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 H(2)O and 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 CO2 occurs with a small activation barrier of approximately 0.5 eV. A complete catalytic cycle of the water-enhanced CO oxidation is discussed.