Copper-ceria catalysts with three different Cu loadings (1, 7 and 15 wt%) were prepared by incipient wet impregnation, dried at 120 degrees C and calcined in air at 500 degrees C. The as-prepared catalysts were characterized by XRD, BET, Diffuse Reflectance Spectroscopy (DRS-UV-visible), Raman spectroscopy, CO and H-2-TPR, CO-TPR, CO-TPD and Oxygen Storage Capacity (OSC) measurements (with CO and O-2 concentration step-changes). The results indicated a good dispersion of copper for catalysts with 1 and 7 wt% Cu; however, bulk CuO was present for catalyst with 15 wt% Cu loading. Catalyst with 7 wt% Cu was observed to have very high capacity to release lattice oxygen to oxidize CO at low temperature. Activity results for CO oxidation in the absence and in the presence of 60% H-2, demonstrated a very similar performance for catalysts with 7 and 15 wt% Cu (both with T-100 = 112 degrees C), and much better than that of catalyst loaded with 1 wt% Cu. Catalyst with 7 wt% of copper shows very high activity (100% in a wide temperature window) and selectivity (higher than 85%), which makes an attractive for its use in purification of hydrogen for fuel cell applications. The presence of a mixture of CO2 and H2O inhibited catalyst activity, with CuO/CeO2 catalyst with 7 wt% Cu exhibiting the best performance in the overall reaction temperature range. This could be attributed to the presence of highly disperse copper, only part of it in deep interaction with ceria. The effect Of O-2/CO ratio (lambda) and the potential reversibility of the inhibitory effect of CO2 and H2O were also investigated. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.