Unraveling the Effect of Mo Dopant in Fe2O3 Catalyst for Selective Catalytic Reduction of Nitric Oxide with NH3

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 N-2 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 N-2 formation at lower temperatures, as demonstrated in the literature. The calculated turnover frequency (TOF) of 1.9 x 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.