Catalytic Activity of AuCu Clusters on MgO(100): Effect of Alloy Composition for CO Oxidation

Abstract

<p>Density functional simulations have been performed for Au<sub>7</sub>Cu<sub>23</sub> and Au<sub>23</sub>Cu<sub>7</sub> clusters on MgO(100) supports to probe their catalytic activity for CO oxidation. The adsorption of reactants, O<sub>2</sub> and CO, and potential O<sub>2</sub> dissociation have been investigated in detail by tuning the location of vacancies (F-center, V-center) in MgO(100). The total charge on Au<sub>7</sub>Cu<sub>23</sub> and Au<sub>23</sub>Cu<sub>7</sub> is negative on all supports, regardless of the presence of vacancies, but the effect is significantly amplified on the F-center. Au<sub>7</sub>Cu<sub>23</sub>/MgO(100) and Au<sub>23</sub>Cu<sub>7</sub>/MgO(100) with an F-center are the only systems to bind O<sub>2</sub> more strongly than CO. In each case, O<sub>2</sub> can be effectively activated upon adsorption and dissociated to 2 × O atoms. The different reaction paths based on the Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms for CO oxidation have been explored on the Au<sub>7</sub>Cu<sub>23</sub> and Au<sub>23</sub>Cu<sub>7</sub> clusters on F-centers, and the results are compared with the previous findings for Au<sub>15</sub>Cu<sub>15</sub>. Overall, the reaction barriers are small, but the changes in the Au:Cu ratio tune the reactant adsorption energies and sites considerably, showing also varying selectivity for CO and O<sub>2</sub>. The microkinetic model built on the basis of the above results shows a pronounced CO<sub>2</sub> production rate at low temperature for the clusters on F-centers.</p>