Selective oxidation of propane to acetone (AC) with H₂ and O₂ provides a direct route to convert low-cost propane into value-added products. Unfortunately, the catalytic activity of conventional Au/Ti-based catalysts is constrained by the high energy barrier for H₂ dissociation. Herein, uncalcined TS-1 supported Au-Pd bimetallic catalysts were prepared, the relationship between the active-site structure and corresponding performance in the selective oxidation of propane with H₂ and O₂ in the gas phase was systematically investigated. In contrast to the liquid-phase reaction, trace Pd alloyed with Au triggered an increase in both catalytic activity and selectivity, in which Au₂₀-Pd₁/TS-1-B catalyst exhibited excellent activity (170 g_AC·h^-1·kg_cat^-1) and AC selectivity (90.6%), much higher than those of the Au/TS-1-B catalyst (AC formation rate of 100 g_AC·h^-1·kg_cat^-1 and AC selectivity of 86.3%). It was found that Pd was gradually isolated into monomers with the increase of Au/Pd molar ratio, the synergy between Pd single atoms and Au improved the catalytic performance via enhancing hydrogen dissociation and modulating the electronic structure of Au. Furthermore, the reaction conditions were optimized based on the kinetics studies and the Au₂₀-Pd₁/TS-1-B catalyst exhibited enhanced H₂ selectivity (45%) and long-term stability (over 130 h). The insights gained here can offer valuable guidance for the design of Au-Pd catalysts applicable to other gas-phase oxidation reactions.

Propylene epoxidation by H₂ and O₂ to propylene oxide (PO) over the Au-Ti bifunctional catalysts, as an ideal reaction for PO production, has attracted great interest. Revealing the mechanism of acrolein formation is of great importance for understanding the mechanism of molecular oxygen activation and the formation of hydroperoxo species on the Au sites. Here, we investigate the reaction mechanism of propylene oxidation to acrolein on the Au/uncalcined TS-1 (Au/TS-1-B) catalyst through a combination of multiple characterization, H₂/D₂ exchange, kinetics experiment, and modeling. The Ti sites are found to be non-essential to acrolein formation. Moreover, the acrolein formation on the Au/TS-1-B catalyst is confirmed to be promoted by H₂ through hydroperoxo species formation, which includes two main steps: propylene dehydrogenation to *C₃H₅ with the aid of *OOH species, and *C₃H₅ oxidation by *OOH to acrolein. The latter step is determined to be the rate-determining step because the corresponding kinetics model gives the best description for experimental results. This work not only provides kinetics insights for the propylene hydro-oxidation to acrolein on the Au-Ti bifunctional catalysts, but also facilitates the rational design of Au catalysts with high activity and selectivity in the direct propylene epoxidation with H₂ and O₂.

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.