Reaction Pathways of the Selective Catalytic Reduction of NO with NH₃ on the α-Fe₂O₃(012) Surface: a Combined Experimental and DFT Study

Fe₂O₃-based catalysts have promising potential in the selective catalytic reduction (SCR) of NO with NH₃ with the advantages of environmental friendliness, excellent medium-high SCR activity, good N₂ selectivity, and high SO₂ tolerance. However, the NH₃-SCR mechanism over Fe₂O₃-based catalysts remains highly uncertain and controversial due to the complex nature of the SCR reaction. Herein, the NH₃-SCR reaction pathways over the α-Fe₂O₃(012) surface are elucidated at the atomic level by density functional theory calculations and experimental measurements. We demonstrate that, different from the NH₃ activation mechanism in numerous SCR catalytic systems, the reaction tends to follow the NO activation mechanism, in which NO activated at Fe sites reacts with NH₃ to form a NH₂NO intermediate and further decomposes into N₂ and H₂O, in synchronization with the formation of a surface OH group. Subsequently, the catalyst is regenerated by an O₂-assisted surface-dehydrogenation process. The activation of NO as well as the formation of the NH₂NO intermediate is the rate-determining step of the complete SCR cycle. This study enhances the atomic-level understanding toward the NH₃-SCR reaction and provides insights for the development of Fe₂O₃-based SCR catalysts.