Applied Catalysis A, General (v.507, #C)

Contents (iii-vii).

Comparative study for low temperature water-gas shift reaction on Pt/ceria catalysts: Role of different ceria supports by Rishabh Jain; Altug S. Poyraz; David P. Gamliel; Julia Valla; Steven L. Suib; Radenka Maric (1-13).
Display OmittedPt on ceria catalysts for water-gas shift (WGS) reaction were prepared by employing three ceria nanopowders synthesized with different processing techniques and having different surface area and porosities. Nano-Pt (∼0.5–2 nm) was deposited in the vapor phase onto each of the three ceria supports by Reactive Spray Deposition Technology (RSDT). The catalysts were performance tested for the WGS reaction in the temperature range of 150–450 °C at a gas hourly space velocity (GHSV) of 13,360 h−1. The structure–activity relationship for the ceria-based materials was studied. The most promising catalyst was Pt supported on mesoporous ceria with crystallite size of 5.8 nm and Brunauer–Emmett–Teller (BET) surface area of 187 m2/g. This configuration demonstrated complete CO conversion at 225 °C. The CO adsorption strength and the ability to dissociate H2O are the two main factors that determine the activity of a particular catalyst site for the water-gas shift (WGS) reaction. This study leads to the conclusion that the highest water-gas shift reaction activity was obtained on Pt supported on the mesoporous ceria with low crystallite size and high surface area, with well dispersed Pt, leading to enhanced Pt–ceria interaction.
Keywords: Water-gas shift reaction; Flame spray pyrolysis; Pt–ceria interface; Mesoporous ceria; Processing–structure–property relationship;

Spectroscopic, calorimetric, and catalytic evidences of hydrophobicity on Ti-MCM-41 silylated materials for olefin epoxidations by Joaquín Silvestre-Alberó; Marcelo E. Domine; José L. Jordá; María T. Navarro; Fernando Rey; Francisco Rodríguez-Reinoso; Avelino Corma (14-25).
Display OmittedHydrophobic Ti-MCM-41 samples prepared by post-synthesis silylation treatment demonstrate to be highly active and selective catalysts in olefins epoxidation by using organic hydroperoxides as oxidizing agents in liquid phase reaction systems. Epoxide yields show important enhancements with increased silylation degrees of the Ti-mesoporous samples. Catalytic studies are combined and correlated with spectroscopic techniques (e.g. XRD, XANES, UV-Visible, 29Si MAS-NMR) and calorimetric measurements to better understand the changes in the surface chemistry of Ti-MCM-41 samples due to the post-synthesis silylation treatment and to ascertain the role of these trimethylsilyl groups incorporated in olefin epoxidation. In such manner, the effect of the organic moieties on solids, and both water and glycol molecules contents on the catalytic activity and selectivity are analyzed in detail. Results show that the hydrophobicity level of the samples is responsible for the decrease in water adsorption and, consequently, the negligible formation of the non-desired glycol during the catalytic process. Thus, catalyst deactivation by glycol poisoning of Ti active sites is greatly diminished, this increasing catalyst stability and leading to practically quantitative production of the corresponding epoxide. The extended use of these hydrophobic Ti-MCM-41 catalysts together with organic hydroperoxides for the highly efficient and selective epoxidation of natural terpenes is also exemplified.
Keywords: Hydrophobic materials; Ti-MCM-41 catalyst; Silylation treatment; Immersion calorimetry; Catalytic epoxidation;

Room temperature hydrogenation of furfuryl alcohol by Pd/titanate nanotube by Qingqing Yuan; Feiyang Ye; Teng Xue; Yejun Guan (26-33).
Display OmittedThe liquid phase hydrogenation of furfuryl alcohol to tetrahydrofurfuryl alcohol at room temperature under 1 atm hydrogen was succeeded on a TiO2 nanotube (TNT) supported palladium catalyst. The palladium nanoparticles in size of 2–8 nm were loaded by the deposition-reduction method with NaBH4 as reducing reagent. The Pd/TNT catalyst showed high dispersion as revealed by CO chemisorption and improved catalytic performance in terms of both furfuryl alcohol conversion and tetrahydrofurfuryl alcohol selectivity, probably attributed to the unique electronic interaction between Pd metals and TNT surface containing sodium cations. Among the catalysts investigated, 5.8 wt.% Pd/TNT showed the best performance, with 98% conversion and 98% selectivity to tetrahydrofurfuryl alcohol in ethanol.
Keywords: Palladium; Furfuryl alcohol; Hydrogenation; Tetrahydrofurfuryl alcohol; Titanate nanotube;

