The reactivity towards O₃ of the different species formed from phenol adsorption on silica and ceria has been studied using IR spectroscopy by increasing the temperature from 77 K. It clearly appeared that on silica H-bonded phenol species were more reactive than phenoxy species, whereas on ceria monodentate phenoxy species were more active than bidentate species. Intermediate products of phenol oxidation were characterized by bands between 1800 and 1600cm^-1, that at 1750cm^-1 being probably due to the formation of acarboxylic acid.