Theoretical investigation on CO oxidation catalyzed by a copper nanocluster

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 O-2 on the copper cluster was prior to that of CO. The ER mechanism included three pathways, i.e. the O-2 dissociation, the O abstract from the O-2-pre-adsorbed Cu-55 cluster by the gaseous CO, and the insertion of CO into the O-O bond of the O-2-precovered Cu-55 cluster to form a carbonate-like intermediate to complete the CO oxidation. The LH mechanism was originated from the co-adsorption of CO and O-2 on the Cu-55 cluster and had three pathways to the final product. The reaction channels involving the O-2 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 O-2 on the Cu-55 cluster. After incorporating the entropy effect, the CO-assisted O-2 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 O-2 dissociation step, and was adverse to the reaction of the atomic oxygen toward CO to form CO2.