Sn interaction with the CeO2(1 1 1) system: Bimetallic bonding and ceria reduction

A tin layer 0.8 nm thick was deposited onto the CeO2(1 1 1) surface by molecular beam deposition at a temperature of 520 K. The interaction of tin with cerium oxide (ceria) was investigated by X-ray photoelectron spectroscopy (XPS), ultra-violet photoelectron spectroscopy (UPS) and resonant photoelectron spectroscopy (RPES). The strong tin–ceria interaction led to the formation of a homogeneous bulk Ce–Sn–O mixed oxide system. The bulk compound formation is accompanied by partial Ce4+ → Ce3+ reduction, observed as a giant 4f resonance enhancement of the Ce3+ species. CeO2 and SnO2 oxides were formed after oxygen treatment at 520 K. The study proved the existence of strong Ce–Sn interaction and charge transfer from Sn to the Ce–O complex that lead to a weakening of the cerium–oxygen bond, and consequently, to the formation of oxygen deficient active sites on the ceria surface. This behavior can be a key for understanding the higher catalytic activity of the SnOx/CeOx mixed oxide catalysts as compared with the individual pure oxides.