows a higher fuel conversion profile than the latter by 15–20%. It is proposed that nickel borate itself is a cocatalyst to induce cracking of fuel molecules, which provides smaller hydrocarbon species for the reforming on Ni0 crystallites, and promotes sulfur tolerance of Ni0 crystallites to a large extent on CYO according to the XPS and NMR characterizations.
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      PubDate: 2016-01-28T08:14:14Z
       
  • The water-gas shift reaction for hydrogen production from coke oven gas
           over Cu/ZnO/Al2O3 catalyst
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Chunling Wang, Cheng Liu, Wei Fu, Zhenghong Bao, Jieyu Zhang, Weizhong Ding, Kuochih Chou, Qian Li
      A study of H2-rich syngas derived from coke oven gas for hydrogen production on Cu/ZnO/Al2O3 catalyst has been performed by water-gas shift reaction (WGSR). The theoretical thermodynamic equilibrium on the reaction temperature, steam/carbon (S/C) ratio and the high amount of H2 and CH4 in the syngas have been considered in this work. From theoretical calculations and experiment results, it can be seen that the catalyst Cu/ZnO/Al2O3 can effectively and selectively transform H2O and CO to H2 and CO2 under an atmosphere of 2.5vol.% CH4 and 75.0vol.% H2. The high catalytic activity is closely correlated with the strong structural interaction of aurichalcite and hydrotalcite phases. Moreover, the thermal stability of the Cu/ZnO/Al2O3 catalyst was also studied by calcining at different temperatures. No obvious decrease in CO conversion was detected, suggesting that the catalyst had high heat-resisting ability due to the enhancement of the synergistic interaction in structural precursors.
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      PubDate: 2016-01-28T08:14:14Z
       
  • Different reaction sequences for partial oxidation of propane over
           different ceria-supported catalysts
    • Abstract: Publication date: 1 April 2016
      Source:Catalysis Today, Volume 263
      Author(s): Dady B. Dadyburjor, Tapan Das, Mayuri Mukka, Edwin L. Kugler
      Hydrogen production using the partial oxidation of propane over supported metal catalysts was studied in a small isothermal packed-bed reactor. Ceria was used as the support, due to its ability to store and release oxygen, with nickel and platinum being the metals used. The overall purpose of the study was to determine the pathways and sequences of hydrogen production. Flow rates of the inlet stream were varied from 100 to 400 scc/min, and two weights of each catalyst were used. The reactions were carried out at 600°C and 1 atm, with a ratio of O2 to C3H8 maintained at 1.78. For the experimentally observed products leaving the reactor, the corresponding reaction matrix was subjected to Gauss elimination to determine that four independent reactions could be obtained. This results in a maximum of ten sets of these reactions. The number of sets was reduced by carrying out a material balance on the products to determine the net rate of each of the four reactions; sets containing negative rates for irreversible reactions could then be eliminated from consideration. To determine the validity of any remaining sets containing dry-reforming, steam-reforming and water-gas shift reactions, a secondary set of experiments were carried out at the outlet conditions of the original experiments to see if those three reactions could indeed take place. Eventually, only one set of four reactions was deemed suitable for the Pt/CeO2 catalyst, incorporating total oxidation, partial oxidation, dehydrogenation and water formation. The extents of these four reactions were followed as a function of contact time, showing that partial oxidation decreases down the reactor, while total oxidation increases. For the Ni/CeO2 catalyst, three sets were suitable. The three are very similar, in that they all contain total oxidation, steam reforming and dehydrogenation, with the fourth reaction being partial oxidation, dry reforming or water formation. Qualitatively, the same results are found for all three sets. Total oxidation is the predominant reaction at all contact times, with steam reforming and/or dry reforming producing hydrogen only at larger contact times. The differences between the results for the two supported catalysts indicate that different types of reactors should be chosen, depending upon the catalyst to be used. For supported nickel catalysts, large packed-bed reactors may be optimal, while micro-reactors in parallel may be best for supported platinum catalysts.
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      PubDate: 2016-01-28T08:14:14Z
       