Deactivation study of supported Pt catalyst on glycerol hydrogenolysis by Manuel Checa; Alberto Marinas; José M. Marinas; Francisco J. Urbano (34-43).
Display OmittedDifferent Pt-based systems (5% by weight) were obtained through impregnation of chloroplatinic acid on Al2O3, CeO2, La2O3 and ZnO. The solids were tested for glycerol hydrogenolysis. Results showed that metal sites are needed both for dehydration of glycerol and subsequent reduction to 1,2-propanediol (1,2-PDO). Moreover, as the reaction proceeds there is a progressive decrease in 1,2-PDO yield as a consequence of acetol oligomerization which already takes place at temperatures as low as 150 °C. Among all tested supports, ZnO was the one exhibiting better characteristics for glycerol selective transformation into 1,2-PDO as a result of the combination of the appropriate surface acidity, limited deactivation and stability under hydrothermal working conditions.
Keywords: Glycerol hydrogenolysis; Supported Pt catalysts; Support effect; 1,2-Propanediol; Catalyst Deactivation; Catalysts fouling;

Catalytic cracking of carinata oil for hydrocarbon biofuel over fresh and regenerated Zn/Na-ZSM-5 by Xianhui Zhao; Lin Wei; Shouyun Cheng; Yuhe Cao; James Julson; Zhengrong Gu (44-55).
Display OmittedCatalytic cracking of carinata oil over fresh and regenerated Zn/Na-ZSM-5 catalyst in a fixed-bed reactor at 450 °C was carried out to produce hydrocarbon biofuel. The effect of the fresh and regenerated Zn/Na-ZSM-5 on the hydrocarbon biofuel’s quality and yield was discussed. Characterization of the catalyst, hydrocarbon biofuel and gas were carried out. The hydrocarbon biofuel yield obtained over regenerated Zn/Na-ZSM-5 increased but the coke yield and distillation residual yield decreased, compared to fresh Zn/Na-ZSM-5. The regeneration of Zn/Na-ZSM-5 had a minor influence on the density of the hydrocarbon biofuel, but the higher heating value (HHV) decreased, and the viscosity and acid value increased over regenerated Zn/Na-ZSM-5. The regeneration of Zn/Na-ZSM-5 reduced the decarboxylation, decarbonylation and dehydrogenation of carinata oil, which caused the lower content of CO2, CO, H2 and light hydrocarbons (C1–C5). A preliminary test of the distillation residual mixture upgrading over fresh Zn/Na-ZSM-5 was performed, suggesting that the distillation residual mixture could be recycled for further upgrading. The produced gas including H2, CO and light hydrocarbons might be reused as syngas for ether power generation or production of value chemicals.
Keywords: Catalytic cracking; Carinata oil; Hydrocarbon biofuel; Zn/Na-ZSM-5; Regeneration; Distillation residual;

Methanol oxidative decomposition over zirconia supported silver catalyst and its reaction mechanism by Naohiro Shimoda; Shota Umehara; Masaki Kasahara; Teruhisa Hongo; Atsushi Yamazaki; Shigeo Satokawa (56-64).
Display OmittedTo develop a new catalyst for catalytic decomposition of volatile organic compounds (VOCs), the activity of various oxide supported silver (Ag) based catalysts for methanol (MeOH) oxidation reaction have been evaluated. Based on the activity evaluation, zirconia (ZrO2) is considered to be a substitute to ceria (CeO2) as a support material. The ZrO2 supported catalyst loading Ag component can oxidize MeOH to CO2 completely, while the main product is CO for MeOH oxidation over pure ZrO2. In the present work, 2.0 wt.% Ag/ZrO2 exhibits excellent activity comparable to Ag/CeO2. Furthermore, according to in situ FT-IR analysis over Ag/ZrO2 and pure ZrO2, it is considered that the methoxy, formate, and bicarbonate species adsorbed on the ZrO2 surface are intermediate species. We thus deduce that Ag component significantly enhances the oxidation step of methoxy species to CO2 via formate species, leading to the complete oxidation of MeOH to CO2 over Ag/ZrO2 catalyst.
Keywords: Methanol oxidation; Ag catalyst; VOCs; Zirconia; FTIR;

