Selectivity-Driven Design of the Ag–Cu Alloys for the Ethylene Epoxidation

Recent experiential and theoretical studies have shown that the Ag–Cu bimetallic catalysts possess a high selectivity toward ethylene oxide (EO) in ethylene epoxidation. However, the dependence of selectivity toward EO on Ag–Cu composition remains unclear. In this work, a volcano-like selectivity trend with the increasing surface Cu content (x) of Ag1–xCux/Ag (111) surface alloy has been identified by density functional theory (DFT) calculations. The computational screening demonstrates that the Ag1–xCux/Ag (111) surface alloy would achieve the highest selectivity with around 50% surface Cu composition at 1/9 and 2/9 ML oxygen coverage. We find that the relative bond strength between the C1–O and O–metal bonds in the oxametallacycle (OMC) intermediate would affect the selectivity to EO. Moreover, the transition state, the charge distribution of the Ag–Cu surfaces, and the changes in work function of catalysts upon adsorption of Os are studied, which also to some extent affect the selectivity.