Catalytic performance and hydrothermal durability of CeO sub(2)-V sub(2)O sub(5)-ZrO sub(2)/WO sub(3 )-TiO sub(2) based NH sub(3)-SCR catalysts

Ceria modified V sub(2)O sub(5)-ZrO sub(2)/WO sub(3)-TiO sub(2 ) catalysts with different Ce loading (0, 5, 10 wt%) have been evaluated in the NH sub(3)-SCR process before and after hydrothermal aging (750 degree C, 10 wt% H sub(2)O/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 sub(2)-TPR and DRIFTS. The results suggest that not only the enrichment of Ce super(3+) and the increased redox properties, but also the more active adsorbed nitrates on CeO sub(2) modified catalysts benefit the SCR reaction. The catalyst deactivation after aging is mainly due to the sintering and segregation of CeO sub(2) on the catalysts surface, suggesting the poor hydrothermal stability of the Ce component. However, additional provided NO sub(2) will compensate for the activity loss due to hydrothermal aging and significantly improve the low temperature SCR activity, suggesting a high NO sub(2) 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%V sub(2)O sub(5)-10%CeO sub(2)-10%ZrO sub(2)/WO sub(3)-TiO sub(2) catalysts showing high NO sub(x) conversions (>95%) and selectivity to N sub(2) (>98%) in a wide temperature range of 200-500 degree C, at a space velocity of 120 000 h super(-1) in a simulated exhaust containing 500 ppm NO sub(x) (NO sub(2)/NO = 1) and 5% H sub(2)O.