The oxidation of CO at MgO supported gold aggregates is studied by means of density functional theory calculations. In addition to serving as a structural promoter holding the gold particles, the supporting oxide also takes an active role in the bonding and activation of adsorbates bound to the gold. The oxide stabilizes a peroxolike reaction intermediate, $\mathrm{C}\mathrm{O}·{\mathrm{O}}_2$, and causes steric repulsion to CO. The most reactive site at $\mathrm{A}\mathrm{u}/\mathrm{M}\mathrm{g}\mathrm{O}$ appears where the gold shelters the MgO thereby creating a cavity where several low-coordinated Au atoms and ${\mathrm{M}\mathrm{g}}^{2+}$ cations from the substrate can interact simultaneously with an adsorbate.

• Received 29 January 2003

DOI:https://doi.org/10.1103/PhysRevLett.90.206102