Nanosized CeO2 and CuO/CeO2 samples. active for CO-PROX or related processes were comparatively examined by O-2 probe electron paramagnetic resonance and in situ Raman and X-ray diffraction techniques. Their behavior toward CO reduction, as well as the oxygen-handling properties of the CO-reduced samples, was explored. An appreciable reduction Of the ceria bulk was detected on treatment under CO Lit 473 K. On the basis of the analysis of the evolution of different oxygen-derived species (superoxide, peroxide, O-) on low-temperature (77-300 K) oxygen chemisorption on the CO-reduced samples, a general picture of the redox properties of the samples is presented. Results demonstrate that the presence of copper promotes completion of the redox cycle under CO/O-2 by favoring both ceria reduction and oxidation. This can be relevant to explaining the remarkable oxidation activity and synergetic effects observed for catalysts combining CuO and CeO2. (c) 2006 Elsevier Inc. All rights reserved.