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111.
Arnaud Barbier Guy-Antonin Martin Pilar Ramirez de la Piscina Narcis Homs 《Applied Catalysis A: General》2001,210(1-2):75-81
The hydrogenation of carbon monoxide over Co/SiO2 catalysts obtained by reduction of precursors prepared by the reaction of dicobaltoctacarbonyl with silica gives rise to a mixture of alcohols and hydrocarbons. The chain growth probability for hydrocarbon synthesis is similar to that observed over conventional catalysts prepared by the ammonia method (=0.74) with a comparable metal dispersion (metal particle size 4 nm). Alcohol formation yields a smaller chain growth probability (=0.42). Magnetic measurements have shown that in the latter catalyst, small cobalt clusters (1 nm) are likely to be present together with the cobalt particles (4 nm), this observation reconciles apparently conflicting results from the literature. It has been speculated that alcohol formation might be related to the presence of these clusters according to a concerted mechanism. Furthermore, the observation of large amounts of acetates by temperature-programmed hydrogenation, not detected in hydrocarbon selective catalysts, suggests that they may play a role in ethanol synthesis. 相似文献
112.
Pd-Ag thin films were prepared by the RF sputtering method on a Pyrex glass substrate to give monophasic alloys. Oxidation of allylic alcohols using the films gave selectively , -unsaturated carbonyl compounds in the presence of O2; highly dispersed Pd species on Ag, Pd7Ag93 showed 95% selectivity for acrolein from allyl alcohol at 473 K. 相似文献
113.
The hexane-soluble fractions of hydroliquefied products from three Yallourn brown coal lithotypes have been separated into five fractions by combined silica-alumina packed column chromatography. Analyses of various fractions by g.c.-m.s. permitted the identification of ≈50 components in the saturate fraction and 40 components in the diaromatic fraction, together with 30 components in the monoaromatics. The components identified were quite similar among hexane-soluble portions of all three lithotypes. A marked predominance of even carbon number alkane (C23-C29) was observed in the hydrocarbon fractions from pale lithotype over , and medium light lithotype over both pure ZnCl2 and . However, medium dark lithotype over both melt catalysts produced a saturate fraction with an odd carbon number(C22-C28) preference. Based on spectral methods, Soxhlet extracts obtained from untreated lithotypes (hexane and benzene solubles) were characterized as complex mixtures of higher molecular weight(300–1000) aliphatic hydrocarbons, which were supposed to be a precursor of the saturates produced from the corresponding lithotype in the catalytic hydroliquefaction. 相似文献
114.
Patricia Concepción José M. López Nieto Joaquín Pérez-Pariente 《Catalysis Letters》1993,19(4):333-337
VAPO-5 and V/ ALPO-5 catalysts have been tested for the oxidative dehydrogenation of propane. Depending on the vanadium contents and the preparation procedure, different vanadium species and different catalytic behavior are observed. The catalyst containing V5+ species with a tetrahedral coordination presents the higher yield of propene in the oxidative dehydrogenation of propane. The same yields of CO2 are observed on all vanadium aluminophosphate catalysts, while the higher the yield of propene the lower the yield of CO is. 相似文献
115.
Supported molybdenum clusters were prepared by sublimation of Mo(CO)6 onto dehy-droxylated alumina followed by decomposition in flowing dihydrogen at 970 K. These alumina-supported molybdenum clusters were found by XAFS to transform into Mo2C if heated in a 20% methane/H2 mixture at 950 K. For the hydrogenolysis ofn-butane at 510 K and CO-H2 reactions at 570 K, both at atmospheric pressure, molybdenum and carburized molybdenum showed similar, but different for each reaction, turnover rates. The product distribution was the same for each reaction on Mo and Mo2C. In both reactions, in situ XAFS data for fresh and used catalysts indicated that Mo clusters progressively transformed into Mo2C under the reaction conditions 相似文献
116.
Low-loaded vanadia-titania catalysts have been prepared by impregnation of titania P-25 (Degussa). The catalysts were characterized by X-ray diffraction, specific surface area and porosity assessment by nitrogen adsorption at 77 K. For very low vanadia contents the absence of surface acid Brønsted sites leads to dimerization on surface acid Lewis sites, whereas the presence of surface acid Bransted sites when the vanadia content is increased leads to oxidation to carbonyl and carboxylate species. 相似文献
117.
