Theoretical investigation on CO oxidation catalyzed by a copper nanocluster

Abstract

The mechanism of CO oxidation catalyzed by a 55-atom copper nanocluster was studied at the BVP86/DNP level with all-electron scalar relativity. Eley–Rideal (ER) and Langmuir–Hinshelwood (LH) mechanisms were studied in detail. Adsorption of O₂ on the copper cluster was prior to that of CO. The ER mechanism included three pathways, i.e. the O₂ dissociation, the O abstract from the O₂-pre-adsorbed Cu₅₅ cluster by the gaseous CO, and the insertion of CO into the O–O bond of the O₂-precovered Cu₅₅ cluster to form a carbonate-like intermediate to complete the CO oxidation. The LH mechanism was originated from the co-adsorption of CO and O₂ on the Cu₅₅ cluster and had three pathways to the final product. The reaction channels involving the O₂ dissociation, the O-abstraction, and the insertion of CO into the O–O bond vied with each other. The commonly accepted LH mechanism via the peroxo-like intermediate was unfeasible because of the unstable co-adsorption of CO and O₂ on the Cu₅₅ cluster. After incorporating the entropy effect, the CO-assisted O₂ dissociation pathway was the most feasible reaction channel above 250 K. The strong interaction of oxygen atom with the copper surface was in favour of the O₂ dissociation step, and was adverse to the reaction of the atomic oxygen toward CO to form CO₂.