Catalytic steam reforming of ethanol to produce hydrogen and acetone

Steam reforming of ethanol over CuO/CeO2 was studied. Acetaldehyde and hydrogen were mainly produced at 260degreesC. At 380degreesC, acetone was the main product, and 2 mol of hydrogen was produced from 1 mol of ethanol. The formation of hydrogen accompanied by the production of acetone was considered to proceed through the following, consecutive reactions: dehydrogenation of ethanol to acetaldehyde. aldol condensation of the acetaldehyde, and the reaction of the aldol with the lattice oxygen [O(s)] on the catalyst to form a surface intermediate, followed by its dehydrogenation and decarboxylation. The overall reaction was expressed by2C(2)H(5)OH + H2O --> CH3COCH3 + CO2 + 4H(2). Ceria played an important role as an oxygen supplier. The addition of MgO to CuO/CeO2 resulted in the production of hydrogen at lower temperatures by accelerating aldol condensation. (C) 2004 Elsevier B.V. All rights reserved.

Catalytic oxidation of cyclohexane to cyclohexanol and cyclohexanone over Co3O4 nanocrystals with molecular oxygen

Co3O4 nanocrystals with average particle sizes of 30 and 50 run were synthesized using cobalt nitrate as precursor, and were characterized by X-ray diffraction (XRD), nitrogen adsorption, transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. Catalytic oxidation of cyclohexane with molecular oxygen was studied over Co3O4 nanocrystals. These catalysts showed obviously higher activities as compared to Co3O4 prepared by the conventional methods, Co3O4/Al2O3, or homogeneous cobalt catalyst under comparable reaction conditions. The 89.1% selectivity to cyclohexanol and cyclohexanone at 7.6% conversion of cyclohexane was realized over 50 nm sized Co3O4 nanocrystals at 393 K for 6 h. (c) 2005 Elsevier B.V. All rights reserved.

Synthesis of FeCoMnAPO-5 molecular sieve and catalytic activity in cyclohexane oxidation by oxygen

A new FeCoMnAPO-5 with AFI structure was synthesized under hydrothermal conditions and characterized by XRD, FT-IR, X-ray fluorescence, nitrogen adsorption and SEM. The oxidation of cyclohexane with molecular oxygen was studied over the catalyst at 403 K. It show d higher activity compared to FeAPO-5, CoAPO-5 and MnAPO-5. The FeCoMnAPO-5 catalyst was recycled twice without loss of activity or selectivity.

Production of light olefins and aromatic hydrocarbons through catalytic cracking of naphtha at lowered temperature

Naphtha catalytic cracking were carried out at 650 degrees C over modified ZSM-5. Light olefins and BTX could be obtained over the catalysts. The products showed variable distribution with different catalyst modification. Some modification, such as Fe, Cu and La favored the BTX generation and P and Mg modification favored the light olefins production. In N-2 stream cracking catalyzed by LaZSM-5, more than 50% naphtha feed were converted to BTX, while in steam cracking, with an improved modified catalyst, P, La/ZSM-5, naphtha can be converted to light olefins with high activity and long-term stability.

Gas phase catalytic partial oxidation of toluene in a microchannel reactor

Gas phase partial oxidation of toluene over V/Ti oxide catalysts has been successfully performed in a microchannel reactor, which provides very good mass and heat transfer conditions. With the elimination of hot spots, which are known as the most negative factors for partial oxidation of hydrocarbons, steady and uniform reaction conditions can be achieved in the catalyst bed by using, the microreactor. Since the best performance of the catalysts might be exploited, the selectivity of partial oxidation products of toluene has remarkably increased compared to the traditional packed fixed-bed reactor, even without the bother of modifying the catalysts, diluting the reactants or catalysts with inert contents to avoid hot spots or improve the diffusion and mixing. Furthermore, in virtue of its inherent safety features, when using pure oxygen as oxidant, the reactions were handled safety within the explosion limits in the microreactor. With TiO2 carried V2O5 as catalysts, the total selectivity of benzaldehyde and benzoic acid reaches around 60%, and the toluene conversion is about 10%. The conversion can go up without violent decline of selectivity, unlike most fixed bed reactors. Space time yield of 3.12 kg h(-1) L-1 calculated on the basis of the channel volume has been achieved. The influence of operating conditions has been investigated in detail in the microreactor. (c) 2005 Elsevier B.V. All rights reserved.

