Catalytic performance and hydrothermal durability of CeO2-V2O5-ZrO2/WO3-TiO2 based NH3-SCR catalysts

Ceria modified V2O5-ZrO2/WO3-TiO2 catalysts with different Ce loading (0, 5, 10 wt%) have been evaluated in the NH3-SCR process before and after hydrothermal aging (750 degrees C, 10 wt% H2O/air for 12 h). Compared with only Zr containing catalysts, addition of Ce greatly enhances the low temperature activity of the fresh catalyst, but it deactivates obviously after aging. The catalysts were characterized by XRD, XPS, H-2-TPR and DRIFTS. The results suggest that not only the enrichment of Ce3+ and the increased redox properties, but also the more active adsorbed nitrates on CeO2 modified catalysts benefit the SCR reaction. The catalyst deactivation after aging is mainly due to the sintering and segregation of CeO2 on the catalysts surface, suggesting the poor hydrothermal stability of the Ce component. However, additional provided NO2 will compensate for the activity loss due to hydrothermal aging and significantly improve the low temperature SCR activity, suggesting a high NO2 sensitivity of the Ce component. Moreover, it was found that a ceria, zirconia containing catalyst exhibits superior SCR activities, with both the fresh and aged 1%V2O5-10%CeO2-10%ZrO2/WO3-TiO2 catalysts showing high NOx conversions (>95%) and selectivity to N-2 (>98%) in a wide temperature range of 200-500 degrees C, at a space velocity of 120 000 h(-1) in a simulated exhaust containing 500 ppm NOx (NO2/NO = 1) and 5% H2O.