Copper-based efficient catalysts for propylene epoxidation by molecular oxygen

Among a series of SBA-15-supported transition metal oxides with and without modification, the CuOx/SBA-15 after K+ modification exhibited the best catalytic performance for the epoxidation of propylene by molecular oxygen. Potassium was the best modifier among various alkali and alkaline earth metal ions examined, and potassium acetate was a superior precursor of K+ for propylene oxide formation. The highest propylene oxide selectivity was obtained over a catalyst with copper content of 1 wt.% and K/Cu molar ratio of 0.7. Kinetic studies reveal that the allylic oxidation mainly proceeds over the CuOx/SBA-15 providing acrolein as the main partial oxidation product, and the K+ modification switches the main reaction route from allylic oxidation to epoxidation. The characterizations suggest that copper species with content of ≤5 wt.% are located in the mesoporous channels of SBA-15 existing mainly as CuOx clusters and Cu2+ ions, and there exists an interaction between K+ and the copper species. This interaction is proposed to play pivotal roles in epoxidation of propylene. As compared with other reported Cu-based catalysts for propylene epoxidation, the present catalyst possesses several distinct features.