Epoxidation of olefins with oxygen/isobutyraldehyde over transition-metal-substituted phosphomolybdic acid on SBA-15

A series of polyoxometalate-based heterogeneous catalysts were prepared by immobilized transition metal mono-substituted phosphomolybdic acids (PMo11M, M = Fe, Co or Cu) or unsubstituted phosphomolybdic acid (PMo12) on amino-functionalized SBA-15. A variety of characterization results demonstrated that the PMo11M units are uniformly dispersed on the surface or in the channels of mesoporous SBA-15. The catalytic properties of these hybrid materials (denoted as PMo11M/SBA or PMo12/SBA) were investigated in the epoxidation of olefins with molecular oxygen as oxidant and isobutyraldehyde as co-reagent. It has been found that PMo11Co/SBA and PMo11Cu/SBA are catalytically active for the epoxidation of cyclooctene with acetonitrile as solvent, while PMo11Fe/SBA and PMo12/SBA are nearly inactive under the same reaction conditions. Moreover, the relatively active PMo11Co/SBA catalyst could also efficiently convert cyclohexene and 1-octene to the corresponding epoxides, and its catalytic activity was solvent dependent. Using suitable solvent like acetonitrile could efficiently inhibit the deactivation of the catalyst, thus bringing excellent stability and recyclability for the PMo11Co/SBA catalyst. (C) 2015 Elsevier B.V. All rights reserved.