The species formed by interaction of carbon monoxide with CuO/ZrO2 and CuO/ZnO/ZrO2 aerogel catalysts are mainly of the carbonate type and not of the formate type, in contrast to the behaviour of ZrO2 and ZnO/ZrO2 aerogels (D. Bianchi, T. Chafik, M. Khalfallah and S.J. Teichner, Appl. Catal. A, 105 (1993) 223). The presence of copper oxide in the catalysts imposes an irreversible adsorption at 25-degrees-C of carbon monoxide on Cu2+ ions in the form of carbonyl type species which is transformed into carboxylate and, by oxidation, into carbonate type species. The spillover from copper to zirconium ions of the species derived from the solid and the carbon monoxide is envisaged.