The role of molybdenum on the enhanced performance and SO2 resistance of V/Mo-Ti catalysts for NH3-SCR

Abstract

The influence of molybdenum on the selective catalytic reduction (SCR) performance and SO2 durability of V/Mo-Ti catalysts was investigated. The characteristics of the catalysts were investigated by Brunauer-Emmett-Teller (BET) surface area analysis, field-emission transmission electron microscopy (FE-TEM), Raman spectroscopy, NH3-temperature programmed desorption (NH3-TPD), in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTs), SO2 temperature-programmed desorption (SO2-TPD), and X-ray photoelectron spectroscopy (XPS). The V/Mo-Ti catalysts exhibited improved SCR performances and SO2 resistances at 250 °C compared to those of V/W/Ti catalysts. The improved catalytic activity was shown to be imparted by amorphous MoOx. The formation of amorphous MoOx species with the addition of molybdenum to titanic acid was found to be more significant than that by the addition of molybdenum to crystalline TiO2. The increased density of NH3-adsorption and Brønsted-acid sites by addition of molybdenum was found to have a positive effect on catalyst performance. Since the reaction between SO2 and VOx was suppressed by the addition of molybdenum, the area of the SO2-TPD peak due to desorption of adsorbed SO2 from the catalyst surface was reduced. This decrease in the amount of adsorbed SO2 improved the SO2 resistances of the catalysts. The V/Mo-Ti catalysts exhibited increasing activities and SO2 resistances with increasing Mo6+ ratio (and Mo6+ atoms/cm3). Furthermore, they exhibited suppressed formation of ammonium sulfate salts due to decreased SO2 adsorption, as the reaction of terminal VO groups and adsorbed SO2 is inhibited by the addition of molybdenum. Thus, the V/Mo-Ti catalysts exhibited better catalytic activities and SO2 durability than those of V/W/Ti catalysts.