New Insight into SO_2 Poisoning and Regeneration of CeO_2-WO_3/TiO_2 and V_2O_5-WO_3/TiO_2 Catalysts for Low-Temperature NH_3-SCR

摘要

In this study, the poisoning effects of SO_(2) on the V_(2)O_(5)–WO_(3)/TiO_(2) (1%VWTi) and CeO_(2)–WO_(3)/TiO_(2) (5%CeWTi) selective catalytic reduction (SCR) catalysts were investigated in the presence of steam, and also the regeneration of deactivated catalysts was studied. After pretreating the catalysts in a flow of NH_(3) + SO_(2) + H_(2)O + O_(2) at 200 °C for 24 h, it was observed that the low-temperature SCR (LT-SCR) activity decreased significantly over the 1%VWTi and 5%CeWTi catalysts. For 1%VWTi, NH_(4)HSO_(4) (ABS) was the main product detected after the poisoning process. Both of NH_(4)HSO_(4) and cerium sulfate species were formed on the poisoned 5%CeWTi catalyst, indicating that SO_(2) reacted with Ce~(3+)/Ce~(4+), even in the presence of high concentration of NH_(3). The decrease of BET specific surface area, NO_(x ) adsorption capacity, the ratio of chemisorbed oxygen, and reducibility were responsible for the irreversible deactivation of the poisoned 5%CeWTi catalyst. Meanwhile, the LT-SCR activity could be recovered over the poisoned 1%VWTi after regeneration at 400 °C, but not for the 5%CeWTi catalyst. For industrial application, it is suggested that the regeneration process can be utilized for 1%VWTi catalysts after a period of time after NH_(4)HSO_(4) accumulated on the catalysts.