Phenyl Ring Transfer Mechanism of Styrene Selective Oxidation to Phenyl Acetaldehyde on Gold Catalysts from Density Functional Theory (DFT) Studies

Olefin selective oxidation is one of the most important reactions in the modern chemical industry. In this work, we systematically studied the reaction mechanism of styrene selective oxidation to benzaldehyde, styrene epoxide, and phenyl acetaldehyde on various model 0 atom preadsorbed gas-phase gold clusters Au-N(q) (N = 16, 28, 34, 55; q = 0, +/- 1) and flat Au(111) surfaces by means of density functional theory (DFT) calculations. We proposed a new reaction channel, namely, the styrene first interacts with the oxygen-adsorbed gold catalysts to form a five-membered ring known as oxametallacycle intermediate (OMME), and then the phenyl group linked to the alpha-C atom transfers to the beta-C atom and forms phenyl acetaldehyde. This new mechanism is different from the hydrogen atom transfer mechanism proposed previously. The DFT calculation results showed that the new reaction pathway for the formation of phenyl acetaldehyde is energetically feasible over the gold clusters as well as the Au(111) surface and exhibits high selectivity on the positively charged and neutral gold clusters, whereas on the anionic gold clusters, it has no outstanding selectivity. This work provided new mechanistic insights into the styrene selective oxidation and the effect of charge state of gold clusters.