Computational design of active oxygen sites on AgCu catalysts for selective epoxidation reactions

Ethylene and propylene epoxidation are major industrial processes, worth billions of dollars in the global market. Commercial production traditionally utilizes silver (Ag) or copper (Cu) catalysts; however, these reactions require promoters that are expensive and toxic. Recently, AgCu bimetallic catalysts have gained attention as a potential solution due to copper's oxygen dissociation properties and silver's favorable selectivity. Temperature Programmed Reaction Spectroscopy (TPRS) demonstrates that the nature of the oxygen species on the AgCu surface is crucial to the formation of oxidized ethylene products. Cu(111) surfaces with partial coverages of Ag dosed with oxygen at low temperature and then D₂O at room temperature show promise for selective production of ethylene oxide with minimal production of undesirable acetaldehyde and CO₂. Density-functional theory (DFT) calculations are utilized to investigate the structure and energetics of the active sites for alkene reaction on the AgCu surface, identifying the roles of reactive oxygen, water, and hydroxyl species in promoting epoxidation. Nudged Elastic Band calculations determine chemical pathways, transition states, and activation energy barriers for the epoxidation reaction. Insights from experiment and computation combine to optimize assembly of Ag and oxygen on Cu(111) catalyst surfaces towards the goal of enhancing epoxidation reactivity and selectivity, reducing waste products, and decreasing harmful CO₂ emissions.