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

Abstract

The development of Fe-based catalysts for the selective catalytic reduction of NO x by NH 3 (NH 3 −SCR of NO x ) has garnered significant attention due to their exceptional SO 2 resistance. However, the influence of different sulfur-containing species (e.g., ferric sulfates and ammonium sulfates) on the NH 3 − SCR activity of Fe-based catalysts as well as its dependence on exposed crystal facets of Fe 2 O 3 has not been revealed. This work disclosed that nanorod-like α-Fe 2 O 3 (Fe 2 O 3 −NR) predominantly exposing (110) facet performed better than nanosheet-like α-Fe 2 O 3 (Fe 2 O 3 −NS) predominantly exposing (001) facet in NH 3 −SCR reaction, due to the advantages of Fe 2 O 3 −NR in redox properties and surface acidity. Furthermore, the results of the SO 2 /H 2 O resistance test at a critical temperature of 250 °C, catalytic performance evaluations on Fe 2 O 3 −NR and Fe 2 O 3 −NS sulfated by SO 2 + O 2 or deposited with NH 4 HSO 4 (ABS), and systematic characterization revealed that the reactivity of ammonium sulfates on Fe 2 O 3 catalysts to NO(+O 2 ) contributed to their improved catalytic performance, while ferric sulfates showed enhancing and inhibiting effects on NH 3 −SCR activity on Fe 2 O 3 −NR and Fe 2 O 3 −NS, respectively; despite this, Fe 2 O 3 −NR showed higher affinity for SO 2 + O 2 . This work set a milestone in understanding the NH 3 −SCR reaction on Fe 2 O 3 catalysts in the presence of SO 2 from the aspect of crystal facet engineering.