Size-Selective Reactivity of Subnanometer Ag4 and Ag16 Clusters on a TiO2 Surface

Size-selected Ag4 and Ag16 clusters on a titania surface have been studied for their potential in CO oxidation using theoretical calculations and X-ray absorption near edge spectroscopy. The first peak at the measured Ag K-edge of Ag16@TiO2 is more prominent in air than in carbon monoxide environment, but no variation was found between the spectra of Ag4@TiO2 in air and in carbon monoxide environments. Density functional theory calculations show a preference for molecular oxygen adsorption for Ag4@TiO2 and that for a dissociative one on Ag16@TiO2, while carbon monoxide reactions with adsorbed oxygen reduced the Ag16@TiO2 cluster. The dissociated oxygen atoms increased the oxidation state of Ag16 cluster and resulted in the prominent first peak in Ag K-edge spectrum in quasi-particle theory calculations, with the subsequent carbon monoxide oxidation reversing the character of Ag K-edge spectrum associated with the reduction of the cluster. The results provide insight into the size selectivity of supported ...

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