The photocatalytic activity of TiO2 (Degussa P-25) in the mineralization of maleic acid in aqueous solution at pH = 3 is greatly enhanced by the previous adsorption of alummium(III) on the catalyst surface. The nature of the intermediates detected during maleic acid degradation is also affected by the presence of Al(III). The observed differences can be related to an oxygen reactivity enhancement. The effect of aluminium(III) in the maleic acid adsorption over the TiO2 surface has also been investigated by using the ATR-FT-IR technique. The UV-vis diffuse reflectance spectra of the catalyst shows a red shift due to aluminium adsorption. At neutral pH, the positive effect of adsorbed Al(III) is not observed. (C) 2004 Elsevier B.V. All rights reserved.