Photocatalytic oxidation in the presence of microwave irradiation: observations with ethylene and water

Microwave irradiation was employed in the heterogeneous photocatalytic oxidation (PCO) of a test compound, ethylene, in the gas phase on TiO2/ZrO2 mixed oxide thin films prepared via sol-gel processing. This approach was taken to study the rate of PCO of these compounds as a function of water concentration by perturbing the presence of water on the surface of the catalyst, PCO experiments were conducted with two types of reactor assemblies (Approaches I and 2), In Approach I when microwave plasma lighting was applied, microwave irradiation increased the rate constants by 15% (alpha = 1) and 26.9% (alpha = 0.5) corrected for light irradiance in studies conducted at 15% relative humidity RH), but had a negligible effect at 0 and 5% RH. In Approach 2, with (be light source external to the microwave chamber, the degradation of ethylene with 3 mul liquid water injection proceeded faster (83.9%) in the presence of the microwave irradiation than in the absence. Measurements of water adsorption indicated that microwave irradiation facilitated the removal of excess water from the catalyst surface treated with UV illumination in studies with the RH above 15%, but excess water removal was not observed in studies with the RH lower than 5%. Contact angle measurements helped to elucidate the effect of surface wettability of TiO2/ZrO2 catalyst films on the observed results. (C) 2002 Elsevier Science B.V. All rights reserved.