  • IFC - Editorial Board
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262




      PubDate: 2015-12-09T09:45:16Z
       
  • Probing active sites in iron-based catalysts for oxygen electro-reduction:
           A temperature-dependent 57Fe Mössbauer spectroscopy study
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Moulay Tahar Sougrati, Vincent Goellner, Anna K. Schuppert, Lorenzo Stievano, Frédéric Jaouen
      Two Fe-N-C electrocatalysts for oxygen reduction were studied by 57Fe Mössbauer-spectroscopy between 300 and 5K. The first catalyst contains almost exclusively FeN x C y moieties while the second contains additional crystalline phases, i.e. metallic iron and iron carbide. The Mössbauer parameters of two quadrupole doublets named D1 and D2, attributed to low and medium spin FeN4/C moieties, respectively, do not change with temperature down to 5K. This indicates that such moieties do not undergo phase transition or magnetic ordering, supporting the view that the active sites are localized on isolated iron atoms. At room temperature, the Lamb-Mössbauer factors of doublets D1 and D2 are 0.46 and 0.52, smaller than those of α-Fe (0.67) and γ-Fe (0.78). These values allow for the first time a precise Mössbauer quantification of Fe species in Fe-N-C catalysts. The ORR activity is best correlated with the absolute content of the FeN4/C moiety associated with doublet D1, assigned to a FeIIN4/C moiety in low-spin state. The ORR turnover frequency of such moieties is however known to depend on chemical and electronic properties of the carbon matrix, which will require additional descriptor(s) than the site density in order to precisely interpret the ORR activity of such materials.
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      PubDate: 2015-12-09T09:45:16Z
       
  • DFT calculations on electro-oxidations and dissolutions of Pt and
           Pt–Au nanoparticles
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Ryosuke Jinnouchi, Kensaku Kodama Takahisa Suzuki, Yu Morimoto
      DFT calculations were carried out on electro-oxidations and dissolutions of pure Pt and Pt–Au nanoparticles. Calculations indicated that electro-oxidations are initiated by OH adsorbate formations at (100)-edges of the pure Pt nanoparticle of 260 atoms at 0.5V (RHE). The formed OH adsorbates are replaced by O adsorbates at 0.75V, and the formed O adsorbates aggregate at (110)-edges of the nanoparticle to form 1-dimensional PtO2 chains. Further increase in the electrode potential causes gradual increases in O adsorbates at the facets of the nanoparticle, and the formed O atoms start sinking into the subsurfaces to form α-PtO2 monolayers at 1.18V. Calculations indicated that the edges of the pure Pt nanoparticle were covered too strongly with the O adsorbates at 0.9V to allow for adsorptions of oxygen molecules at those surface sites. Pt atoms located at the edges were, therefore, judged to be inactive for oxygen reduction reaction (ORR). The Pt atoms located at the edges were also shown to be easily dissolved into the solutions because they do not have strong binding energies with the particle. Further calculations on the Pt–Au nanoparticle indicated that the corrosive Pt dissolutions can be suppressed by subtitutional introductions of Au atoms at the edges of the nanoparticle without lowering ORR activity.
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      PubDate: 2015-12-09T09:45:16Z
       
  • Contents list
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262




      PubDate: 2015-12-09T09:45:16Z
       
  • Electrocatalysis for sustainable energy conversion or electrocatalysis
           today
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Aliaksandr Bandarenka, Karl J.J. Mayrhofer



      PubDate: 2015-12-09T09:45:16Z
       
  • pH dependence of OER activity of oxides: Current and future perspectives
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Livia Giordano, Binghong Han, Marcel Risch, Wesley T. Hong, Reshma R. Rao, Kelsey A. Stoerzinger, Yang Shao-Horn
      Understanding the mechanism of the oxygen evolution reaction (OER) is essential to develop better electrocatalysts for solar fuel generation. Measuring the pH dependence of the OER activity can provide insights on the reaction path that are otherwise difficult to access experimentally, in particular on the coupling of protons and electrons during the reaction. We argue that the use of a pH-dependent reference electrode, such as the reversible hydrogen electrode, is more suitable for these studies as it assures that the overpotential is fixed while varying the pH. We provide criteria for pH dependence when this reference is used and validate the existing results with our measurements on RuO2 powders. A statistical analysis of the existing results allows us to sketch trends in the reaction order on pH with respect to the number of d electrons, oxidation states, and crystal families, providing the groundwork for future OER mechanistic studies on oxides.
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      PubDate: 2015-12-09T09:45:16Z
       
