Interplay between Subnanometer Ag and Pt Clusters and Anatase TiO2 (101) Surface: Implications for Catalysis and Photocatalysis

Structural and electronic properties of Agn and Ptn (n = 2, 4, and 8) clusters deposited on anatase TiO2 (101) surface were investigated using density functional theory. Binding mechanisms that characterize deposited subnanometer clusters and the effect of cluster size on the adsorption behavior are explored. The restricted movement of interfacial atoms and interaction of the top layer atom with surface atoms of the support were found to affect the adsorption characteristics. Metal nanoparticle encapsulation by the support is explained via the tendency to maximize orbital overlaps between deposited clusters and surface atoms. The probability of sintering of subnanometer clusters was evaluated using adsorption energy and the number of local minima as indicators, suggesting that sintering is less likely to occur for Ag and Pt clusters larger than trimer and monomer, respectively. The sub-bandgaps introduced by subnanometer clusters are investigated in terms of its formation, size effect, and the correlation with d-band distribution. Absolute values of d-band centers smaller than or close to the bandgap along with smaller standard deviation of d-band lead to the formation of sub-bandgaps, which has implications in photocatalysis.