Kinetic modeling of benzyl alcohol and/or benzaldehyde selective oxidation in water by means of TiO2/CuII/hn process

The mechanism of photocatalytic selective oxidation of benzyl alcohol to benzaldehyde and benzaldehyde to benzoic acid by means of cupric ions is investigated in the presence of TiO2 catalyst in water at pH = 2.0 and under deareated conditions. A competitive adsorption is proposed in which the aromatic substrates adsorb on TiO2 surface and react with the positive holes whereas CuII ions are reduced to Cu0 by the photogenerated electrons. A new kinetic model is developed by writing a set of mass balance equations for the main species involved in the photocatalytic oxidation process. The resulting mathematical model is used for the analysis of the data collected at different starting substrates' concentrations and predicts satisfactorily the concentrations of CuII species, organic substrates and intermediates during each of the selective photo-oxidation runs. The effect of SO 4 2 - and H 2 PO 4 - species, which compete with benzyl alcohol and benzaldehyde for the reaction with positive holes on the catalyst surface and behave as scavengers towards HO radicals, is taken into account in the model. The values of some rate constants of the reactions of the holes with benzyl alcohol, benzaldehyde, CuI species and inorganic anions (SO 4 2 - and H 2 PO 4 -), not available in the literature, are estimated by a proper optimizing procedure.