Photocatalytic degradation of gaseous benzene over TiO 2/Sr 2CeO 4: Kinetic model and degradation mechanisms

Abstract

Photocatalytic oxidation of benzene in air was carried out over TiO 2/Sr 2CeO 4 catalysts. The prepared photocatalyst was characterized by S BET, UV–vis diffuse reflectance and XPS. TiO 2/Sr 2CeO 4 absorbs much more visible light than TiO 2 in the visible light region. The XPS spectrum shows that the binding energy value of Ti 2p 3/2 transfers to a lower value. The main purpose was to investigate the kinetic model and degradation mechanisms. The kinetic data matched well with the Langmuir–Hinshelwood (L–H) kinetic model with the limiting rate constant and the adsorption constant in this case were 0.0064 mg l −1 min −1 and 9.2078 l mg −1, respectively. No gas-phase intermediates were detected by direct GC/FID analysis under the conditions despite the high benzene concentration. Ethyl acetate and (3-methyl-oxiran-2-yl)-methanol were two major identified intermediates which were accompanied by butylated hydroxytoluene, 2,6-bis(1,1-dimethylethyl)-4,4-dimethylycyclohe, 2,5-cyclohexadiene-1,4,dione,2,6-bis(1,1-dim). It is plausible that at least one of these less-reactive intermediates caused the deactivation of the photocatalyst. Finally, the photocatalytic oxidation mechanisms were speculated.