Competition of propylene hydrogenation and epoxidation over Au-Pd/TS-1 bimetallic catalysts for gas-phase epoxidation of propylene with O2 and H2

Abstract

Au and Pd play a collaborative effect in the formation of H2O2 from H2 and O2, which is beneficial for the gas-phase epoxidation of propylene over Au-Pd/TS-1 (i.e., Au-Pd bimetallic nanoparticles supported on titanium silicalite-1). However, the introduction of Pd into Au/TS-1 makes this reaction more complicated. In this work, GC–MS results demonstrated the presence of propylene hydrogenation. A small amount of O2 was found to significantly promote the propylene hydrogenation over Au-Pd/TS-1, while O2 concentration had less effect. Four catalysts were designed to discuss the active sites on Au-Pd/TS-1. It was concluded that propylene hydrogenation preferentially occurred at Pd sites and propylene epoxidation occurred at Au-Ti sites. Based on the catalytic performance of Au-Pd/TS-1 at 100 °C, a four-stage model was proposed for the first time to reveal the competition between propylene hydrogenation and epoxidation. Moreover, the addition of CO could abate the propene hydrogenation over Au-Pd/TS-1.