Water-Enhanced Catalysis of CO Oxidation on Free and Supported Gold Nanoclusters

The enhancement by water molecules of the catalytic activity of gas-phase and supported gold nanoclusters toward CO oxidation is investigated with first-principles calculations. Coadsorption of ${\mathrm{H}}_{2}\mathrm{O}$ and ${\mathrm{O}}_{2}$ leads to formation of a complex well bound to the gold cluster, even on a defect-free MgO(100) support. Formation of the complex involves partial proton sharing between the adsorbates, that in certain configurations results in proton transfer leading to the appearance of a hydroperoxyl-like complex. The O-O bond is activated, leading to a weakened peroxo or superoxolike state, and consequently the reaction with CO to form ${\mathrm{CO}}_{2}$ occurs with a small activation barrier of $\ensuremath{\sim}0.5\text{ }\text{ }\mathrm{eV}$. A complete catalytic cycle of the water-enhanced CO oxidation is discussed.