Photocatalytic gas-phase detoxification of air streams contaminated with toluene: Kinetics studies

A thin-film coated catalyst reactor was used to investigate the gas-phase photocatalytic oxidation of toluene over two semiconductor catalysts, titanium dioxide and an 8% silica-titania binary oxide. When this reactor was used two reaction regimes were observed: the bulk transport regime and the surface controlled reaction regime. The surface reaction controlled regime was of most interest since mass transfer effects are eliminated.; Experiments performed using both catalysts under study showed that the SiO₂-TiO₂ binary oxide is more active and deactivates at a slower rate than the TiO₂ catalyst. Loss of activity for both catalysts was due to poisoning with a first order poisoning decay rate. Fitting the experimental data to this model enabled the prediction of the toluene initial conversion.; A suitable model that could predict the reaction kinetics adequately was not found. The dependence of the reaction rate on toluene initial concentration gave an order of 0.3 for SiO₂-TiO, with a rate of reaction constant (k) of 3.1 × 10–1 kmol 0.7-m/(kg-h), for a concentration range of 50 to 150 ppmv. This suggested that some toluene adsorption was taking place over the catalyst surface. The reaction rate for the TiO₂ catalyst was apparently zero order for the 50 to 100 ppm concentration range. The value of k obtained for this catalyst using this model was 4.5 × 10–4 kmol0.9-m0.3/kg-h.; Gaseous products encountered for this reaction with both catalysts benzaldehyde, carbon monoxide, carbon dioxide and water.