Display OmittedNanostructured magnesium doped manganese oxides (Mg-SC-OMS-2) was prepared through doping Mg into OMS-2 using an ultrasound-assisted approach. This Mg-SC-OMS-2 material showed low crystallinity with a large surface area and extensive defects which are totally different from those synthesized by conventional method. Extraordinarily high NO removal performance was obtained. It retained 99% NO removal ratio for as long as 8 h under extremely high space velocity of 120,000 mL/g/h. More attractively, when water vapor was introduced, above 50% removal ratio of catalyst was maintained for as long as 250 h. The high catalytic activity of Mg-SC-OMS-2 is associated with presence of redox pair Mn3+/Mn4+ and activated oxygen species at oxygen vacancies occurring via the pathway of Mars-van Krevelen mechanism.
Keywords: NOx; Magnesium; Manganese oxide OMS; Catalytic oxidation;

Display OmittedThree cobalt–copper catalysts singly promoted with La, Zr, or Al were studied for catalytic conversion of syngas to higher alcohols. The properties of the promoted catalysts have been characterized by TPR, XRD, XPS and BET. CO hydrogenation was carried out in a plug-flow reactor under 30 bar, GHSV = 36000 scc/gcat/h, H2/CO = 2, and 250 °C at differential conversions. The catalyst activity and selectivity to higher alcohols are greatest on CuCoLa2O​3: ethanol selectivity 10.5% at a conversion of 0.76%. During 9 h of time-on-stream, CO conversion decreased on CuCoLa2O3​ while methanol and higher alcohol selectivity increased. The behaviors on CuCoZrO2 and CuCoAl2O3 were different. On these two catalysts, CO conversion and selectivity reached a near-steady state much more quickly than CuCoLa2O3. These results suggest changes on CuCoLa2O3 that increase the selectivity for oxygenates continue with time, at least over the time scale investigated here.
Keywords: Higher alcohols synthesis; Syngas; Cobalt; Copper; Metal oxide promoters; Modified Fischer–Tropsch catalysts;

Excellent catalytic performance, thermal stability, and water resistance of 3DOM Mn2O3-supported Au–Pd alloy nanoparticles for the complete oxidation of toluene by Shaohua Xie; Jiguang Deng; Yuxi Liu; Zhenhua Zhang; Huanggen Yang; Yang Jiang; Hamidreza Arandiyan; Hongxing Dai; Chak Tong Au (82-90).
Display OmittedThree-dimensionally ordered macroporous (3DOM) Mn2O3-supported AuPd y alloy (xAuPd y /3DOM Mn2O3; x  = 1.0–3.8 wt%; Pd/Au molar ratio : y  = 1.85, 1.92) catalysts were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods, respectively. Physicochemical properties of the samples were characterized by means of numerous techniques, and their catalytic activities were evaluated for toluene oxidation. It is found that the AuPd y alloy nanoparticles (NPs) with an particle size of 2–4 nm were uniformly dispersed on the surface of 3DOM Mn2O3, and the 3.8AuPd1.92/3DOM Mn2O3 sample performed the best: the temperature at 90% toluene conversion was 162 °C at 40,000 mL/(g h). Furthermore, the 3.8AuPd1.92/3DOM Mn2O3 sample was highly active even after calcination at 700 °C. The introduction of water vapor to the feedstock induced a positive effect on toluene oxidation over 3.8AuPd1.92/3DOM Mn2O3, but a negative effect over 1.9Au/3DOM Mn2O3 or 1.9Pd/3DOM Mn2O3. The excellent catalytic activity, thermal stability, and water resistance of 3.8AuPd1.92/3DOM Mn2O3 were associated with its good activation adsorption of oxygen on AuPd1.92 NPs and strong interaction between noble metal NPs and 3DOM Mn2O3. The 3DOM Mn2O3-supported AuPd y alloy NPs are promising industrial catalysts for efficient removal of volatile organic compounds.
Keywords: Three-dimensionally ordered macroporous manganese oxide; Au–Pd alloy nanoparticle; Toluene oxidation; Thermal stability; Water resistance;