  • Double layer effects in electrocatalysis: The oxygen reduction reaction
           and ethanol oxidation reaction on Au(111), Pt(111) and Ir(111) in alkaline
           media containing Na and Li cations
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Pietro P. Lopes, Dusan Strmcnik, Jakub S. Jirkovsky, Justin G. Connell, Vojislav Stamenkovic, Nenad Markovic
      Oxygen reduction and ethanol oxidation reactions were studied on Au(111), Pt(111) and Ir(111) in alkaline solutions containing sodium and/or lithium cations. By keeping the same (111) surface orientation and exploring oxophilicity trends and non-covalent interactions between OHad and alkali metal cations (AMC n+), we were able to gain deep insights into the multiple roles that OHad plays in these important electrocatalytic reactions. Cyclic voltammetry experiments revealed that OHad formation initiates at distinct electrode potentials, governed by the oxophilicity of the specific metal surface, with further OHad adlayer stabilization by non-covalent alkali-cation interactions and affecting the formation of a “true oxide” layer at higher electrode potentials. Although OHad is a simple spectator for the ORR, it promotes the ethanol oxidation reaction (EOR) at lower potentials and act as spectator at high OHad coverages. By changing the alkali metal cation at the interface (Li+) on more oxophilic surfaces, it was possible to promote the EOR even more, relative to Na+, without changing the product distribution for the reaction. This cation effect suggests that OHad–Li+(H2O) x clusters can stabilize the ethoxide adlayer, thus improving the EOR activity. Our results indicate the importance of the entire electrochemical interface in determining the electrocatalytic activity during reaction.
      Graphical abstract image Highlights

      PubDate: 2015-12-09T09:45:16Z
       
  • Role of the interfacial water structure on electrocatalysis: Oxygen
           reduction on Pt(111) in methanesulfonic acid
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Andrea P. Sandoval-Rojas, Ana M. Gómez-Marín, Marco F. Suárez-Herrera, Víctor Climent, Juan M. Feliu
      Most of electrocatalytic reactions occur in an aqueous environment. Understanding the influence of water structure on reaction dynamics is fundamental in electrocatalysis. In this work, the role of liquid water structure on the oxygen reduction at Pt(111) electrode is analyzed in methanesulfonic (MTSA) and perchloric acids. This is because these different anions can exert a different influence on liquid water structure. Results reveal a lower ORR electrode activity in MTSA than in HClO4 solutions and they are discussed in light of anion's influence on water structural ordering. From them, the existence of an outer-sphere, rate determining, step in the ORR mechanism is suggested.
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      PubDate: 2015-12-09T09:45:16Z
       
  • Molecular modeling of the proton density distribution in a water-filled
           slab-like nanopore bounded by Pt oxide and ionomer
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Amin Nouri-Khorasani, Kourosh Malek, Ali Malek, Tetsuya Mashio, David P. Wilkinson, Michael H. Eikerling
      A slab-like pore model consisting of a thin water slab that is confined by a metal wall on one side and a dense ionomer skin layer on the other side was simulated with classical molecular dynamics. The model mimics thin-film structures of Pt/support (referred to as the metal), water layer, and ionomer phase encountered in cathode catalyst layers of polymer electrolyte fuel cells. The equilibrium proton density near the metal surface is the key variable required to predict the ORR activity and the Pt dissolution rate under fuel cell operating conditions. Here, we explored the equilibrium proton density distribution in the confined water layer as a function of oxide coverage at the metal surface, excess surface charge density, water layer thickness, and ionomer film structure. The effect of ionomer hydrophobicity on the water dynamics in the nanopore was also investigated. The electric dipole field created by the oxide layer on the Pt surface interacts strongly with protons, and concentrates protons at the metal surface. A direct relation was found between the surface proton concentration and the oxide layer dipole moment. Performing simulations with different ionomer structures and pore widths clarified the sensitivity of the proton density distribution to properties that are specific for the structure and distribution of the ionomer phase in catalyst layers.
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      PubDate: 2015-12-09T09:45:16Z
       
  • Structure-sensitive electroreduction of acetaldehyde to ethanol on copper
           and its mechanistic implications for CO and CO2 reduction
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Isis Ledezma-Yanez, Elena Pérez Gallent, Marc T.M. Koper, Federico Calle-Vallejo
      Ethanol is a highly desirable product of the electrochemical reduction of CO and/or CO2 on copper. Although ethanol and ethylene share common intermediates at the early stages of CO/CO2 reduction to C2 species on copper, the pathways bifurcate and most copper surfaces favor the formation of ethylene. We present here a combined experimental-computational study of the electroreduction of acetaldehyde to ethanol on Cu(111), Cu(100) and Cu(322). The experiments show structure-sensitive onset potentials for acetaldehyde reduction such that lower overpotentials are observed for more open facets (η 322 <η100 <η111). Our DFT calculations show that the electrochemical reduction of acetaldehyde proceeds via a CH3CH2O* intermediate on the three electrodes at high *H coverage, and that the stability of this weakly bound intermediate determines the onset potential. Our results suggest that during the late stages of CO/CO2 reduction to C2 species on copper, ethanol formation has higher energetic barriers than ethylene formation, and hence the selectivity is inclined toward the latter. Importantly, our results suggest that the barriers for ethanol formation can be lowered by making use of its structure sensitivity.
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      PubDate: 2015-12-09T09:45:16Z
       
