Mechanistic Insights into Propene Epoxidation with O₂–H₂O Mixture on Au₇/α-Al₂O₃: A Hydroproxyl Pathway from ab Initio Molecular Dynamics Simulations

We have studied the mechanism of propene epoxidation with O₂–H₂O mixture on Au₇/α-Al₂O₃(0001) using global minimum approach, density functional theory (DFT), and ab initio molecular dynamics (AIMD) methods. It is found that water can easily dissociate on coordinatively unsaturated surface Al sites to form a hydroxylated Al₂O₃ surface. The Au₇ cluster on such a surface prefers anchoring at bare Al sites and transfers from upright to flat structures with a decrease of surface hydroxyl groups. The activation of molecular oxygen via a hydroperoxyl (OOH) intermediate (i.e., O₂ abstracting a hydrogen atom from coadsorbed water) is identified to be a feasible pathway from both AIMD simulations and static DFT calculations. Additional water promotes the H-transfer process by constructing a hydrogen-bonding chain with reactants. The resulting OOH turns out to be a key oxidative species for subsequent propene epoxidation. It can either dissociate into atomically oxygen species to epoxide propene or combine with propene directly, forming an important *C₃H₆OOH species that could be easily transformed to epoxypropane. This study reveals the important role of water in propene epoxidation and may stimulate further exploration and the usage of O₂–H₂O mixture as oxidizing agent in other oxidation reactions