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.