  • Pathways to ultra-low platinum group metal catalyst loading in proton
           exchange membrane electrolyzers
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Katherine E. Ayers, Julie N. Renner, Nemanja Danilovic, Jia X. Wang, Yu Zhang, Radenka Maric, Haoran Yu
      Hydrogen is one of the world's most important chemicals, with global production of about 50billion kg/year. Currently, hydrogen is mainly produced from fossil fuels such as natural gas and coal, producing CO2. Water electrolysis is a promising technology for fossil-free, CO2-free hydrogen production. Proton exchange membrane (PEM)-based water electrolysis also eliminates the need for caustic electrolyte, and has been proven at megawatt scale. However, a major cost driver is the electrode, specifically the cost of electrocatalysts used to improve the reaction efficiency, which are applied at high loadings (>3mg/cm2 total platinum group metal (PGM) content). Core–shell catalysts have shown improved activity for hydrogen production, enabling reduced catalyst loadings, while reactive spray deposition techniques (RSDT) have been demonstrated to enable manufacture of catalyst layers more uniformly and with higher repeatability than existing techniques. Core–shell catalysts have also been fabricated with RSDT for fuel cell electrodes with good performance. Manufacturing and materials need to go hand in hand in order to successfully fabricate electrodes with ultra-low catalyst loadings (<0.5mg/cm2 total PGM content) without significant variation in performance. This paper describes the potential for these two technologies to work together to enable low cost PEM electrolysis systems.
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      PubDate: 2015-12-09T09:45:16Z
       
  • On the pH dependence of electrochemical proton transfer barriers
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Jan Rossmeisl, Karen Chan, Egill Skúlason, Mårten E. Björketun, Vladimir Tripkovic
      The pH dependence of rate of the hydrogen evolution/oxidation reaction HER/HOR is investigated. Based on thermodynamic considerations, a possible explanation to the low exchange current for hydrogen reactions in alkaline is put forward. We propose this effect to be a consequence of the change in configurational entropy of the proton as it approaches the surface. As a proton crosses the outer Helmholtz plane, it will lose a fraction of its entropy before it can interact with the electrode surface, which gives rise to an entropic barrier. The size of this barrier will depend on the electrostatic environment in the double layer region. The entropic barrier can be rate determining only when the surface catalysis is fast. Therefore the effect of pH is most pronounced on good catalysts and for fast reactions. This entropic barrier is also in a good agreement with the unusually low prefactor measured in experiments of good catalysts such as Pt. In such catalysts, the enthalpy barrier of 0.1–0.2eV of the rate-determining step does not come from any of the surface reactions (Volmer, Tafel or Heyrovsky) but instead from the proton transfer into the outer Helmholtz layer.
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      PubDate: 2015-12-09T09:45:16Z
       
  • The colloidal tool-box approach for fuel cell catalysts: Systematic study
           of perfluorosulfonate-ionomer impregnation and Pt loading
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Jozsef Speder, Alessandro Zana, Matthias Arenz
      In this study, the correlation between the impregnation of proton exchange membrane fuel cell catalysts with perfluorosulfonate-ionomer (PFSI) and its electrochemical and electrocatalytic properties is investigated for different Pt loadings and carbon supports using a rotating-disk electrode (RDE) setup. We concentrate on its influence on the electrochemical surface area (ECSA) and the oxygen reduction reaction (ORR) activity. For this purpose, platinum (Pt) nanoparticles are prepared via a colloidal based preparation route and supported on three different carbon supports. Based on RDE experiments, we show that the ionomer has an influence both on the Pt utilization and the apparent kinetic current density of ORR. The experimental data reveal a strong interaction in the microstructure between the electrochemical properties and the surface properties of the carbon supports, metal loading and ionomer content. This study demonstrates that the colloidal synthesis approach offers interesting potential for systematic studies for the optimization of fuel cell catalysts.
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      PubDate: 2015-12-09T09:45:16Z
       
