Study on the surface properties of TiO₂-SnO₂ supported catalysts for low temperature selective catalytic reduction of NO_x

TiO₂-SnO₂ mixed oxide was prepared by a co-precipitation method and xCeO₂/TiO₂-SnO₂ catalysts were prepared using the impregnation method. The physicochemical properties were investigated by X-ray diffraction (XRD), BET specific surface area measurement, H₂ temperature-programmed reduction (H₂-TPR), NH₃ temperature-programmed desorption (NH₃-TPD), high-resolution transmission electron microscopy (HRTEM), and in situ diffuse reflectance infrared spectroscopy (DRIFTS). Meanwhile, their catalytic performance for the selective catalytic reduction of NO_x with NH₃(NH₃-SCR)was tested. It was found that 0.1Ce/TiO₂-SnO₂ had higher NO_x conversion and wider temperature range of 250~350℃. Excess loading of CeO₂ could lead to the decrease of specific surface area, redox ability and adsorption capacity of ammonia as well as the shrink of effective catalytic temperature range. NH₃-TPD result showed that the adsorption of NH₃ in weak acid and medium acid sites were significantly enhanced by CeO₂, which was related to the decrease of NH₃-SCR reaction temperature. In situ DRIFTS indicated that the strength of Lewis acid sites and Brønsted acid Sites were markedly enhanced for xCeO₂/TiO₂-SnO₂ catalyst. Besides, new Brønsted acid Sites appeared at 1657~1666cm^-1 and NH₄⁺ played the dominant role in the SCR reaction.