(143g) The Effect of Promoters on Catalytic Activity of Supported V2O5-WO3/TiO2 Catalysts for Selective Catalytic Reduction (SCR) of NO with NH3

The selective catalytic reduction (SCR) of environmentally undesirable NO_x with NH₃ to harmless N₂ and H₂O plays a crucial role in reducing NO_x acid gas emissions from large utility boilers, industrial boilers, municipal waste plants and incinerators. The supported V₂O₅−WO₃/TiO₂ catalysts have become the most widely used industrial catalysts for such SCR applications. The vanadium oxide-based catalysts exhibit reduction of NO_x in the operating temperature window of 300-500 °C. The goal of the recent research is to develop low temperature SCR catalyst systems that enhance the SCR activity of supported V₂O₅−WO₃/TiO₂ catalysts in the low temperature range (<300°C) and low vanadium oxide loading.

A series of promoted catalysts MO_x-V₂O₅-WO₃/TiO₂ catalysts (M=Si, Al, Cu, Ce, P, Zr etc.) were synthesized by aqueous incipient-wetness impregnation, drying at ~110°C and calcination in O₂ at 450°C. The promoters with ~20% or ~80% monolayer surface coverage were initially introduced onto TiO₂ support (P25). Subsequently, 1% V₂O₅ was impregnated onto the surface modified TiO₂ supports following by drying and calcining. A parallel series of promoted 1% V₂O₅ and 5% WO₃ catalysts were also prepared to examine the influence of the tungsten oxide promoter.

The promoted TiO₂-supported catalysts were characterized to better understand the influence of the promoters on the (1) surface VO_x structures, (2) surface acidity and (3) SCR catalytic activity in the low temperature range. The in situ Raman spectra reveal that the WO_x, SiO_x and AlO_x promoters oligomerize the surface VO_x sites (V=O vibration shifts from 1030 to 1034 cm^-1). The corresponding in situ IR spectra of adsorbed ammonia indicate that the ratio of surface Bronsted (NH₄⁺) and Lewis (NH₃) acid sites can be fine-tuned by adjusting the surface coverage of the promoters. Although these promoters enhanced the SCR activity, only the AlO_x promoter significantly enhanced the SCR activity at low temperatures (Al >> W ~ Si > no promoter). The results for the other promoters and the catalyst structure-SCR activity relationships will also be presented.

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