  • Evaluation of kinetic constants on porous, non-noble catalyst layers for
           oxygen reduction—A comparative study between SECM and hydrodynamic
           methods
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Anna Dobrzeniecka, Aleksandar R. Zeradjanin, Justus Masa, Magdalena Blicharska, Daniela Wintrich, Pawel J. Kulesza, Wolfgang Schuhmann
      An advanced approach based on scanning electrochemical microscopy (SECM) was used to investigate the kinetics of the oxygen reduction reaction (ORR) on multiwalled carbon nanotubes (MWCNTs) and a composite of MWCNTs and cobalt (IX) protoporphyrin (MWCNTs/CoP). The amount of hydrogen peroxide produced during ORR was studied as a function of catalyst loading in an electrolyte of pH 7. Additionally, a Pt ultra microelectrode (UME) was used to determine changes in interfacial oxygen concentration from which intrinsic rate constants of heterogeneous electron transfer during the ORR were calculated. The amount of hydrogen peroxide produced and the number of electrons exchanged during oxygen reduction, and the heterogeneous electron transfer rate constants determined using SECM were compared with the corresponding values obtained using methods based on forced convection, namely RRDE and RDE. It was found that SECM offers some advantages compared to RDE or RRDE with regard to accuracy in determining the number of electrons transferred during the ORR, particularly in the case of thick and porous catalyst films. However, the heterogeneous electron transfer rate constants were similar for both methods, indicating that the determination of the surface concentration of reactants using RC-SECM suffers from some drawbacks.
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      PubDate: 2015-12-09T09:45:16Z
       
  • Dynamical changes of a Ni-Fe oxide water splitting catalyst investigated
           at different pH
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Mikaela Görlin, Manuel Gliech, Jorge Ferreira de Araújo, Sören Dresp, Arno Bergmann, Peter Strasser
      Mixed Ni-Fe oxide electrocatalysts have shown high catalytic activity for the oxygen evolution reaction (OER) in alkaline electrolyte. Fundamental research on mixed Ni-Fe OER catalysts has largely focused on high pH, while the OER activity near neutral pH has remained poorly studied. Here we review the activity of an amorphous mixed Ni-Fe oxyhydroxide catalyst supported on carbon (NiFeO x /C) in 0.1M KOH pH 13, in 0.1M borate buffer (B i ) pH 9.2, and in 0.1M phosphate buffer (P i ) pH 7.0. The OER catalytic performance was found to decrease in the order of pH 13>pH 9.2>pH 7. In contrast to pH 13 and 9.2, the catalyst cycled in pH 7 showed an instantaneous decrease in OER activity and a simultaneous loss of the Ni(OH)2/NiOOH redox peak. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) showed the formation of crystalline areas upon CV cycling, which appeared more Ni enriched after cycling in pH 7. Deactivated electrodes cycled in pH 13 recovered the OER activity along with a partial reappearance of the Ni redox peak when subsequently cycled in pH 13. SEM-EDX spectroscopy confirmed compositional changes in the bulk during cycling at different pH, with an extensive leaching of Ni in pH 7. Our study provides new insight into the OER activity upon exposure to different electrolyte conditions, which unveils a highly dynamic Ni-Fe oxide framework.
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      PubDate: 2015-12-09T09:45:16Z
       
  • Fine-tuning the activity of oxygen evolution catalysts: The effect of
           oxidation pre-treatment on size-selected Ru nanoparticles
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Elisa Antares Paoli, Federico Masini, Rasmus Frydendal, Davide Deiana, Paolo Malacrida, Thomas W. Hansen, Ib Chorkendorff, Ifan E.L. Stephens
      Water splitting is hindered by the sluggish kinetics of the oxygen evolution reaction (OER). The choice of materials for this reaction in acid is limited to the platinum group metals; high loading required of these scarce and expensive elements severely limit the scalability of such technology. Ruthenium oxide is among the best catalysts for OER, however the reported activity and stability can vary tremendously depending on the preparation conditions and pre-treatment. Herein, we investigate the effect of oxidation treatment on mass-selected Ru nanoparticles in the size range between 2 and 10nm. The effect of two distinct oxidation pre-treatments on the activity and stability have been investigated: (1) thermal oxidation; and (2) oxidation with an oxygen plasma under vacuum. We report that activity and stability can be tuned by using different oxidation pre-treatments. Thermally oxidized particles exhibited the lowest activity, although over an order of magnitude higher than the state of the art, and the highest stability. Plasma-treated particles showed intermediate performance between as-deposited and thermally oxidized NPs.
      Graphical abstract image

      PubDate: 2015-12-09T09:45:16Z
       
  • Influence of the electrolyte composition on the activity and selectivity
           of electrocatalytic centers
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Viktor Colic, Marcus D. Pohl, Daniel Scieszka, Aliaksandr S. Bandarenka
      The capability to efficiently design new electrocatalytic materials depends on a deeper understanding of all factors influencing the performance of active sites under reaction conditions. While the electrode surface structure and composition are primary, the role of electrolyte components in the activity and selectivity of catalytic centers is also significant, if not drastic. Interestingly, the performance of electrocatalysts is not only affected by the so-called specifically adsorbing ions. Many species, which are generally considered “inert”, can de facto change the key properties of the catalytic sites. However, the origin of such experimentally observed effects is often poorly understood. Despite the fact that certain trends are frequently observed, further investigation of model systems and development in the field of quantum chemistry calculations are necessary in order to gain deeper insight into the effects of the electrolyte composition. The goal of this review article is to summarize and analyze recent achievements in the elucidation of the non-trivial effects of electrolyte components and their contribution to the observed performance of catalytic centers. A particular focus is set on the influence of (i) alkali metal cations, (ii) commonly used anions, (iii) unexpected pH effects, as well as (iv) the impact of certain ionic liquids on the activity and selectivity of catalytic systems. Reactions which are essential for the prospective sustainable energy provision schemes are selected as illustrative examples.
      Graphical abstract image

