DFT Study of Direct Propylene Epoxidation over the Disordered Surface Oxide of Cu₁₂O₆/Cu(111)

Propylene epoxidation reaction is a significant catalytic process utilized in a diverse range of other industrial processes and has been employed for the synthesis of numerous high-value products. Cu-based catalysts have been extensively researched as cost-effective and environmentally friendly catalysts for the epoxidation of propylene. In this paper, Cu12O6/Cu(111) is selected as the precursor of bulk oxidation. Generalized ab initio molecular dynamics (AIMD) simulation shows that Cu12O6/Cu(111) is a highly stable surface oxide under the condition of selective oxidation of propylene. The key competitive reactions of dehydrogenation and epoxidation on the surface of Cu12O6/Cu(111) with lattice oxygen (OL), adsorbed oxygen atoms (O*), and molecular oxygen (O2*) as oxidants have been studied utilizing density functional theory. Due to the high energy barrier of OL as a key step of the oxidizing agent, O* and O2* are mainly used as oxidizing agents in the whole process of the propylene oxidation reaction. The results show that the reaction mechanism of the O2 molecule as an oxidizing agent is better in reactivity and selectivity than that of the O atom as the oxidizing agent. The Cu12O6/Cu(111) surface exhibits a high level of PO selectivity, surpassing the Cu+ selectivity observed on the Cu2O(111) surface and resembling the Cu0 selectivity of the pure metal surface of Cu(111). It is hoped that this study can provide theoretical guidance for designing good catalysts for propylene epoxidation by controlling the oxidation state of copper in the partial oxidation state like surface copper oxide.