Modification of the oxygen storage capacity of CeO2-ZrO2 mixed oxides after redox cycling aging

High surface area CcO(2)-ZrO2 mixed oxides were treated at 900-950 degrees C either under wet air or under successive reducing and oxidizing atmospheres in order to study the evolution of the oxygen storage capacity (OSC) of these solids after different aging treatments. Several complementary methods were used to characterize thr: redox behavior: temperature programmed reduction (TPR) by H-2, TPO, magnetic susceptibility measurements to obtain the Ce3+ content, FT-IR spectroscopy of adsorbed methanol and a method to compare the oxygen buffering capacity (OBC) of the oxides. All the results confirm that the mixed oxides exhibit better redox properties than pure ceria, particularly after aging. The enhancement in the OSC at moderate temperature has to be related to a deeper penetration of the reduction process from the surface into the under-layers. Redox cycling aging promotes the reduction at low temperature of all the mixed oxides, the improvement being much more important for low surface area aged samples. The magnitude of this effect does not depend on the BET surface areas which have similar values after cycling. This underlines the critical influence that the preparation and activation procedure have on the final OSC behaviors of the ceria-zirconia mixed oxides. (C) 2000 Elsevier Science B.V. All rights reserved.