The adsorption of CO (10% CO/He) on pure ZrO2 aerogel and on a 0.5% Pt/ZrO2 solid is studied at 638 K using in situ FTIR. It is shown that the two solids lead to the formation of the same adsorbed species: formate and carbonate species, in comparable superficial concentration. On ZrO2, the formate species are not hydrogenated in presence of pure hydrogen at 544 K. On Pt/ZrO2, they are hydrogenated at 544 K into adsorbed methoxy groups by hydrogen spilled over species. The methoxy groups are hydrogenated into methane by a process which probably involves a reverse spillover.