Photocatalytic oxidation of gaseous toluene on titania/mesoporous silica powders in a fluidized-bed reactor

Abstract

The photocatalytic degradation of toluene was carried out on titania/mesoporous silica photocatalysts in a self-constructed gaseous fluidized-bed photoreactor equipped with UVA light source. The powder photocatalysts were synthesized by incorporation of aqueous titania sol (as a photoactive component), into silica mesoporous materials (as a high-surface-area support), via the sol–gel impregnation method. SBA-15 was used as an ordered and KIL-2 as a disordered mesoporous silica support. The Ti/Si nominal molar ratio was adjusted to 1/2, 1/1 and 2/1. The photocatalysts were characterized by X-ray diffraction (XRD), nitrogen sorption (BET), UV–vis–NIR diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FT-IR) and high-resolution transmission electron microscopy (HR-TEM). The effects of Ti/Si molar ratio and of the mesoporous silica structure were investigated measuring adsorption capacity and photocatalytic degradation of toluene. The rates of photocatalytic degradation reactions were found to be similar for photocatalysts with the same Ti/Si molar ratio independently of the mesoporous structure of silica. The adsorption capacity was decreasing as a function of the increasing Ti/Si molar ratio in the case of both types of mesoporous silica support. However, the photocatalytic degradation proceeded faster for the Ti/Si molar ratio 1/1 while, in the case of the other investigated Ti/Si molar ratios 1/2 and 2/1, the degradation rates were lower. In general, the photocatalytic activity was considerably improved by using supported titania–silica catalyst compared to an unsupported titania powder prepared from the same nanocrystalline titania sol.