The reactivity towards O-3 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 II-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 1600 cm(-1), that at 1750 cm(-1) being probably due to the formation of a carboxylic acid.