Effect of the irradiation wavelength on the performance of nanoporous carbon as an additive to TiO2 by Marta A. Andrade; Ana S. Mestre; Rocío J. Carmona; A.P. Carvalho; Conchi O. Ania (91-98).
Display OmittedWe report the dependence of the photochemical activity of titania/carbon hybrid catalysts toward the degradation of phenol from solution using polychromatic light and filters. In all cases larger photooxidative efficiencies were obtained using light at 200 nm <  λ  < 600 nm. The incorporation of a carbon additive to TiO2 increased the photocatalytic performance regardless the illumination conditions, although, the effect was more pronounced at λ  > 200 nm. The photocatalytic runs carried out with the nonporous carbon alone confirmed a certain level of intrinsic photoactivity under both irradiation conditions. Nevertheless, a clear deactivation was evident after 60 min of irradiation suggesting that the photoactive sites in the carbon are either consumed or deactivated in the course of the reaction. The composition of the catalyst and the illumination conditions also have a strong effect on the nature of the degradation intermediates, with a marked regioselectivity toward ortho-substitution at high energy photons and when the carbon component is added to the catalyst composition.
Keywords: Sisal-based nanoporous carbons; TiO2/carbon photocatalysts; UV and visible light; Phenol photocatalytic degradation;

Display OmittedTiO2–carbon and vanadium–TiO2–carbon composite nanofibrous membranes were synthesized through electrospinning and investigated for the complete oxidation of low-concentration acetone. The novel nanofibrous membranes were characterized through various techniques, including TG/DSC, SEM-EDX, HRTEM, XRD, N2 sorption, XPS, NH3-TPD, and H2-TPR analyses. Introduction of vanadium at an appropriate amount enhances the catalytic performance in complete acetone oxidation. The best result was obtained with 10V–TiC nanofibers that contain 10 wt.% vanadium. Furthermore, the 10V–TiC nanofibers displayed higher activity than that of the V2O5/TiO2 reference catalyst prepared by impregnation method. Characterization results indicate that these fibers exhibit a typical nanofibrous morphology. Vanadium incorporation accelerates the decomposition of the gel precursor nanofibers and causes variations in textural properties, surface chemistry, acidity, and reducibility. The high porosity of the nanofibrous structure, abundant adsorbed oxygen species on the surface, strong acidity, and reducibility enhance the catalytic performance.
Keywords: TiO2–carbon; Electrospinning; Nanofibers; Volatile organic compounds; Catalytic oxidation;

Porous NiO nano-sheet as an active and stable catalyst for CH4 deep oxidation by Fan Yu; Xianglan Xu; Honggen Peng; Huajiang Yu; Yanfeng Dai; Wenming Liu; Jiawei Ying; Qi Sun; Xiang Wang (109-118).
Display OmittedA series of polycrystalline NiO catalysts with different morphologies have been prepared in this study with a simple precipitation method by changing the precipitants, and used for CH4 deep oxidation. NiO-NaOH, a sample prepared with NaOH solution, displays the highest CH4 oxidation activity among all the catalysts, which is competitive to that of 0.5 wt.% Pd/Al2O3, especially at high WHSV. SEM demonstrates that it consists of uniform nano-sheets with an average thickness around 23 nm. Compared with other two samples composed of irregular nano-particles, this nano-sheet mesoporous sample possesses higher surface area, larger pore volume and pore size. H2-TPR demonstrates that it also contains less Ni3+ cations, which are found to be harmful to the activity. Furthermore, it is revealed that more active oxygen species has been formed on the surface of this nano-sheet sample. As a result, NiO-NaOH shows the highest CH4 oxidation activity among all the NiO catalysts. Water vapour has no any negative effect on the activity of NiO-NaOH, as testified by the long-term stability test in the presence of water vapour.
Keywords: NiO catalysts; Nano-sheets; Nano-particles; CH4 oxidation; Ni2+ defects;

