A comparative study of Cu/Al2O3 (CuA) and Cu/CeO2/Al2O3 (CuCA) catalysts, examining the redox processes induced by thermal treatments in CO on preoxidized samples, has been performed by means of temperature-programmed techniques (TPR, TPO, and TPD) and FTIR and EPR spectroscopies. The results evidence different chemical behaviors of the copper entities as a function of their dispersion degree and interactions with the different components of the support. For CuA, three types of Cu2+ entities are evidenced, showing different dispersion degree and different reducibilities in CO. Clustered Cu2+ species are shown to be more easily reduced than isolated Cu2+ ions. For CuCA, part of the copper ions interact with the ceria component, as revealed in the initial calcined samples by the lower overall intensity of Cu2+ observed by EPR and by the formation of specific surface carbonyl complexes, upon CO adsorption, giving an FTIR band at 2105 cm(-1). These results are attributed to the presence of copper ions, interacting with large three-dimensional-like ceria particles (3D-Ce), which are reduced by CO at T-r less than or equal to 473 K, yielding metallic copper particles evidenced by specific carbonyl bands in the FTIR spectra. The results also indicate that the reduction of the copper species located in contact with more dispersed two-dimensional-like ceria entities (2D-Ce) can be favored by the effect of this contact. This easier reduction of copper interacting with ceria is presumed to favor the catalytic activity of CuCA for CO oxidation.