Reaction Pathway and Kinetic Origin of Low-Temperature NH3 -SCR over a Mn-Cu Dual-Atom Catalyst: A DFT Study

Abstract

The reaction mechanism of NH3-SCR over a Mn–Cu dual-atom catalyst was investigated by combining density functional theory (DFT) calculations with microkinetic analysis. The catalyst is modelled as isolated Mn and Cu atoms anchored on N-doped graphene. The adsorption characteristics of reactant species involved in the NH3-SCR reaction were systematically examined, and multiple possible NH3-SCR reaction pathways were proposed and evaluated. The most favourable reaction pathway involves the co-adsorption of NO2 and NH3 on the Mn–Cu/NG catalyst surface, followed by their interaction to form H2O and the *NHNO intermediate. Subsequently, the *NHNO intermediate reacts with gaseous NO to generate NO2 and the *NNH intermediate, and finally, N2 is produced through the dehydrogenation of the *NNH intermediate. Electron transfer between Mn and Cu atoms enhances gas adsorption on the catalyst surface. The participation of NO2 in the NH3-SCR reaction facilitates the fast NH3-SCR pathway. In addition, strong electron transfer occurs between adsorbed NO2 and the Mn–Cu/NG catalyst, leading to the activation of NO2 and resulting in a relatively low energy barrier of 1.23 eV. Owing to its relatively low activation energy of 0.80 eV, the Mn–Cu/NG catalyst exhibits a suitable operating temperature window of 400 – 670 K. However, the proposed Mn-Cu/NG catalyst is intended for low-temperature NH3–SCR applications to minimize potential oxidation of the graphene support.