The role of H2O in the photocatalytic oxidation of toluene in vapour phaseon anatase TiO2 catalyst - A FTIR study

Photocatalytic oxidation of toluene has been carried out in a gas-solid reg ime by using polycrystalline anatase TiO2 in a fixed-bed continuous reactor . Air containing toluene and water vapours in various molar ratios was fed to the photoreactor irradiated by a medium pressure Hg lamp. Toluene was ma inly photo-oxidised to benzaldehyde, and small amount of benzene, benzyl al cohol and traces of benzoic acid and phenol were also detected. In the pres ence of water, no decrease of photoreactivity was observed at steady-state conditions. By removing water vapour from the feed, the conversion of tolue ne to benzaldehyde was almost completely inhibited, and an irreversible dea ctivation of the catalyst occurred. FTIR investigations indicated that benz aldehyde is photoproduced on the TiO2 surface even in the absence of water vapour, but exposure of the catalyst to the UV light in a dry atmosphere re sults in an irreversible consumption of surface hydroxyl groups. As these s pecies play a key role in the photoreactive process, this dehydroxylation s hould be the reason of the catalyst deactivation observed in the catalytic runs carried out in the absence of water vapour. (C) 1999 Elsevier Science B.V. All rights reserved.