Photocatalytic oxidation of NOx over TiO2/HZSM-5 catalysts in the presence of water vapor: Effect of hydrophobicity of zeolites.

TiO(2) hybridized with HZSM-5 zeolites photocatalysts were prepared by a simple solid state dispersion method. The physicochemical properties of the catalysts were characterized by X-ray diffraction, UV-vis diffuse reflectance and FT-IR spectroscopy. The photocatalytic oxidation of NO(x) over TiO(2)/HZSM-5 having different Si/Al ratios was carried out under various levels of humidity and different pre-adsorption times in dark. The TiO(2)/HZSM-5 composite catalysts exhibited higher NO conversion and lower NO(2) formation than pure TiO(2). Pre-adsorption with water vapor and the high humidity during the photoreaction were harmful to the reactivity of TiO(2) hybridized with hydrophilic HZSM-5 zeolite. However, the photocatalytic reactivity of TiO(2) hybridized with hydrophobic zeolite varied little with increase in humidity. The results indicated that the high photocatalytic reactivity of TiO(2)/HZSM-5 catalysts is largely depended on the hydrophobicity of the zeolites.