Anton A. Kiss 《Fuel Processing Technology》2011,92(7):1288-1296
Catalytic reactive distillation (RD) offers novel opportunities for manufacturing fatty acid alkyl esters involved in specialty chemicals and at a larger scale in biodiesel. The integration of reaction and separation into one RD unit, corroborated with the use of a heterogeneous catalyst, provides major benefits such as low capital investment and operating costs. This work presents a novel heat-integrated process based on reactive distillation that aims to reduce furthermore the energy requirements for biodiesel production, leading to competitive operating costs. Despite the high degree of integration, the process is well controllable using an efficient control structure proposed in this work. Rigorous simulations embedding experimental results were performed using computer aided process engineering tools, such as AspenTech Aspen Plus and Aspen Dynamics. The RD column was simulated using the rigorous RADFRAC unit with RateSep (rate-based) model, and explicitly considering three phase balances. Steady-state and dynamic simulation results are given for a plant producing 10 ktpy fatty acid methyl esters (FAME) from methanol and waste vegetable oil with high free fatty acids (FFA) content, using sulfated zirconia as green catalyst. The heat-integrated RD process eliminates all conventional catalyst related operations, efficiently uses the raw materials and the reactor volume offering complete conversion of the fatty acids and allowing significant energy savings. Remarkably, compared to previously reported RD processes, the energy requirements of this process are about 45% lower - only 108.8 kW h/ton biodiesel - while the capital investment cost remains the same as no additional equipment is required. 相似文献
118.
119.
How oxide carriers affect the reactivity of V2O5 catalysts in the oxidative dehydrogenation of propane 总被引:1,自引:0,他引:1
The catalytic pattern of several oxide carriers (MgO, Al2O3, ZrO2, TiO2, SiO2, HY zeolite) and supported V2O5 (4.7–5.3 wt%) catalysts in the oxidative dehydrogenation of propane to propylene (PODH) has been comparatively investigated.
The fundamental role of the oxide support on both reducibility and reactivity of vanadia catalysts has been assessed. A direct
relationship between the specific surface activity of oxide carriers and that of vanadia catalysts is discussed. The inverse
relationship between the specific activity and the onset temperature of reduction marks the prevailing redox behaviour of
V2O5 catalysts in the PODH reaction.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
120.
T. Schalow B. Brandt D. E. Starr M. Laurin S. Schauermann Sh. K. Shaikhutdinov J. Libuda H.-J. Freund 《Catalysis Letters》2006,107(3-4):189-196
We have studied the influence of oxygen on the structure and morphology of a Pd/Fe3O4 model catalyst using molecular beam (MB) methods, IR reflection absorption spectroscopy (IRAS) and scanning tunneling microcopy
(STM). The model catalyst was prepared under ultrahigh vacuum (UHV) conditions by physical vapor deposition (PVD) and growth
of Pd nanoparticles on an ordered Fe3O4 thin film on Pt(111).
It is found that surface oxides are formed on the Pd nanoparticles even under mild oxidation conditions (temperatures of 500 K
and effective oxygen partial pressures of around 10−6 mbar). These surface oxides are initially generated at the Pd/Fe3O4 interface and, subsequently, are formed at the Pd/gas interface. The process of formation and reduction of surface and interface
oxides on the Pd particles is fully reversible in that all oxides formed can be fully reduced. As a result, the oxide phase
acts like a storage medium for oxygen during oxidation reactions, as probed via CO oxidation.
The process of surface and interface oxidation is directly connected with the onset of a non-reversible sintering process
of the Pd particles. It is suggested that this sintering process occurs via a mobile Pd oxide species, which is stabilized
by interaction with the Fe3O4 support. The restructuring is monitored via STM and IRAS using CO as a probe molecule. In addition to a decrease in particle
density and Pd surface area, a reshaping of the particles occurs, which is characterized by the formation of well-ordered
crystallites and with a relatively large fraction of (100) facets. After a few oxidation/reduction cycles at 500 K, the sintering
process becomes very slow and the system shows a stable behavior under conditions of CO oxidation. 相似文献