Cu(I)-Catalyzed Epoxidation of Propylene by Molecular Oxygen

We found that a simple K+-modified CuOx−SiO2 catalyst prepared by a sol−gel method was efficient for the epoxidation of propylene by oxygen. The catalyst did not require prereduction, and propylene oxide (PO) could be formed with a selectivity of 78% under oxygen-rich conditions. We demonstrated that Cu(I) formed during the reaction over the K+-modified CuOx−SiO2 catalyst was the active site for propylene epoxidation by oxygen. Cu(I) was proposed to account for the activation of oxygen, generating an active oxygen species for propylene epoxidation, while K+enhanced the PO selectivity probably by neutralizing the Lewis acid sites on catalyst surface. The enhanced dispersion of copper species due to the interaction with K+ may also contribute to the increase in PO selectivity.