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 NOx by NH3 (NH3–SCR of NOx) 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.