PROX reaction over Co catalysts supported on ceria nano-particles was investigated with a special focus on the effect of Co loading. High surface area ceria nano-particles were prepared through a precipitation technique using cerium (Ill) nitrate hexahydrate and sodium hydroxide. Co incorporation was achieved using a wet impregnation method in aqueous media. Catalysts were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction, dispersion measurements, and in situ diffuse reflectance Fourier transform infrared spectroscopy and X-ray absorption spectroscopy. Activity and selectivity of CoOx/CeO2 catalysts with different Co loadings showed higher Co loadings to favor higher CO oxidation at the expense of oxygen selectivity. Higher activation energies for H-2 oxidation compared to CO oxidation were observed, regardless of the Co loading, implying a higher temperature sensitivity for the H-2 oxidation reaction. The Co phase was identified as Co3O4 and was stable in the reducing environments present in PROX reactions. (C) 2012 Elsevier B.V. All rights reserved.