A modified citrate method incorporating hydrothermal treatment of the precursors has been employed for the synthesis of CuO-CeO2 catalysts with varying CuO content. Catalyst characterization was done by N-2 physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and H-2-TPR. The activity and selectivity of the catalysts for the selective oxidation of CO in excess H-2 was examined employing a simulated reformate gas mixture. Hydrothermal treatment of the citrate precursors was found to induce more efficient mixing of Cu2+ and Ce4+ ions in the precursor compound. CuO-CeO2 catalysts containing highly dispersed, XRD-invisible CuO species were synthesized with this method at even higher CuO contents than those reported previously. Interaction between CuO and CeO2 leads to structural and thermal stabilization of the catalysts, while surface segregation of Cu2+ ions takes place in all cases. CUO-CeO2 catalysts are significantly more active, more selective and less inhibited by CO2 than pure CuO. The activation temperature and the CuO content of the catalysts seem to play an important role by influencing, on one hand, the degree of interaction between CuO and CeO2 and, on the other hand, the phenomena of sintering and surface area loss. (c) 2006 Elsevier B.V. All rights reserved.