New Insight into the Effects of NH3 on SO2 Poisoning for In Situ Removal of Metal Sulfates in Low-Temperature NH3-SCR over an Fe-V Catalyst

SO2 poisoning is a significant challenge for low-temperature selective catalytic reduction of NOx with NH3. Fundamental understanding of such sulfation effects on the catalyst is an essential step for finding strategies to overcome the issue. Here, the effect of NH3 on the temperature-driven sulfation process is systematically investigated over an Fe-V catalyst composed of alpha-Fe2O3 and FeVO4. When poisoning occurred by SO2 + O-2, the highly dispersed and thermally stable Fe-2(SO4)(3) species would be formed on the catalyst surface. Such poisoning was getting worse with the increase of sulfation temperature, inducing the continuous lowering of redox properties, NOx activation ability, and thereby the low-temperature catalytic performance. With introduction of NH3, additional ammonium sulfates species were simultaneously generated at lower temperatures (<250 degrees C), covering the surface reaction sites and thus aggravating the decline of low-temperature activities. Whereas the formation of Fe-2(SO4)(3) species would be dramatically suppressed at higher sulfation temperatures (>= 250 degrees C), it reduces the poisoning effects that occur at low reaction temperatures. The sulfated catalyst with the stable Fe-2(SO4)(3) species can be in situ regenerated through NH3 reduction followed by thermal treatment. Remarkably, compared with the fresh catalyst, the regenerated catalyst exhibited equivalent surface/ redox properties and the consequent catalytic performance.