Mechanistic study of CO oxidation by N2O over Ag7Au6 cluster investigated by DFT methods

The potential of Ag7Au6 alloy nanocluster to be a catalyst for the oxidation of CO by N2O has been examined by density functional theory calculations. In the first mechanistic step, an N2O molecule decomposes at the Ag facet site of the Ag7Au6 cluster, yielding an N-2 molecule and an Ag7Au6-O intermediate. In the second step, the Ag7Au6-O intermediate readily reacts with CO to form CO2. The product CO2 desorbs easily from the active Ag7Au6 site, thus avoiding catalyst poisoning. The potential energy surfaces of the doublet- and quartet-states have been systematically elucidated. There is no spin crossing found for the entire reaction and the results show that the reaction preferably follows the doublet state pathway. The activation Gibbs free energy barrier for the first and second steps are 24.6 and 10.6 kcal/mol, respectively, while the Gibbs free energy of the overall reaction is -81.2 kcal/mol. The results reveal that this catalyzed reaction is both thermodynamically and kinetically favorable. Therefore, the Ag7Au6 nanocluster is predicted to be a promising and highly active catalyst for conversion of CO and N2O pollutants to non-harmful products under ambient conditions. (C) 2017 Elsevier B.V. All rights reserved.