The reducibility of Ce-Al-O and Cu-Ce-Al-O solids is studied by H-2-TPR and EPR in order to identify the different ceria and copper oxide species. The study of Ce-Al-O oxides shows that dispersion of ceria on alumina improves reducibility of ceria bulk and stabilizes surface ceria. Concerning quantitative results, ceria reduction extent is more important for Ce-Al-O oxides than for pure ceria. This result can be related to the dispersion of ceria on alumina which decreases ceria crystallites size and enhances the ceria bulk reduction. For ternary oxides, copper oxide and ceria interact strongly. Introduction of copper facilitated ceria reduction, and quantitatively, the presence of copper favors the total reduction of ceria contrary to Ce-Al-O oxides. When ceria loading is low, two copper species are identified, and are attributed to small clusters and highly dispersed copper oxides. During the reduction of copper species, a partial reduction of ceria is observed. Increasing of copper loading leads to the formation of CuO aggregates. (C) 2004 Kluwer Academic Publishers.