Redox and Catalytic Properties of RhxCe1–xO2−δ Solid Solution

In this work, a detailed study of the redox properties of solid solution RhxCe1–xO2−δ in correlation with its catalytic activity in CO oxidation reaction was carried out. The ex situ X-ray photoelectron spectroscopy technique was applied to follow the charging states of the elements on the surface during the redox treatments at a temperature range of 25–450 °C. The results were compared with the data of temperature-programmed reduction by CO. The dissolution of rhodium in the ceria bulk considerably increased the mobility of CeO2 lattice oxygen, with redox transitions Ce4+ ↔ Ce3+ and Rh3+ ↔ Rhnδ+ observed already at low temperatures (below 150 °C). The reduced rhodium clusters (Rhnδ+) formed during the reduction treatment significantly improved the catalytic activity of the RhxCe1–xO2−δ solid solution. The small size of the rhodium clusters (Rhnδ+) and high defectiveness of the fluorite phase provided the reversibility of Rhnδ+/CeO2 ↔ RhxCe1–xO2−δ transitions upon redox treatment, resulting in the high re...