A Ti-substituted polyoxometalate as a heterogeneous catalyst for olefinepoxidation with aqueous hydrogen peroxide

Abstract

The Ti-substituted polyoxometalates ([C₁₂mim]₅PTiW₁₁O₄₀, [CTA]₅PTiW₁₁O₄₀ and [TBA]₅PTiW₁₁O₄₀) were prepared and characterized by FT-IR, NMR, UV-vis and ICP-AES. Then the polyoxometalates (POM) were used as catalysts for the epoxidation of various olefins. It was found that the organic countercations had a considerable effect on the catalytic performance. In addition, UV-vis and the FT-IR spectroscopy indicated that the peroxo structure regarded as the active site for oxygen transfer was present even after the reaction, which led to the increasing reaction rate in the second run due to the disappearance of the induction period, as compared with that in the first run. A heterogeneous reaction mechanism has been suggested in olefin epoxidation catalyzed by a Ti-substituted polyoxometalate ([C₁₂mim]₅PTiW₁₁O₄₀) with aqueous hydrogen peroxide in ethyl acetate. The heterogeneous POM catalyst can be easily separated and recycled eight times without decreasing the catalytic activities.