A highly active CoO/CeO2 nanoparticle catalyst with high surface area (78 m(2)/g) has been prepared and tested in the preferential oxidation of carbon monoxide (PROX) in the presence of hydrogen Three distinct temperature regions of catalyst activity are observed corresponding to CO oxidation, H-2 oxidation and methanation. The catalyst achieves near 100% CO conversion under a wide range of reaction conditions demonstrating peak activity near 175 degrees C The catalyst is stable with time-on-stream at the temperature of highest CO conversion The presence of H-2 decreases the CO oxidation rate, possibly clue to competitive adsorption between H-2 and CO CO oxidation and H-2 oxidation activation energies were 52 and 74 kj/mol, respectively Raman spectroscopy and X-ray diffraction experiments have demonstrated that the cobalt takes the form of Co3O4 and no CoO was detected under any experimental conditions (C) 2010 Elsevier B V All rights reserved