Development of liquid-phase oxidation processes by use of highly dispersed metal-metal oxide catalysts

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We aimed at developing new catalyst systems which promote the partical oxidation of hydrocarbons. In the liquid phase conditions we have found that the size of the zeolite TS-1 crystals have a great influence on the activity of the catalyst because of the diffusion limitation of the reactants/products. The V-containing catalyst VS-2 was synthesized and proved to be active in the oxidation terminal carbons as well as internal carbons. By spin trapping experiments the formation of alkyl radical was detected for the alkane oxidation systems catalyzed by VS-2. The utilization of oxygen instead of H_2O_2 was attained by introducing metallic components incorporated inside the metallosilicates ; the catalyst seems to act as a bifunctional system. However, the rate of oxidation decreased with increasing temperature up to > 50ﾟC because of the promotion of the hydeogenolysis of H_2O_2. We have been successful in extending the system to gas phase oxidation. Methane was oxidized to formaldehyde over Pd/TS-1 in the presence of H_2 and O_2. Without addition of H_2 the complete oxidation occurred to give CO_2. Similar formaldehyde synthesis was also carried out over the mesoporous catalysts containing transition metals. Hydrothermally synthesized Mo-containing MCM-41 was found most selective for formaldehyde formation from methance and O_2. Vanadium-containing MCM-41 was active in the deep oxidation of methane. It is to be noted that the hydrothermally synthesized mesoporous metallosilicates were more selective than the mesoporous silicates impregnated with metal salts. The selectivity for formaldehyde was sharply dependent on the pore size of the zeolites/molecular sieves, which was interpreted in terms of the successive decomposition of once formed formaldehyde inside the relatively small pores.