Mechanism of Ce-Modified Birnessite-MnO2 in Promoting SO2 Poisoning Resistance for Low-Temperature NH3-SCR

A desirable catalyst for efficiently controlling NO x emissions often demands excellent SO 2 poisoning resistance. Here, we introduced Ce to modify birnessite-MnO 2 to obtain a Ce-MnO 2 catalyst with excellent activity ( T 90 = 85 °C) for the selective catalytic reduction of NO with NH 3 (NH 3 -SCR) at low temperatures. Compared with the MnO 2 catalyst that was severely deactivated after poisoning, the Ce-MnO 2 catalyst showed a significant improvement in SO 2 resistance with the NO conversion slightly decreasing from 100 to 95% at 150 °C. Physicochemical characterizations combined with density functional theory calculations indicated that the sulfates formed on Mn species and Ce species played different roles in the SCR reaction. The SO 3 2– adsorbed on the surface of the MnO 2 catalyst can react with NH 3 to form ammonium sulfites, leading to the deactivation of the catalyst. However, the SO 4 2– from Ce 2 (SO 4 ) 3 on the sulfated Ce-MnO 2 catalyst existed as new adsorption sites of NH 4 +, thus providing this catalyst with more acid sites. In addition, SO 2 was preferentially adsorbed and oxidized on Ce species, thereby protecting the Mn active centers from sulfation and deactivation. This work reveals the mechanism of Ce in promoting SO 2 resistance over birnessite-MnO 2 from the perspective of sulfates.