Confirmation of Gold Active Sites on Titanium-Silicalite-1-Supported Nano-Gold Catalysts for Gas-Phase Epoxidation of Propylene

The nature of gold active sites on Au–Ti catalysts dictates the reactivity and selectivity during propylene epoxidation reactions. The type of the sites and the location of Au clusters on the external surfaces of TS-1 or inside the TS-1 nanopores have remained the topic of interest. We synthesized and characterized dispersed Au clusters on titanium silicate-1 (Au/TS-1), uncalcined TS-1 (Au/un TS-1), and TS-1 coated with silicalite-1 (Au/S-1/TS-1) to probe the nature of gold active sites for gas-phase epoxidation of propylene. The results of Au/TS-1 and Au/S-1/TS-1 show the importance of Au nanoclusters (<1.0 nm) inside TS-1 nanopores. Propylene oxide (PO) rate of Au/un TS-1 suggests Au nanoclusters (<1.0 nm) on the external surfaces also play an important role. On the basis of this conclusion, better performance for direct propylene epoxidation can be developed over Au–Ti catalysts with Au nanoclusters (<1.0 nm) either inside TS-1 nanopores or on the external surfaces.