Photochemical oxidation of styrene in acetonitrile solution in presence of H2O2, TiO2/H2O2 and ZnO/H2O2

The photochemical oxidation of styrene under UV-A irradiation in acetonitrile solution containing H2O2 was investigated in absence or in presence of TiO2 or ZnO. The effects of the molar ratio H2O2/styrene and of the pH on the disappearance rate and on the selectivity into benzaldehyde and benzene oxide were investigated. Under H202/UV, a conversion of about 6% and a total selectivity into benzaldehyde was observed. In presence of TiO2 the conversion is multiply by 2 and styrene oxide was detected. However, its selectivity is only 10%. At basic pH, in presence of TiO2 or ZnO, the conversion of styrene are 47% and 60% respectively. A similar selectivity of styrene oxide (50%) was found for the both catalysts. However, in presence of TiO2 benzoic acid is formed with a selectivity of 20% whereas only benzaldehyde was found on ZnO. The impact of the nature of the catalyst and of the active species generated under irradiation were suggested for explaining the difference of reactivity observed. A mechanism of the formation of benzaldehyde and styrene oxide in absence or presence of photocatalyst and of NaOH was proposed. (C) 2017 Elsevier B.V. All rights reserved.