Epoxidation of propylene by molecular oxygen over unsupported AgCu x bimetallic catalyst

Abstract

The unsupported Cu and Ag catalysts with different oxidation states were prepared, and their catalytic performances for propylene epoxidation were investigated. The metallic Cu catalyst exhibits much higher catalytic activity and propylene oxide (PO) selectivity than Cu2O and CuO catalysts. The Cu0 species are the main active sites for propylene epoxidation, but Cu2O and CuO species are in favor of CO2 and acrolein production. The PO selectivity of 54.2 % and propylene conversion of 2.6 % can be achieved over the metallic Cu catalyst at 160 °C in initial stage, but metallic Cu catalyst would be oxidized to Cu2O during propylene epoxidation, resulting in a sharp decrease in the PO selectivity and propylene conversion. Nanosize AgCu x bimetallic catalysts were prepared. It is found that adding Ag to the metallic Cu catalysts can prevent the oxidation of Cu and make AgCu x bimetallic catalysts more stable under the condition of propylene epoxidation. The Ag/Cu molar ratio can remarkably affect the catalytic performance of AgCu x catalyst and the selectivity to PO and acrolein. After AgCu x was supported on MO x -modified α-Al2O3, its catalytic performance can be improved and has a close relationship with the acid–base property of support.