The activity of a Pd/Ce0.68Zr0.32O2 catalyst was studied under complex gas mixtures simulating those in automotive exhaust gases, analysing the evolution of CO, C3H6, O-2 and NO conversion and nitrogen compounds formed. The effects of pre-reduction and ageing treatments in cycled redox feedstreams at 1173 K, where the composition of oxidizing and reducing streams and cooling environment were changed, were investigated. The obtained results are compatible with the presence of two active palladium species on the catalyst surface whose predominance is temperature-dependent: Pd(I)-like species in the low-temperature range, and Pd(0) in the high temperature range. (C) 2011 Elsevier B. V. All rights reserved.