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.