      PubDate: 2015-12-09T09:45:16Z
       
  • Protection of inorganic semiconductors for sustained, efficient
           photoelectrochemical water oxidation
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Michael F. Lichterman, Ke Sun, Shu Hu, Xinghao Zhou, Matthew T. McDowell, Matthew R. Shaner, Matthias H. Richter, Ethan J. Crumlin, Azhar I. Carim, Fadl H. Saadi, Bruce S. Brunschwig, Nathan S. Lewis
      Small-band-gap (E g <2eV) semiconductors must be stabilized for use in integrated devices that convert solar energy into the bonding energy of a reduced fuel, specifically H2(g) or a reduced-carbon species such as CH3OH or CH4. To sustainably and scalably complete the fuel cycle, electrons must be liberated through the oxidation of water to O2(g). Strongly acidic or strongly alkaline electrolytes are needed to enable efficient and intrinsically safe operation of a full solar-driven water-splitting system. However, under water-oxidation conditions, the small-band-gap semiconductors required for efficient cell operation are unstable, either dissolving or forming insulating surface oxides. We describe herein recent progress in the protection of semiconductor photoanodes under such operational conditions. We specifically describe the properties of two protective overlayers, TiO2/Ni and NiO x , both of which have demonstrated the ability to protect otherwise unstable semiconductors for >100h of continuous solar-driven water oxidation when in contact with a highly alkaline aqueous electrolyte (1.0M KOH(aq)). The stabilization of various semiconductor photoanodes is reviewed in the context of the electronic characteristics and a mechanistic analysis of the TiO2 films, along with a discussion of the optical, catalytic, and electronic nature of NiO x films for stabilization of semiconductor photoanodes for water oxidation.
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      PubDate: 2015-12-09T09:45:16Z
       
  • Facile synthesis of palladium phosphide electrocatalysts and their
           activity for the hydrogen oxidation, hydrogen evolutions, oxygen reduction
           and formic acid oxidation reactions
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Anthony R.J. Kucernak, K.F. Fahy, V. N. Naranammalpuram Sundaram
      We demonstrate a new approach for producing highly dispersed supported metal phosphide powders with small particle size, improved stability and increased electrocatalytic activity towards some useful reactions. The approach involves a one-step conversion of metal supported on high surface area carbon to the metal phosphide utilising a very simple and scalable synthetic process. We use this approach to produce PdP2 and Pd5P2 particles dispersed on carbon with a particle size of 4.5–5.5nm by converting a commercially available Pd/C powder. The metal phosphide catalysts were tested for the oxygen reduction, hydrogen oxidation and evolution, and formic acid oxidation reactions. Compared to the unconverted Pd/C material, we find that alloying the P at different levels shifts oxide formation on the Pd to higher potentials, leading to greater stability during cycling studies (20% more ECSA retained, 5k cycles) and in thermal treatment under air. Hydrogen absorption within the PdP2 and Pd5P2 particles is enhanced. The phosphides compare favourably to the most active catalysts reported to date for formic acid oxidation, especially PdP2, and there is a significant decrease in poisoning of the surface compared to Pd alone. The mechanistic changes in the reactions studied are rationalised in terms of increased water activation on the surface phosphorus atoms of the catalyst. One of the catalysts, PdP2/C is tested in a fuel cell as anode and cathode catalyst and shows good performance.
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      PubDate: 2015-12-09T09:45:16Z
       
