Catalytic property of hetero-elements isolated in crystalline mesoporous transition metal oxides

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The evaluation of characteristic features of hetero-atoms embedded in crystallized mesoporous transition metal oxides are aimed in the present research. At the beginning as references, the catalytic performance of non-doped pure mesoporous transition metal oxides was evaluated by oxidation of olefins with hydrogen peroxide. Mesoporous tantalum oxide was found to be an efficient catalyst for oxidation of cyclohexene in cetonitrile solvent, whose activity exceeded the one expected from the surface area in comparison with non-porous materials. Ti doping to the mesoporous Ta oxide was also attempted, but no improvement was observed due to the high activity of the other material itself. In the term 2007, mesoporous Nb oxide was studied in detail.The oxidation of cyclohexene with hydrogen peroxide resulted in over 80 % selectivity for cyclohexanediol over amorphous mesoporous Nb oxide, while a similarly high selectivity was observed for epoxycyclohexane over crystalline mesporous Nb oxide. These results indicate that the selectivity of catalytic reactions can be controlled by changing the crystal structure of mesoporous transition metal oxides. By optimizing the reaction conditions, 12 % of conversion of the reactant ant 97 % of selectivity for epoxycyclohexane were obtained by the oxidation of cyclohexene with hydrogen peroxide over crystalline mesoporous Nb oxide even at 40 ℃ for 2 h.While Ti-containing zeolites are commercially utilized for the epoxidation of linear olefins, they are not effectively catalyze larger-sized molecules than zeolitic pores represented by cyclohexe. In this point of view, the present finding that mesoporous transition metal oxides can function the epoxidation of larger olefins, especially the crystalline mesoporous Nb oxide, would contribute to the practical development of catalytic systems in addition to the academic importance.