Copper-cerium oxide catalysts supported on monoclinic zirconia CuO/CeO2/ZrO2 were tested in the preferential oxidation of CO in hydrogen-rich gases and the optimal catalyst composition was determined. The state and the structure of copper species in the catalysts were investigated by X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) analysis. While a small amount of copper incorporated into the surface layers of the CeO2 lattice, the disordered oxide clusters were the main copper species in the catalysts with copper content <= 5 wt.%. The increase in the copper loading (> 10 wt.%) led to predominant formation of bulk CuO phase coupled with catalyst deactivation. (C) 2009 Elsevier B.V. All rights reserved.