Modification of CeO2-ZrO2 mixed oxides by coprecipitated/impregnated Sr: Effect on the microstructure and oxygen storage capacity

Strontium was introduced to modify CeO₂-ZrO₂ mixed oxides (CZ) by two methods, coprecipitation (CZS) and impregnation (SCZ). Structural and textural characterizations revealed that Sr could retard the sintering of oxide particles and restrict the phase segregation during the hydrothermal ageing treatment. Specifically, the impregnation method brought about a more satisfying thermal stability of the modified CZ. This phenomenon was attributed to the enrichment of Sr on the particle surface and the formation of SrZrO₃ phase. The reducibility of the oxides was investigated by means of the oxygen storage capacity (OSC), and aged SCZ (SCZa) presented the best OSC performance. The reduction-ratio-dependent activation energy (E_a) was extremely low for the surface reduction of SCZa, suggesting the participation of highly active oxygen. The SrZrO₃/CeO₂-ZrO₂ interface was considered as the possible origin of this oxygen species. During bulk reduction, the effect of Sr on enhancing the reducibility was evident as well. © 2008 Elsevier Inc. All rights reserved.