The Poisoning and Desulfation Characteristics of Iron and Copper SCR Catalysts

A laboratory study was performed to assess the effects of SO₂ 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 NO_x conversion with NO and NH₃ 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 NO_x conversion. However, after multiple poisonings and desulfations, the low temperature NO_x 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 SO₂ sensitivity for the Fe SCR catalyst could potentially eliminate the need to desulfate this catalyst.