enantioselectivehydrogenationofunsaturatedcarboxylicacidseffectsofpalladiumparticlesizeandsupportacidicproperty

Effects of Pd particle size and support acidity on enantioselective hydrogenation of α,β-unsaturated carboxylic acids were systematically studied using Pd nanoparticles with different size immobilized on various oxides. Small Pd particles showed higher activity in the hydrogenation of(E)-2-methyl-2-pentenoic acid due to the larger fraction of edge sites which were more active in olefin hydrogenation; but they did not change the reaction mechanism and/or the adsorption mode of reaction intermediates. Similar correlations in the hydrogenation of(E)-2-methyl-2-butenoic acid and 2-acetamidoacrylic acid further confirmed that the size of Pd particles only mediated the activity but did not alter the enantioselectivity. On the other hand, the activity and the enantioselectivity were strongly dependent on the acidity of the support. The TOF and the ee value followed the order TiO_2 > γ-Al_2O_3 > SiO_2 > CeO_2, suggesting that the acidic support favored the adsorption of the reaction intermediates

enantioselectivehydrogenationofunsaturatedcarboxylicacidseffectsofpalladiumparticlesizeandsupportacidicproperty

Effects of Pd particle size and support acidity on enantioselective hydrogenation of α,β-unsaturated carboxylic acids were systematically studied using Pd nanoparticles with different size immobilized on various oxides. Small Pd particles showed higher activity in the hydrogenation of(E)-2-methyl-2-pentenoic acid due to the larger fraction of edge sites which were more active in olefin hydrogenation; but they did not change the reaction mechanism and/or the adsorption mode of reaction intermediates. Similar correlations in the hydrogenation of(E)-2-methyl-2-butenoic acid and 2-acetamidoacrylic acid further confirmed that the size of Pd particles only mediated the activity but did not alter the enantioselectivity. On the other hand, the activity and the enantioselectivity were strongly dependent on the acidity of the support. The TOF and the ee value followed the order TiO_2 > γ-Al_2O_3 > SiO_2 > CeO_2, suggesting that the acidic support favored the adsorption of the reaction intermediates

Piperazine as a versatile organic structure-directing agent for zeolite synthesis: effect of SiO2/Al2O3 ratio on phase selectivity

The synthesis of aluminosilicate zeolites by using piperazine as the organic structure-directing agent was studied. Under optimized conditions, zeolites ZSM-4 (MAZ), mordenite (MOR), ZSM-35 (FER), ZSM-5 (MFI) and ZSM-12 (MTW) were obtained in pure phase. The effect of SiO2/Al2O3 ratio in the initial gel on zeolite phase selectivity was systematically investigated. The SiO2/Al2O3 ratio ranges for the formation of each zeolite had been established. At low SiO2/Al2O3 ratios, ZSM-4 (SiO2/Al2O3 = 9) and mordenite (SiO2/Al2O3 = 12.8) could be obtained, while ZSM-35 (14.3 <= SiO2/Al2O3 <= 29.3), ZSM-5 (SiO2/Al2O3 = 58.7) and ZSM-12 (SiO2/Al2O3 = 117.2) gradually evolved as the SiO2/Al2O3 ratio increased. Piperazine was considered to have a charge-compensatory role when the amine group was protonated; its overall effectiveness depended on the zeolite structure. Piperazine fitted best with the FER structure, and the obtained FER zeolite had a hierarchical house of card texture which was assembled by the primary plate-shaped crystals. The ZSM-4, mordenite and ZSM-35 zeolites (in acidic form) were tested for the dimethyl ether carbonylation reaction; the essential role of 12-member ring (12MR) pore in mordenite for molecule transportation to the 8MR pore was proved by comparing to ZSM-4 that lacks interconnectivity between 12MR and 8MR pores

Au/ZrO2 catalysts for low-temperature water gas shift reaction: Influence of particle sizes