  • Oxygen and hydrogen evolution reactions on Ru, RuO2, Ir, and IrO2 thin
           film electrodes in acidic and alkaline electrolytes: A comparative study
           on activity and stability
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Serhiy Cherevko, Simon Geiger, Olga Kasian, Nadiia Kulyk, Jan-Philipp Grote, Alan Savan, Buddha Ratna Shrestha, Sergiy Merzlikin, Benjamin Breitbach, Alfred Ludwig, Karl J.J. Mayrhofer
      Metallic iridium and ruthenium as well as their oxides are among the most active oxygen evolution (OER) electrocatalysts in acidic media, and are also of interest for the catalysis of the hydrogen evolution (HER). The stability of these materials under different operating conditions is, however, still not fully understood. In the current work, activity and stability of well-defined Ru, RuO2, Ir, and IrO2 thin film electrodes are evaluated in acidic and alkaline electrolytes using an electrochemical scanning flow cell (SFC) connected to an inductively coupled plasma mass spectrometer (ICP-MS). Identical experimental protocols are intentionally employed for all electrodes and electrolytes, to obtain unambiguous and comparable information on intrinsic activity and stability of the electrodes. It is found that independent of the electrolyte, OER activity decreases as Ru>Ir≈RuO2 >IrO2, while dissolution increases as IrO2 ≪RuO2 <Ir≪Ru. Moreover, dissolution of these metals in both solutions is 2–3 orders of magnitude higher compared to their respective oxides, and dissolution is generally more intense in alkaline solutions. Similarly to the OER, metallic electrodes are more active catalysts for HER. They, however, suffer from dissolution during native oxide reduction, while IrO2 and RuO2 do not exhibit significant dissolution. The obtained results on activity and stability of the electrodes are discussed in light of their potential applications, i.e. water electrolysers or fuel cells.
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      PubDate: 2015-12-09T09:45:16Z
       
  • Pt/IrO2–TiO2 cathode catalyst for low temperature polymer
           electrolyte fuel cell – Application in MEAs, performance and
           stability issues
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Alexandra Pătru, Annett Rabis, Sandra Elizabeth Temmel, Rüdiger Kotz, Thomas Justus Schmidt
      This work addresses the long-term stability issues of polymer electrolyte fuel cells (PEFC) based on a new oxide supported cathode catalyst generation using commercial Pt/IrO2–TiO2 (Umicore®) as model cathode catalyst. First, the ionomer to oxide supported cathode catalyst ratio has been studied and optimized. The amount of Nafion® ionomer was varied in the electrode composition and an optimum was found for 10wt% ionomer content with respect to the catalyst weight allowing for an optimum triple phase boundary in the gas diffusion electrodes. The initial performance of the MEAs based on the Pt/IrO2–TiO2 catalyst was found to be equivalent to those of Pt/high surface area carbon (HSAC) catalyst. In order to study the stability of the catalytic layers, the manufactured MEAs were exposed to accelerated stress test protocols designed for automotive fuel cell applications. These protocols are simulating the catalyst behaviour during vehicle acceleration and deceleration and during vehicle start-up and shut down triggering respectively platinum dissolution and support corrosion. These experiments were performed in 30cm2 single PEFCs using state-of-the-art catalyst Pt/HSAC (TKK®) for comparison. Specifically in the start–stop related test protocol, the new IrO2–TiO2 catalyst support exhibits remarkable stability with only 25mV cell potential loss at 0.8A/cm2 after 10,000 cycles, whereas the carbon supported Pt catalyst could not reach this current density anymore under these conditions. Moreover a structural catalyst modification is pointed out to occur during the in situ stability tests.
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      PubDate: 2015-12-09T09:45:16Z
       
  • Polydimethylsiloxane treated cathode catalyst layer to prolong hydrogen
           fuel cell lifetime
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Myounghoon Choun, Daniyar Nauryzbayev, Dongyoon Shin, Jaeyoung Lee
      In operation of hydrogen fuel cells for vehicle, carbon corrosion induced by frequent on/off operation significantly causes degradation of performance and durability of fuel cells, aggregating and losing Pt particles. It is critical to develop durable cathode and understand the mechanism of degradation in hydrogen fuel cells for commercialization. In this study, we prepared polydimethylsiloxane treated cathode, which is hydrophobic, for improving durability in hydrogen fuel cells. In addition, effect of hydrophobic cathode on durability was investigated by various analyses. We observed that the polydimethylsiloxane (PDMS) treated cathode contributed to limit both mass transfer limitation and carbon corrosion by efficient water withdrawal. Based on our results, we provide the possibility of PDMS treatment to decline the performance degradation in fuel cells.
      Graphical abstract image