Synthesis, characterization and activity of homogeneous and heterogeneous (SiO2, NaY, MCM-41) iron(III) catalysts on cyclohexane and cyclohexene oxidation by Paula M.A. Machado; Leonardo M. Lube; Marcione D.E. Tiradentes; Christiane Fernandes; Clícia A. Gomes; Alexandre M. Stumbo; Rosane A.S. San Gil; Lorenzo C. Visentin; Dalber R. Sanchez; Vera L.A. Frescura; Jessee S.A. Silva; Adolfo Horn (119-129).
Display OmittedThis work deals with the synthesis and characterization of two homogeneous and three heterogeneous iron(III) catalysts, which were evaluated in the oxidation of cyclohexane and cyclohexene, using H2O2 as oxidant. The homogeneous catalyst [Fe2(BPA)2(μ-OCH3)2(Cl)2], (1), where BPA is the deprotonated form of N-(2-hydroxybenzyl)-N-(pyridin-2-ylmethyl) amine, is a dinuclear iron(III) compound, as determined by X-ray diffraction studies. Compound [FeIII(HBPCℓNOL)(Cl)2], (2), where HBPCℓNOL is N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)(3-chloro)(2-hydroxy) propylamine, is a mononuclear iron(III) compound. The reaction of the ligand HBPA with the 3-glycidoxypropyltrimethoxysilane molecule followed by the reaction with different inorganic matrices (silica-gel, NaY zeolite, MCM-41) resulted in the organo functionalized solids SiL, NaYL and MCM-41L, respectively. These materials were reacted with iron(III) salt, affording the heterogeneous catalysts SiLFe, NaYLFe and MCM-41LFe, respectively. They were characterized by elemental analyses, HR-CS AAS, solid state MAS NMR (29Si, 13C), IR, UV–vis, TGA, Mossbauer, and textural analyses. The major product formed in all the oxidation reactions was the hydroperoxide derivative. When cyclohexane was the substrate, the homogeneous catalysts were more efficient than the heterogeneous ones. In contrast, the heterogeneous systems showed better results with cyclohexene than with cyclohexane, reaching about 30% in the presence of NaYLFe.
Keywords: Cyclohexane oxidation; Cyclohexene oxidation; Grafting; Heterogeneous catalysis; Homogeneous catalysis;

Cobalt-aluminum mixed oxides prepared from layered double hydroxides for the total oxidation of benzene by Dalin Li; Yuanyuan Ding; Xiaofeng Wei; Yihong Xiao; Lilong Jiang (130-138).
Display OmittedA series of Co-Al mixed oxides were prepared by co-precipitation method via Co-Al layered double hydroxides (LDHs) as precursors. The influence of chemical compositions of Co-Al LDHs on the structural and physicochemical properties of Co-Al mixed oxides as well as their catalytic performance for benzene total oxidation was investigated. The samples were characterized by using ICP, N2 physical adsorption, XRD, TG-DTA, SEM, TEM, Raman, H2-TPR, and XPS techniques. The characterization results showed that calcination of Co-Al LDHs gave rise to Co(Co, Al)2O4 spinel-like mixed oxide as the main phase. The crystallite size of Co(Co, Al)2O4 spinel (6 ∼ 19 nm) decreased with decreasing the Co/Al molar ratio, suggesting the inhibition of crystal growth by the incorporation of Al3+ ions in the spinel phase. A drastic change in the state of Co-Al mixed oxide occurred at Co/Al = 6, as indicated by H2-TPR and XPS. In benzene total oxidation, the activity of Co-Al mixed oxide increased with increasing the Co/Al molar ratio, with the highest activity at Co/Al = 5; further increase in the Co/Al molar ratio to 6 led to significant decrease in the activity, properly caused by the change of surface state of mixed oxide. The 50 h long-term stability test revealed that the optimized Co-Al mixed oxide was stable for the total oxidation of benzene.
Keywords: Layered double hydroxides; Cobalt oxide; Mixed oxide; Volatile organic compounds; Catalytic total oxidation;

