The interaction between carbon monoxide and oxygen at room temperature on a chromia-silica catalyst has been studied by infrared spectroscopy. Only the adsorbed CO which causes the band at 2187 cm-1 actively participates in the oxidation reaction, thus acting as an intermediate of great activity. Oxygenated species, mainly of the carboxylate type, have also been detected in the 1800-1300-cm-1 frequency range.