Oxygen Mobility in CeO₂and Ce<i>_x</i>Zr₍₁_-<i>_x</i>₎O₂Compounds:  Study by CO Transient Oxidation and¹⁸O/¹⁶O Isotopic Exchange

Abstract

Cerium−zirconium mixed oxides (Ce x Zr (1 - x ) O 2 ), precalcined at 900 °C in dry air, were supplied by Rhodia Terres Rares as monophasic solid solutions. Introduction of some zirconium atoms in the ceria lattice by isomorphous substitution clearly influences the final properties of these materials as long as the cubic structure of ceria is maintained. Modifications in oxygen storage capacity (OSC measurements), redox properties (CO TPR), and oxygen exchange processes (TPIE) were studied. Ce 0.63 Zr 0.37 O 2 was shown to have the most promising properties with the largest OSC at 400 °C and the highest reactivity in O 2 exchange. All mixed oxides are able to exchange very large amounts of oxygen compared to ceria, implying the participation of bulk oxygen. Furthermore, on Ce x Zr (1 - x ) O 2 samples, oxygen is predominantly exchanged via a multiple heteroexchange mechanism involving surface dioxygen species as superoxides or peroxides.