Epoxidation of propylene with molecular oxygen in methanol over a peroxo-heteropoly compound immobilized on palladium exchanged HMS

Abstract

The peroxo-heteropoly compound {HPO₄[W(O)(O₂)₂]₂} was synthesized on the surface of HMS by reacting HMS-PrNH(PO₃H₂) with [W₂O₃(O₂)₄(H₂O)₂]²⁻ solution, and then palladium ions were exchanged into the channels of HMS to form a hybrid catalyst. The novel solid catalyst showed 34.1% propylene conversion and 83.2% selectivity for propylene oxide for the oxidation of propylene using molecular oxygen as an oxidant in methanol at 373 K for 6 h. Because {HPO₄[W(O)(O₂)₂]₂} was immobilized on the HMS surface by chemical bonds and palladium particles formed during the reaction were fixed in the HMS channels, the solid catalyst could be reused by a simple filtration method and the active components did not leach into the methanol medium after reaction. The selectivity for propylene oxide over the solid catalyst was similar to that over a homogeneous catalyst containing [(C₆H₁₃)₄N]₂{HPO₄[W(O)(O₂)₂]₂} and Pd(OAc)₂, but the propylene conversion over the solid catalyst was lower than that over the homogeneous catalyst. The highest yield of propylene oxide obtained over the solid catalyst by increasing catalyst amount was similar to the highest yield of propylene oxide over the homogeneous catalyst.