The Poisoning and Desulfation Characteristics of Iron and Copper SCR Catalysts

A laboratory study was performed to assess the effects of SO 2 poisoning on the NO x conversion of iron (Fe) and copper (Cu) SCR catalysts. Thermally aged samples of the catalysts were poisoned with SO2 under lean conditions. At various times during the poisonings, the samples were evaluated for NOx conversion with NO and NH 3 using lean temperature ramps. The low temperature NO x conversions of both catalysts decreased by 10 to 20% after 1 to 4 hours of poisoning but were stable with continued exposure to the SO2. The poisoned Cu SCR catalyst could be desulfated repeatedly with 5 minutes of lean operation at 600°C. Initially, the poisoned Fe SCR catalyst required 5 minutes of lean operation at 750°C to recover its maximum NOx conversion. However, after multiple poisonings and desulfations, the low temperature NOx conversion of the catalyst exhibited significantly less sensitivity to the SO2, although the final NO x conversion following the 750°C desulfation also decreased slightly with the repeated poisonings and desulfations. This decrease in SO 2 sensitivity for the Fe SCR catalyst could potentially eliminate the need to desulfate this catalyst.