Insights into the mitigation effect of water on SO₂ poisoning of a novel Mn-Fe oxide catalyst applied for low-temperature selective catalytic reduction of NO_x with NH₃

A novel Mn-Fe oxide catalyst (MnO_x@FeO_y) was synthesized by a one-pot method combining seed-mediated growth with galvanic replacement and applied for low-temperature NH₃-SCR of NO_x. The catalyst displayed superior tolerance towards H₂O + SO₂ compared to other Mn-Fe oxide catalysts prepared by the citric acid method (MnFeO_x-CA) and a solvothermal method (MnFeO_x-H) as less MnSO₄ and (NH₄)₂SO₄/NH₄HSO₄ were formed on the surface of the MnO_x@FeO_y catalyst after the combined H₂O + SO₂ exposure, primarily due to an inhibitory effect of H₂O on the oxidation of SO₂ on Mn sites. Thus, the H₂O provided protection to the Mn sites which resulting in improved H₂O + SO₂ resistance of the MnO_x@FeO_y catalyst. The study provides important new insight on how the adsorption of SO₂ on catalytically active Mn sites can be impeded to prevent fast catalyst deactivation of Mn-based NH₃-SCR catalysts.