Surface characterization of alumina-supported ceria

Abstract

CeO2/Al2O3 samples were characterized by XPS, Raman spectroscopy, and TPR. Three cerium species were detected, namely, a CeAlO3 precursor in the dispersed phase, small CeO2 crystallites, and large CeO2 particles. The CeAlO3 precursor is so named because it gives a Ce(III)-like XPS spectrum and a completely different Raman spectrum from that of CeO2, while TPR reveals that this species is more easily reduced to CeAlO3 than the CeO2 particles on alumina. It was also found that ceria in the CeAlO3 precursor and in a small crystallite form can be transformed to surface CeAlO3 upon H2 reduction at temperatures higher than 600°C, while even a partial conversion to CeAlO3 for bulk CeO2 requires a temperature above 800°C. CeAlO3 thus formed shows good thermal stability in air in the temperature range up to 600°C. © 1988 American Chemical Society.