(81e) Poisoning Mechanisms of MgO-Supported Au Clusters in CO Oxidation

We investigated the CO oxidation mechanism on MgO-supported, subnanometer Au catalysts (Au₆, Au₈ and Au₁₀), through multiscale modeling that combines density functional theory calculations with kinetic Monte Carlo simulations. For the case of Au₆, our work unravels multiple catalyst deactivation mechanisms that depend on the type of the support vacancies. In defect-poor MgO or in the presence of a Mg-vacancy, O₂ interacts weakly with Au₆ and poisoning occurs by CO. On Au₆ clusters that interact with an O vacancy of the support, O₂ can be chemisorbed and some activity is observed. However, eventually, the Au₆ cluster is poisoned by carbonate. For the similar case of negatively charged Au₈ and Au₁₀ clusters the carbonate formed was shown to decompose through pathways that result in CO₂ production. Thus, these three different clusters were shown to exhibit different activity towards the CO oxidation reaction. This study underscores the importance of a cluster’s charge state on the catalytic activity and explains several experimental observations regarding the variable activity of metal-oxide supported Au nanoclusters.