Kinetics and mechanistic insights into the active sites of Au catalysts for selective propylene oxidation

Identification of the catalytically active sites emerges as the prerequisite for an atomic-level comprehensive understanding and further rational design of highly efficient catalysts. Here, we demonstrate a kinetics strategy to identify the active sites of Au catalyst for the disentanglement of geometric and electronic effects on the selective oxidation of propylene to acrolein. Both the Ti-containing titanium-silicalite-1 (TS-1) and Ti-free silicalite-1 (S-1) were employed as supports to immobilize Au catalysts, which were investigated by a combination of multiple characterization, kinetics analysis, and crystal structure modelling. The Au (111) sites are identified as the main active site for acrolein formation, while their electronic effects are highly relevant to the presence or absence of Ti. Moreover, propylene epoxide (PO) formation mainly involves the co-participation of Au and Ti sites, and the proximity between Au and Ti sites is found to have less influences on PO formation in a certain distance. In comparison, acrolein is very likely to generate over Au (111) sites via the hydrogen-assisted O₂ activation to oxygenated species for its oxidizing propylene. The insights gained here could guide the design and preparation of Au catalysts for selective propylene oxidation.