Selective catalytic reduction (SCR) is widely used to control NOx emissions from power plants and industrial boilers. Supported V2O5−WO3/TiO2 catalysts have become the most widely used industrial catalysts for such stationary SCR applications. Sulfur dioxide (SO2) is initially formed by the oxidation of sulfur contained in fuels, such as coal and heavy fuel oil, and is easily oxidized to sulfur trioxide (SO3). The oxidation of SO2 to SO3 during SCR, however, is undesirable owing to the formation of acidic vapor phase SO3/H2SO4 and surface sulfates that poison the catalysts. The objective of this research is to study the effect of surface metal oxide promoters on the sulfur oxide resistance of supported V2O5-WO3/TiO2 catalysts for the SCR reaction. A series of promoted catalysts MOx-WO3-V2O5/TiO2 catalysts (M= Ce, Cu, Si, Al, P, Zr etc.) were synthesized by aqueous incipient-wetness impregnation. Initially, the TiO2 support (Evonik P-25; ~55 m2/g; ~80% anatase and ~20% rutile) was impregnated either 20% or 80% monolayer surface coverage of CeO2, CuO, SiO2, Al2O3, P2O5 or ZrO2 and calcined at 450oC. Subsequently, 1% V2O5 and 5% WO3 were impregnated onto the surface modified TiO2 supports and calcined at 450oC. Lastly, 1.5% SOx (ammonium sulfate) was impregnated onto WO3-V2O5/TiO2 and calcined at 450oC. The promoted TiO2-supported catalysts were characterized to understand the influence of the promoters on the (1) surface VOx structures, (2) surface acidity and (3) SCR catalytic activity. In situ Raman spectra reveal that all the active components were well dispersed on the catalyst surface since crystalline nanoparticles were not present. The slight blue shift of the terminal V=O band (from 1028 to 1035 cm-1) after the impregnation of WO3 reflects the oligomerization of surface VO4 sites in the presence of the surface WOx sites. The corresponding in situ IR spectra of adsorbed ammonia chemical probe molecule indicate that the ratio of surface Bronsted (NH4+) to Lewis (NH3) acid sites can be fine-tuned by adjusting the surface coverage of the promoters. The Ce, Cu and Si-promoted catalysts significantly enhanced the SCR activity at low temperatures. In the presence of surface sulfate, the Ce, Cu, Si, Zr-promoted catalysts were more active than SOx-free catalysts at lower temperatures. The effect of surface sulfates upon the SCR reaction and the catalyst structure-SCR activity relationships will also be presented.

Effect of promoters on the sulfur resistance of supported V2O5-WO3/TiO2 catalysts for selective catalytic reduction (SCR) of NO with NH3

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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