The size effects of Au and ZrO2 particles on the structural property and the catalytic performance of Au/ZrO2 catalysts for the water gas shift reaction were extensively investigated. It was found that the Au-ZrO2 contact boundaries played essential roles in determining the catalytic reactivity. By keeping the size of Au particle to be similar to 3 nm, the increase in the particle size of ZrO2 from similar to 7 nm to similar to 55 nm caused significant decrease in the reaction rate. When the particle size of ZrO2 was fixed at similar to 20 nm, the conversion of CO decreased greatly with increasing the size of gold particle from 2.9 to 6.2 nm. IR spectroscopy and kinetic study revealed that the water gas shift reaction occurred at the Au-ZrO2 contact boundaries, where CO is adsorbed on the Au species and H2O is activated on the surface of ZrO2 through the formation of formate species, acting as key reaction intermediates

Hydrogen production from ethanol over Ir/CeO2 catalysts: A comparative study of steam reforming, partial oxidation and oxidative steam reforming

Steam reforming, partial oxidation, and oxidative steam reforming of ethanol over Ir/CeO2 catalysts were studied to elucidate the reaction pathway and determine catalytic stability. Temperature-programmed desorption and surface reaction revealed that ethoxy species were immediately formed on ethanol adsorption at room temperature, and were mainly further oxidized to acetate and carbonate species that finally decomposed into CH4/CO and CO2, respectively. Under reaction conditions, acetalclehyde was the primary product below 673 K, which decomposed mainly to methane and carbon monoxide at higher temperatures, whereas methane reforming and the water-gas shift were the major reactions above 773 K. The Ir/CeO2 catalyst demonstrated rather high stability for the reactions at 823 and 923 K with no apparent deactivation for 60 h on stream; the mean size of It particles was stable at around 2-3 nm, but the ceria particles sintered significantly from 6-8 to 14-27 nm. CeO2 likely prevented the highly dispersed It particles from sintering and inhibited coke deposition through strong Ir-CeO2 interactions. (c) 2008 Elsevier Inc. All rights reserved

Dimethyl Ether Carbonylation to Methyl Acetate over Nanosized Mordenites

Nanosized mordenites were found to show significantly enhanced reaction efficiency in dimethyl ether (DME) carbonylation to methyl acetate (MA) because of a greatly facilitated diffusion process. Copper incorporation into the channels of the nanosized mordenites further promoted the reaction rate, selectivity, and stability. Moreover, upon the addition of a small amount of H-2 (5-19 vol %) to the feed gas, deactivation was suppressed during DME carbonylation, whereas the catalyst stability and rate of formation of MA increased

The shape effect of TiO2 in VOx/TiO2 catalysts for selective reduction of NO by NH3

Anatase TiO2 nanosheets exposing 74% of {001} facets and nanospindles exposing 81% of {101} facets were hydrothermally synthesized with the aid of F- and CH3COO-, respectively. Upon vanadia loading at a monolayer amount level, the {001} facets on TiO2 nanosheets favored the deposition of octahedral vanadia species, but the {101} facets on TiO2 nanospindles resulted in the formation of tetrahedral vanadia species. The shape effect of TiO2, in terms of its predominantly exposed crystal facets, on the catalytic performance of VOx/TiO2 samples for selective reduction of NO with NH3 was examined. The octahedral vanadia species on TiO2 nanosheets showed a significantly higher activity than the tetrahedral vanadia species on TiO2 nanospindles

Supported Single Pt₁/Au₁ Atoms for Methanol Steam Reforming

The single Pt₁ and Au₁ atoms stabilized by lattice oxygen on ZnO­{1010} surface for methanol steam reforming is reported. Density functional theory calculations reveal that the catalysis of the single precious metal atoms together with coordinated lattice oxygen stems from its stronger binding toward the intermediates, lowering reaction barriers, changing on the reaction pathway, enhancing greatly the activity. The measured turnover frequency of single Pt₁ sites was more than 1000 times higher than the pristine ZnO. The results provide valuable insights for the catalysis of the atomically dispersed precious metals on oxide supports