Improving the tolerance to alkali and alkaline earth metal chlorides of WO3 and Nb2O5 promoted V2O5/TiO2 catalysts for the NH3-SCR reaction

Abstract

V2O5-WO3/TiO2 catalysts are widely used to reduce NOx emissions from municipal solid waste incineration. However, the flue gas always contains different alkali and alkaline earth metal chlorides. In this work, we compared the effect of KCl, NaCl and CaCl2 on V2O5-WO3/TiO2 catalyst for the NH3 Selective Catalytic Reduction of NOx, and we aim to improve the tolerance of the catalyst by replacing WO3 with Nb2O5. It was found that KCl has the greatest poisoning effect, resulting in a severe decrease in the surface acidity, redox performance, V5+/V4+ ratio and surface adsorbed oxygen. The replacement of WO3 with Nb2O5 improved the activity and KCl tolerance of the catalyst owing to the improvement of surface acidity, redox performance, V5+ ratio and surface adsorbed oxygen. This may be due a more favorable interaction of K+ with Nb2O5 than with V2O5. In-situ DRITFS experiments showed that alkali (and alkaline earth) metal ions favor the transformation of adsorbed NO2 species into stable nitrates and nitrites. However, the replacement of WO3 with Nb2O5 would inhibit the formation of these stable species owing to an electronic effect of the promoter.