Au/MnO x /3DOM SiO2: Highly active catalysts for toluene oxidation by Huanggen Yang; Jiguang Deng; Shaohua Xie; Yang Jiang; Hongxing Dai; Chak Tong Au (139-148).
Display OmittedThree-dimensionally ordered macro-/mesoporous silica (3DOM SiO2)-supported manganese oxide and gold nanocatalysts (yAu/zMnO x /3DOM SiO2, y  = 0–0.95 wt%; z  = 2.7–15.4 wt% (weight percentage of Mn2O3)) were prepared using the polymethyl methacrylate-templating, incipient wetness impregnation, and polyvinyl alcohol-protected reduction methods, respectively. It is shown that the yAu/zMnO x /3DOM SiO2 samples displayed a high-quality 3DOM architecture with macropores (180–200 nm in diameter) and mesopores (4–6 nm in diameter) and a surface area of 220–318 m2/g. MnO x nanoparticles (NPs) with a size of 18.7–25.7 nm were dispersed on the surface of 3DOM SiO2, and Au NPs with a size of 3.6–3.8 nm were uniformly dispersed on the surface of zMnO x /3DOM SiO2. The 0.93Au/11.2MnO x /3DOM SiO2 sample performed the best (the temperature required for achieving a 90% toluene conversion was 255 °C at space velocity = 20,000 mL/(g h)) for toluene oxidation. It is concluded that the higher oxygen adspecies concentration, better low-temperature reducibility, and stronger interaction between Au and MnO x NPs as well as the unique bimodal porous structure were responsible for the good catalytic performance of 0.93Au/11.2MnO x /3DOM SiO2.
Keywords: Three-dimensionally ordered macro-/mesoporous; 3DOM SiO2-supported manganese oxide and gold nanoparticle; 3DOM SiO2-supported gold nanoparticle; Toluene oxidation;

Catalytic steam gasification of n-C5 asphaltenes by kaolin-based catalysts in a fixed-bed reactor by Azfar Hassan; Lante Carbognani-Arambarri; Nashaat N. Nassar; Gerardo Vitale; Francisco Lopez-Linares; Pedro Pereira-Almao (149-161).
Display OmittedA possibility of low temperature catalytic steam gasification of n-C5 asphaltenes mixed in light cyclic oil (LCO) in a fixed bed reactor is tested and presented. Four meta kaolin based catalysts containing one alkali (K or Cs), one alkaline earth (Ca or Ba) metal oxides were characterized and tested. Two of these four catalysts also contained NiO nanoparticles in addition to alkali and alkaline earth metal oxides. Addition of sugar as a porogen to kaolin created meso as well as macroporosity. These mesoporous–macroporous meta kaolin based materials are intended to work mainly as catalysts for steam gasification of the adsorbed asphaltenes. XRD data showed presence of Ni3S2 in the spent catalyst. It was found that low temperature catalytic steam gasification was possible by all four catalysts. However, replacement of Ca by Ba increased H2 production. Also, incorporation of NiO nanoparticles promoted further H2 production during the steam gasification of the adsorbed asphaltenes, leading to CO2 and H2 as major products with less side reactions. Of the two nickel-based catalysts, 3NiO6Cs6Ba seems to be the more promising material, with slightly lower activation energy, and higher production of gases per mole of metal contained in the catalyst.
Keywords: n-C5 asphaltenes; Catalytic steam gasification; Kaolin; H2 production; NiO nanoparticles;

Catalytic properties of pure Ni honeycomb catalysts for methane steam reforming by Yusuke Hiramitsu; Masahiko Demura; Ya Xu; Masanari Yoshida; Toshiyuki Hirano (162-168).
Display OmittedHoneycomb catalysts were assembled, using only 30 μm-thick Ni foils, to develop genuine monolithic catalysts for hydrogen production via methane steam reforming. A high cell density (900 cpsi) and geometric surface area (59.4 cm2/cm3) were achieved on the honeycomb catalyst. The catalyst exhibited high CH4 conversion (over 97%) at 1073 K for a long period of up to 8321.1 h under low steam-to-carbon ratio (1.34) and space velocity (335 h−1) conditions. A H2 production rate of 74.2 ml/min was achieved, and carbon deposition was hardly detected in spite of the low steam-to-carbon ratio. The catalyst was gradually deactivated due to the oxidation of Ni, but was repeatedly regenerated by reduction in flowing hydrogen. These findings proved the high potential of the Ni honeycomb catalyst for application to a small-scale hydrogen production system. Monitoring the temperature profile along the axial direction showed good heat transfer between the catalyst and the surrounding gas, which was attributed to the high thermal conductivity of Ni and to the high cell density of the catalyst. The high geometric surface area and good heat transfer are considered responsible for the good performance of the catalyst.
Keywords: Hydrogen production; Metallic honeycomb catalyst; Cell density; Geometric surface area; Temperature profile;