Unraveling the SO2 Poisoning Effect over the Lifetime of MeOx (Me = Ce, Fe, Mn) Catalysts in Low-Temperature NH3-SCR: Interaction of Reaction Atmosphere with Surface Species

A fundamental understanding of the effect of SO2 on low-temperature NH3-SCR is vitally important for SO2-tolerant catalysts. Here, the effects of SO2 on CeO2, γ-Fe2O3, and γ-MnO2 were reported, and the mechanism was thoroughly elucidated. Based on the experimental and density functional theory study, it was discovered that the NH3-SCR performance of different metal oxide catalysts in a sulfur-containing atmosphere was closely related to the difference in the deposition/decomposition ability of the formed sulfate species. For CeO2 and γ-Fe2O3, corresponding metal sulfates governed their denitrification efficiency when facing SO2 intrusion, favored by the equilibrium between deposition and consumption of surface ammonium bisulfate. However, the activity of γ-MnO2, hardly affected by the formed manganese sulfate, was mainly encroached by a large amount of ABS covering active sites. Meanwhile, NH3, the reducing agent in the gas phase, significantly boosted the decomposition of metal sulfates. Moreover, the most easily decomposed iron sulfate, thus, claimed responsibility for the long-lasting sulfur tolerance of γ-Fe2O3.