Modulating the Activity and SO2 Resistance of α-Fe2O3 Catalysts for NH3–SCR of NOx via Crystal Facet Engineering

The development of Fe-based catalysts for the selective catalytic reduction of NO_x by NH₃ (NH₃-SCR of NO_x) has garnered significant attention due to their exceptional SO₂ resistance. However, the influence of different sulfur-containing species (e.g., ferric sulfates and ammonium sulfates) on the NH₃-SCR activity of Fe-based catalysts as well as its dependence on exposed crystal facets of Fe₂O₃ has not been revealed. This work disclosed that nanorod-like α-Fe₂O₃ (Fe₂O₃-NR) predominantly exposing (110) facet performed better than nanosheet-like α-Fe₂O₃ (Fe₂O₃-NS) predominantly exposing (001) facet in NH₃-SCR reaction, due to the advantages of Fe₂O₃-NR in redox properties and surface acidity. Furthermore, the results of the SO₂/H₂O resistance test at a critical temperature of 250 °C, catalytic performance evaluations on Fe₂O₃-NR and Fe₂O₃-NS sulfated by SO₂ + O₂ or deposited with NH₄HSO₄ (ABS), and systematic characterization revealed that the reactivity of ammonium sulfates on Fe₂O₃ catalysts to NO(+O₂) contributed to their improved catalytic performance, while ferric sulfates showed enhancing and inhibiting effects on NH₃-SCR activity on Fe₂O₃-NR and Fe₂O₃-NS, respectively; despite this, Fe₂O₃-NR showed higher affinity for SO₂ + O₂. This work set a milestone in understanding the NH₃-SCR reaction on Fe₂O₃ catalysts in the presence of SO₂ from the aspect of crystal facet engineering.