NOx removal performance and sulfur poisoning mechanism of Fe-doped Mn-based spinel catalysts in low-temperature NH3-SCR

Abstract

Nitrogen oxides (NO_x), from industrial exhaust and motor vehicles, are major atmospheric pollutants, yet their efficient removal via low-temperature NH₃-SCR is severely hampered by SO₂-induced catalyst poisoning. Here we demonstrate that Fe-doped Mn₃O₄ spinel (Fe_0.8Mn_2.2O₄) achieves exceptional SO₂ resistance through a synergistic dual mechanism that fundamentally reconstructs both the reaction and deactivation pathways: (1) sacrificial sulfation – Fe sites preferentially form labile FeSO₄, protecting Mn active sites from permanent poisoning; and (2) reaction pathway regulation-Fe doping promotes gaseous NO₂ formation and introduces Brønsted acid sites, shifting the dominant SCR pathway from Langmuir–Hinshelwood (L–H) to Eley–Rideal (E–R). This E–R route minimizes direct competition with SO₂ for adsorption sites, conferring intrinsic sulfur tolerance. The catalyst maintains >90% NO_x conversion at 80–300 °C and retains >80% activity after prolonged SO₂ exposure at 120 °C. Moreover, the modulated surface acidity and controlled intermediate turnover suppress N₂O formation, significantly enhancing N₂ selectivity. This work provides deeper insight into the role of Fe doping in Mn-based catalysts, elucidating how it confers sulfur resistance through preferential sulfation and reaction pathway modulation.