NH3-SCR performance and the resistance to SO2 for Nb doped vanadium based catalyst at low temperatures.

Niobium oxide as the promoter was doped in the V/WTi catalyst for the selective catalytic reduction (SCR) of NO. The results showed that the addition of Nb2O5 could improve the SCR activity at low temperatures and the 6wt.% additive was an appropriate dosage. The enhanced reaction activity of adsorbed ammonia species and the improved dispersion of vanadium oxide might be the reasons for the elevation of SCR activity at low temperatures. The resistances to SO2 of 3V6Nb/WTi catalyst at different temperatures were investigated. FTIR spectrum and TG-FTIR result indicated that the deposition of ammonium sulfate species was the main deactivation reason at low temperatures, which still exhibited the reactivity with NO above 200°C on the catalyst surface. There was a synergistic effect among NH3, H2O and SO2 that NH3 and H2O both accelerated the catalyst deactivation in the presence of SO2 at 175°C. The thermal treatment at 400°C could regenerate the deactivated catalyst and get SCR activity recovered. The particle and monolith catalysts both kept stable NOx conversion at 225°C with high concentration of H2O and SO2 during the long time tests.