      PubDate: 2015-12-09T09:45:16Z
       
  • Atomic-scale restructuring of hollow PtNi/C electrocatalysts during
           accelerated stress tests
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Laetitia Dubau, Miguel Lopez-Haro, Julien Durst, Frédéric Maillard
      Hollow nanomaterials composed of a Pt-rich shell surrounding a central void have demonstrated promising electrocatalytic activity for the oxygen reduction reaction (ORR). However, their long-term stability remains understudied, and is the focus of the present paper. Here, we followed the temperature-dependent morphological and compositional trajectories of hollow PtNi/C nanoparticles during accelerated stress tests (AST) of interest for proton-exchange membrane fuel cells (PEMFC) applications. The combined physical, chemical and electrochemical results showed that: (i) the PtNi/C nanoparticles preserve a hollow nanostructure during accelerated stress testing at T =25°C, but collapsed in real PEMFC operating conditions (solid electrolyte – T =80°C), (ii) the dissolution of Ni atoms is drastically enhanced with an increase of the temperature, almost all Ni atoms being leached after the AST conducted in a single PEMFC, (iii) a lattice strain of ca. 0.4% persists in the aged hollow PtNi/C nanocatalysts, (iv) whatever the AST conditions, hollow PtNi/C nanocatalysts show improved ORR activity over solid Pt/C nanocatalysts of the same crystallite size. The catalytic enhancement is believed to result from the presence of subsurface vacancies in the dealloyed hollow PtNi/C nanoparticles. In a more global perspective, the present contribution emphasizes the crucial role of temperature on the stability of shape-controlled particles (far from their equilibrium shape).
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      PubDate: 2015-12-09T09:45:16Z
       
  • Ultra-low mass loading of platinum nanoparticles on bacterial cellulose
           derived carbon nanofibers for efficient hydrogen evolution
    • Abstract: Publication date: 15 March 2016
      Source:Catalysis Today, Volume 262
      Author(s): Yan Mi, Liaoyong Wen, Zhijie Wang, Dawei Cao, Huaping Zhao, Yilong Zhou, Fabian Grote, Yong Lei
      The ultra-low loading amount of Pt nanoparticles on three-dimensional bacterial cellulose derived carbon nanofibers (BCF) was achieved by using a modified atomic layer deposition (ALD) process for hydrogen evolution reaction (HER). The only 5 cycles of ALD led to a high dispersion of Pt nanoparticles on BCF surfaces with an average size of 2nm, possessing an as low as 0.87wt% of mass loading. The HER catalytic performance revealed that the as-prepared Pt/BCF have good catalytic activity and stability. The present work provides a general strategy for minimizing the demand of precious-metal catalysts while maintaining their high catalytic efficiency.
      Graphical abstract image

      PubDate: 2015-12-09T09:45:16Z
       
  • IFC - Editorial Board
    • Abstract: Publication date: 1 March 2016
      Source:Catalysis Today, Volume 261




      PubDate: 2015-12-01T06:29:09Z
       
  • Contents list
    • Abstract: Publication date: 1 March 2016
      Source:Catalysis Today, Volume 261




      PubDate: 2015-12-01T06:29:09Z
       
  • Professor Calvin H. Bartholomew
    • Abstract: Publication date: 1 March 2016
      Source:Catalysis Today, Volume 261




      PubDate: 2015-12-01T06:29:09Z
       
  • On the selectivity to higher hydrocarbons in Co-based
           Fischer–Tropsch synthesis
    • Abstract: Publication date: 1 March 2016
      Source:Catalysis Today, Volume 261
      Author(s): Erling Rytter, Nikolaos E. Tsakoumis, Anders Holmen
      Impact of process variables on selectivity to C5+ products during cobalt Fischer–Tropsch synthesis (FTS) are summarized and discussed, comprising temperature; pressure; synthesis gas composition; transport limitations of synthesis gas and products; conversion of CO; and effect of water. Further, effect of catalyst formulation, preparation and activation is included, specifically catalyst synthesis; cobalt crystallite size; crystal structure of cobalt; distribution of crystallites; support materials; pore structure; acidity; surface modifications; reduction and pretreatment. Other topics comprise promoters with focus on reduction promoters including rhenium and nickel; impurities like alkali and sulphur; deactivation and regeneration. Discussion is based on mechanistic understanding, specifically kinetics based on hydrogen assisted CO dissociation; a linear relationship between CH4 and C5+ products; possible reinsertion of olefins; hydrogenation of olefins; and surface coverage based on SSITKA data. It is concluded that the majority of reported data on FTS can be rationalized in terms of a CH x pool mechanism on cobalt where x shifts toward monomers and high polymerization probability (α-value); or methane and light products formation, depending on synthesis conditions and catalyst properties. Selectivity responses are illustrated mainly based on cobalt catalysts on transition alumina supports. How the support in itself affects C5+ selectivity is challenging. There clearly is a change in the composition of the cobalt surface pool of reaction intermediates, but how this change originates in support properties remains to be illuminated. So far there is no direct evidence for the termination process; β-hydrogen abstraction, to play a major role in determining FTS selectivity.
      Graphical abstract image

      PubDate: 2015-12-01T06:29:09Z
       
 
 
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