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

Abstract

A fundamental understanding of the effect of SO 2 on low-temperature NH 3 -SCR is vitally important for SO 2 -tolerant catalysts. Here, the effects of SO 2 on CeO 2 , γ-Fe 2 O 3 , and γ-MnO 2 were reported, and the mechanism was thoroughly elucidated. Based on the experimental and density functional theory study, it was discovered that the NH 3 -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 CeO 2 and γ-Fe 2 O 3 , corresponding metal sulfates governed their denitrification efficiency when facing SO 2 intrusion, favored by the equilibrium between deposition and consumption of surface ammonium bisulfate. However, the activity of γ-MnO 2 , hardly affected by the formed manganese sulfate, was mainly encroached by a large amount of ABS covering active sites. Meanwhile, NH 3 , 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-Fe 2 O 3 .

Facile H2O-Contributed O2Activation Strategy over Mn-Based SCR Catalysts to Counteract SO2Poisoning

“…This demonstrated that H 2 O tended to mitigate SO 2 deactivation under certain conditions. Subsequently, the deactivated catalysts were purged at 350 °C under a N 2 atmosphere for 1 h to remove ABS, 20 and the unusual effect of H 2 O could also be reflected. It can be seen that the low-temperature performance of Mn-NSO-R elevated from 30% to around 80% at 150 °C.…”

“…The thermal regeneration temperature came from the ABS decomposition condition reported in our previous work. 20 MnO x was prepared by thermal decomposition of MnC 2 O 4 at 400 °C for 2 h in air.…”

“…19 It can be continuously deactivated by the persistent deposition of NH 4 HSO 4 (ammonium bisulfate, ABS) and sulfation of Mn active sites. 20 Although the surface acidity of catalysts may be enhanced accordingly, 21 poisoned catalysts generally show poorer activity due to diminished reactive oxygen species (ROS), which results in restricted electron transport and oxygen mobility. 22 Herein, γ-MnO 2 was employed as a model catalyst to explore the influence of H 2 O on SCR performance in a sulfurcontaining atmosphere.…”

“…Mn-based catalysts have been considered some of the most effective materials to catalyze a NO removal reaction at low temperatures due to the variable valence states and excellent redox properties even as single manganese oxide catalysts. , However, the satisfying catalytic performance of Mn-based catalysts is vulnerable to the attack of SO 2 in practical application . It can be continuously deactivated by the persistent deposition of NH 4 HSO 4 (ammonium bisulfate, ABS) and sulfation of Mn active sites . Although the surface acidity of catalysts may be enhanced accordingly, poisoned catalysts generally show poorer activity due to diminished reactive oxygen species (ROS), which results in restricted electron transport and oxygen mobility …”

“…Surface Species Concentration and Surface Adsorption Capacity a,b of the high oxidation state (Mn 4+ ) by SO 2 10,20. Yu et al reported that the peak around 645.1 eV in Mn 2p 3/2 spectra reflected the formation of MnSO 4 (Mn 2+…”