The redox properties of ceria-zirconia solid solutions have been often investigated [1] because of their peculiar behaviour: a promotion of the reduction at lower temperature is observed after a reduction at high temperature (>900K) and a reoxidation under relatively mild conditions (400K-900K). These properties are related with structural bulk modifications, i.e. the formation of more reducible pyrochlore phases [2]; however, the redox promotion is observed also in the presence of very slight structural rearrangements [3], the influence of which on the redox and transport properties is still unclear. The recent observation of formation of pyrochlore nuclei at low temperature indicated that the promotion is likely correlated to the surface activation [3, 4, 5]. In order to elucidate the mechanism of this promotion, we adopted a different approach, by carrying out TPR measurement on dense pellets rather than on powder samples, in order to normalize and amplify both the influence of the surface properties on the reaction and the ion migration path.
