Modification of the V2O5-WO3/TiO2 catalyst with Nb to reduce its activity for SO2 oxidation during the selective catalytic reduction of NOx

Abstract

A series of Nb-modified V2O5-WO3/TiO2 catalysts were prepared by the impregnation method and the effect of Nb loading on their SO2 oxidation activity during the selective catalytic reduction of NOx was investigated. The results indicate that the Nb2O5-V2O5-WO3/TiO2 catalyst with a Nb2O5 loading of 2% exhibits the lowest SO2 conversion of 0.6% for oxidation at 350 °C, whereas the conversion of NOx is still above 95%. The catalysts were characterized by TGA, BET, XRD, H2-TPR, CO2-TPD, XPS and in-situ DRIFTS. The results illustrate that the influence of Nb modification on the crystal structure of V2O5-WO3/TiO2 catalyst is rather insignificant; however, the surface area of the Nb2O5-V2O5-WO3/TiO2 catalyst decreases slightly after the modification with Nb, conducing to a decrease of SO2 adsorption on the catalyst. Meanwhile, the content of oxygen adsorbed on the catalyst surface decreases considerably upon the Nb modification, suggesting a weakened redox performance, which is beneficial to reducing the oxidation of SO2. The in-situ DRIFTS results illustrate that the content of the intermediate VOSO4 product on the catalyst surface decreases over the Nb-modified Nb2O5-V2O5-WO3/TiO2 catalyst, leading to a decrease of SO3 production.