The construction of Mo6−δO3−x-supported catalyst for low-temperature propylene gas-phase epoxidation by Cu modification

Abstract

Selective epoxidation of propylene by molecular oxygen under mild conditions remains a great challenge to date. Here, we successfully designed and constructed molybdenum oxide in an electron-rich state by introducing the transition metal copper into MoO3–Bi2SiO5/SiO2 through a simple co-impregnation method. The new Mo species has the structure Mo6−δO3−x, and greatly improved propylene epoxidation performance at low temperatures. Propylene oxide formation rate increased from 106 to 336 g PO kgcat−1 h−1. X-ray photoelectron spectrometry (XPS) and UV–visible diffuse reflection (UV–vis DRS) characterizations suggest that the bridging oxygen bond between molybdenum and copper produces an oxygen vacancy, which facilitates the formation of the electron-rich state of molybdenum with lower 3d electronic binding energy. In addition, the incorporation of Cu effectively inhibits the formation of Bi2Mo3O12 and improves the dispersion of Mo species. Furthermore, kinetic studies show that Cu-modified catalysts maintain lower apparent activation energy for propylene epoxidation, which obviously reduced the selectivity of acrolein and then conspicuously improved the selectivity of propylene oxide. Our results not only offer a new solution for low temperature propylene epoxidation, but also provide a new strategy for the design of other types of low-temperature epoxidation catalysts.