Promoted V2O5/TiO2 catalysts for selective catalytic reduction of NO with NH3 at low temperatures

Abstract The influence of varying the V 2 O 5 content (3–6 wt.%) was studied for the selective catalytic reduction (SCR) of nitrogen oxides by ammonia on heteropoly acid (HPA)- and tungsten oxide (WO 3 )-promoted V 2 O 5 /TiO 2 catalysts. The SCR activity and alkali deactivation resistance of HPA-promoted V 2 O 5 /TiO 2 catalysts was found to be much higher than for WO 3 - promoted catalysts. By increasing the vanadium content from 3 to 5 wt.% the catalysts displayed a two fold increase in activity at 225 °C and retained their initial activity after alkali doping at a molar K/V ratio of 0.181. Furthermore, the catalysts were characterized by N 2 physisorption, XRPD, NH 3 -TPD, H 2 -TPR, Raman, FTIR and EPR spectroscopy to investigate the properties of the catalysts. XRPD, Raman and FTIR showed that promotion with 15 wt.% HPA does not cause V 2 O 5 to be present in crystalline form, also at a loading of 5 wt.% V 2 O 5 . Hence, use of HPAs does not cause increased N 2 O formation or unselective oxidation of NH 3. NH 3 -TPD showed that promotion by HPA instead of WO 3 causes the catalysts to possess a higher number of acid sites, both in fresh and alkali poisoned form, which might explain their higher potassium tolerance. Ex-situ EPR spectroscopy revealed that HPA-promoted catalysts have higher V 4+ /V total ratios than their WO 3 -promoted counterparts. H 2 -TPR suggests that HPAs do not have a beneficial effect on the V 5+ -V 3+ redox system, relative to WO 3 .