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

摘要

The influence of varying the VO 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)-promoted VO/TiO catalysts. The SCR activity and alkali deactivation resistance of HPA-promoted V2O5/TiO2 catalysts was found to be much higher than for WO-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 physisorption, XRPD, NH-TPD, H-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 VO to be present in crystalline form, also at a loading of 5 wt.% VO. Hence, use of HPAs does not cause increased NO formation or unselective oxidation of NH. NH-TPD showed that promotion by HPA instead of WOcauses the catalysts to possess a higher number of acid sites, both in fresh and alkali poisoned form, which might explain their higher potassium tolerance. EPR spectroscopy revealed that HPA-promoted catalysts have higher V/V ratios than their WO-promoted counterparts. H-TPR suggests that HPAs do not have a beneficial effect on the V-V redox system, relative to WO.