(560dl) An Interesting Four-Stage Model of Au-Pd/TS-1 Bimetallic Catalysts for Direct Propylene Epoxidation with H2 and O2

Au-Pd bimetallic nanoparticles (NPs) has been proven to be active for the direct synthesis of hydrogen peroxide (H₂O₂), which has attracted significant research interest. In this study, supported Au-Pd NPs on titanium silicalite-1 (denoted as Au-Pd/TS-1), prepared by the alcohol reduction method, shows activity for direct propylene epoxidation with H₂ and O₂. Generally speaking, the propylene epoxidation reaction is performed at 200 °C over Au/TS-1. But for Au-Pd/TS-1, when the reaction was carried out at 100 °C, the catalytic performance exhibited an interesting phenomenon. It can be divided into four stages, denoted as stages I, II, III and IV. In the stage I, propylene hydrogenation dominants and then the epoxidation dominants in the stage II. Afterwards, the two reactions achieve a balance in the stage III and the activity decreases gradually in the stage IV. Based on these, we propose an interesting four-stage model for the first time. The insights reported here reveal the competition between hydrogenation and epoxidation reactions of propylene, as well as may guide us to understand the reaction mechanism of propylene epoxidation over Au-Pd/TS-1 bimetallic catalysts.