Phosphate-Modified Effects on Uncalcined TS-1-Immobilized Au Catalysts for Propylene Epoxidation with H₂ and O₂

Au nanoparticle sizes, as well as surface properties and Ti species of titanosilicate zeolite, have been identified to significantly influence the performances of Au-Ti bifunctional catalysts over propylene epoxidation with H-2 and O-2 to propylene oxide (HOPO process). Herein, we perform a convenient and efficient strategy to simultaneously regulate the properties of Au and Ti active sites by impregnating phosphate onto the uncalcined TS-1 zeolite (i.e., TS-1-B). The optimal P-modified TS-1-B-immobilized Au catalyst shows notably increased activity by 75% compared to the pristine Au/TS-1-B catalyst with a near PO selectivity and H-2 efficiency. We found that the introduction of phosphate conduces to the Au capture and formation of the smaller-sized Au nanoparticles with the smaller size over the TS-1-B zeolite, which promotes the generation of hydroperoxide species thereon and thus boosts the PO activity. Moreover, the moderate P modification could form highly active Ti species, reduce the surface defect, and enhance the Lewis acid sites over the TS-1-B zeolite, which makes for maintaining acceptable PO selectivity and H-2 efficiency under a high PO formation rate. We suggested this work could help develop efficient modification methods over Au-Ti bifunctional catalysts for this reaction.