CuO-CeO2 series catalysts are the effective catalysts for the selectiveCO oxidation in hydrogen-rich gas. The adsorption species on the CuO-CeO2catalysts doped with alkali and alkaline earth metal oxides were investigatedwith in situ diffuse reflectance FTIR spectroscopy (in-situ DRIFTS) technique.The results showed that a bane at 2 106 cm-1, due to the carbonyl species,appeared on the CuO-CeO2 catalysts. In the reaction atmosphere, the intensity ofthis band increased first and then decreased with increasing the temperatures. Itwas noted that the main active adsorption sites of the CuO-CeO2 catalysts wereCu+ species. At lower temperatures, the carbonyl species were desorbed from thesurface of CuO-CeO2 catalysts in the reversible form, while they were desorbedmainly in the irreversible form at the higher temperatures. A sharp peak at 3 660cm-1, attributed to the geminal Ce(OH)2 group, was also apparent on the surfaceof reduced CuO-CeO2 catalyst. The peaks at 1 568, 2 838 and 2 948 cm-1 wereattributed to formate species and the peaks centered at 1 257 and 1 633 cm-1 wereassigned to carbonate species. CO could react with the active hydroxyl speciesand generate formate species. At higher temperatures, the C—H bond of formatespecies could break and form carbonate species. These two species would decreasethe performance of CuO-CeO2 catalysts at higher temperatures. The stronger IRpeaks attributed to CO2 and formate species were observed, moreover there wasstill a weak IR peak assigned to carbonyl species for Cu1Li1Ce9Oδ catalyst whenthe temperature was above 180 ℃. It was shown that as the electron donor, thedoping of Li2O on CuO-CeO2 catalyst could contribute to the irreversibledesorption of CO at lower temperatures and inhibit the adsorption of H2 on thecatalytic surface, and benefit the formation of formate species as well. Althoughthe amounts of CO adsorption on Cu1Mg1Ce9Oδ and Cu1Ba1Ce9Oδ catalysts were muchmore than other catalysts at lower temperatures, they were mainly desorbed in thereversible form, which had no contribution to the selective CO oxidation.situ DRIFTS; Gas adsorption