Unraveling the Effect of Mo Dopant in Fe₂O₃ Catalyst for Selective Catalytic Reduction of Nitric Oxide with NH

Understanding the catalyst design principles for the selective catalytic reduction (SCR) of NO is critical to developing processes for the treatment of combustion exhaust gases. In this context, density functional theory (DFT) simulations were employed to unravel the active site structure of Fe₂O₃-based catalysts, which have shown promise for NO SCR. Additionally, a detailed mechanistic investigation of the NO SCR reaction network with NH₃ on pristine and Mo-doped Fe₂O₃ surfaces was done to identify structure–activity relations. On Fe₂O₃, NO was oxidized to NO₂, which coupled with NH₂ to form an NH₂NO₂ intermediate. The N–O bond cleavage in the NHNO intermediate had a high barrier of 2.58 eV, and the formation of N₂O was energetically favorable, explaining the very low activity and low N₂ selectivity on the Fe₂O₃. Mechanistic shifts on the Mo-doped Fe₂O₃ catalyst avoided the NO oxidation and facilitated facile N–O bond cleavage in the NHNO intermediate, in a reaction pathway where the highest activation barrier was only 1.44 eV. This explains selective N₂ formation at lower temperatures, as demonstrated in the literature. The calculated turnover frequency (TOF) of 1.9 × 10–³ s–¹ matched the experimental TOF, validating the proposed reaction network and energy profile. The altered Lewis acidity and reducibility of the surface due to Mo doping, which modulated the local electronic structure around the Fe sites, were responsible for the enhanced catalytic activity. Structure–activity insights from this study may guide the design of efficient NH₃ SCR catalysts to meet the stringent emission norms for a NOₓ lean atmosphere.