Photocatalytic decomposition of benzene over TiO2 in a humidified airstream

Abstract

Photocatalytic decomposition of benzene over TiO₂ in the gas phase at room temperature was studied with a fixed-bed flow reactor. In a humidified airstream ([H₂O]=2.2%), benzene was efficiently decomposed to CO₂ and CO with the selectivities of 93 and 7%, respectively. The selectivities were almost independent of the benzene conversion, indicating that CO is not the intermediate of CO₂ in the reaction. The selectivity of CO was in the range of 7–10% with varying concentration of O₂, H₂O, and benzene. The formation of phenol and brownish carbonaceous matter attributable to polymeric products was observed on the catalyst surface. In the absence of O₂, benzene oxidation did not proceed at all, showing that O₂ is essential for the reaction. The presence of H₂O not only suppressed the formation of the carbon deposits on the catalyst surface, but also accelerated the decomposition of them to CO₂ and CO. Diffuse reflectance IR study showed that the presence of H₂O regenerated the surface hydroxyl groups of TiO₂ which were consumed in the photoreaction. With increase in the benzene concentration, the benzene conversion was decreased and the amount of carbon deposits on the catalyst surface was increased.