New Insight into SO 2 Poisoning and Regeneration of CeO 2 -WO 3 /TiO 2 and V 2 O 5 -WO 3 /TiO 2 Catalysts for Low-Temperature NH 3 -SCR.

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.