Nature of Ag Islands and Nanoparticles on the CeO2(111) Surface

Ag nanoparticles have been deposited on stoichiometric and or reduced thin CeO2 films grown on Pt(111). The nucleation and growth of the Ag nanoparticles has been characterized by STM and XPS (X-ray photoemission spectroscopy) measurements complemented with DFT calculations on Ag atoms, clusters, and extended layers deposited on slab models of the CeO2(111) surface. The XPS spectra clearly show a reduction of the ceria support by Ag deposition (formation of Ce3+ ions). This is accompanied by a positive shift of the Ag 3d core levels, in which final state effects related to the finite size of the Ag deposits come into play. The DFT calculations support the view of a direct electron transfer from the Ag clusters and nanoparticles to the ceria support. Other possible origins of the reduction of the ceria substrate, like the occurrence of oxygen reverse spillover on the Ag nanoparticles, are ruled out based on energy considerations.