Mixed copper aluminium oxide has been studied by XPS. It was shown that the reduction under hydrogen of the precursor oxide leads to the formation of cuprous ions located in the octahedral sites of the spinel matrix γ-A1203and hydridic species stored in the solid. The use of the pre-reduced compound at 300°C before catalysis with H2/CO is necessary to maintain almost intact the spinel phase despite the formation of metallic copper, whereas a strong modification of a surface composition was obseved when the solid is directly treated by H2/CO mixture.