Enhancement of the catalytic performance of supported-metal catalysts by pretreatment of the support

We report an interesting finding that the catalytic performance of supported Ag/SiO2 catalysts toward selective catalytic oxidation of CO in hydrogen at low temperatures can be greatly enhanced by pretreatment of the SiO2 support before catalyst preparation. Calcination of SiO2 at appropriate temperatures preferentially removes the H-bonded SiOH, which results in the highly dispersive Ag/SiO2 catalyst and thus improves the catalytic performance. (c) 2005 Elsevier Inc. All rights reserved.

The effect of Rh particle size on the catalytic performance of porous silica supported rhodium catalysts for CO hydrogenation

Silica-supported Rh catalysts with different Rh particle dimensions were investigated for CO hydrogenation. The catalysts were characterized by various techniques such as TEM, H-2-TPR and N-2 adsorption to study the catalyst morphology, the size distributions of Rh particles and the silica pores. It was found that the distribution and the size of Rh particles were affected by the silica pores, and the metal grains were enclosed in the pores of the support, and thereby their growth was limited. The catalytic activity and selectivity to C-2-oxygenates for CO hydrogenation were found to be significantly controlled by the Rh particle sizes, and the higher activity and selectivity to C2-oxygenates were obtained over bigger Rh particles, within the range of the reported particle sizes.

On the correlation between microstructural changes of Ag-H-ZSM-5 catalysts and their catalytic performances in the selective catalytic reduction of NOx by methane

The silver catalyzed, selective catalytic reduction (SCR) of nitrogen oxides (NOx) by CH4, is shown to be a structure-sensitive reaction. Pretreatment has a great affect on the catalytic performances. Upon thermal treatment in inert gas stream, thermal induced changes in silver morphology lead to the formation of reduced silver species of clusters and particles. Catalysis over this catalyst indicates an initially higher activity but lower selectivity for the CH4-SCR of NOx Reaction induced restructuring of silver results in the formation of ill-defined silver oxides. This, in turn, impacts the adsorption properties and diffusivity of oxygen over silver catalyst, results in the decrease in activity but increase in selectivity of Ag-H-ZSM-5 catalyst for the CH4-SCR of NO.. (c) 2004 Elsevier B.V. All rights reserved.

Synthesis and catalytic reactivity of MCM-22/ZSM-35 composites for olefin aromatization

A series of MCM-22/ZSM-35 composites has been hydrothermally synthesized and characterized by XRD, SEM, particle size distribution analysis, N-2 adsorption and NH3-TPD techniques. Pulse and continuous flow reactions were carried out to evaluate the catalytic performances of these composites in aromatization of olefins, respectively. It was found that MCM-22/ZSM-35 composites could be rapidly crystallized at 174 degrees C with an optimal gel composition of SiO2/Al2O3=25, Na2O/SiO2=0.11, HMI/SiO2=0.35, and H2O/SiO2=45 (molar ratio), of which the weight ratio of ZSM-35 zeolite in the composite relied on the crystallization time. The coexistence of MCM-22 and ZSM-35 in the composite (MCM-22/ZSM-35=45/55 wt/wt) was observed to exert a notable synergistic effect on the aromatization ability for butene conversion and FCC gasoline updating, possibly due to the intergrowth of some MCM-22 and ZSM-35 layers.

Factors influencing the catalytic activity of SBA-15-supported copper nanoparticles in CO oxidation

Copper nanoparticles were deposited onto mesoporous SBA-15 support via two different routes: post-grafting method and incipient wet impregnation method. Both XRD and TEM reveal that the post-grafting can make Cu particles very small in size and highly dispersed into channels of SBA-15, while the impregnation method mainly forms large Cu particles on the external surface of SBA-15. TPR experiments show that CuO species formed by the post-grafting method is more reducible than that prepared by the impregnation method. The catalytic activity tests for CO oxidation manifests that the sample prepared by the post-grafting method has a much higher activity than that prepared by the impregnation method, with a lowering of 50 degrees C for T-50, showing a strong dependence of catalytic activity on the size and dispersion of Cu particles. Besides the preparation procedure, other factors including calcination temperature, reduction treatment, copper loading as well as the feed composition, have an important effect on the catalytic activity. The best performance was obtained when the catalyst was calcined at 500 degrees C and reduced at 550 degrees C. The calcination and reduction treatment at high temperature have been found to be necessary to completely remove the organic residue and to generate active metallic copper particles. (c) 2005 Elsevier B.V. All rights reserved.