d-π Orbital Interaction Promoting NO_<i>x</i> Selective Reduction on the Mn-Doped α-Fe₂O₃(001) Catalyst

Understanding the structure-activity relationship on a solid surface is crucial for developing an efficient low-temperature NH₃-SCR catalyst. Herein, an in-depth investigation was conducted on a single-atom Mn-doped α-Fe₂O₃ catalyst by combining experimental studies and density functional theory calculations. Mn doping not only facilitates N-H cleavage in the Eley-Rideal (E-R) pathway but also promotes the adsorption of NO and the cleavage of the N-O bond, lowering the energy barrier of the rate-determining step in the Langmuir-Hinshelwood (L-H) pathway. Thus, Mn doping facilitates the catalytic reaction along both potential pathways, which promotes the NH₃-SCR reaction. Further analysis reveals that the doping of Mn introduces an unoccupied d_<i>xy</i> orbital, which facilitates the interaction with the π orbital of NO, thereby augmenting NO adsorption. Moreover, Mn doping redistributes the electron density, enhancing the flexibility of electrons on the Fe atom and facilitating electron transfer from Fe to the π* orbital of Mn-N-O, thus promoting N-O cleavage. The present study demonstrates that the incorporation of unoccupied d orbitals with appropriate energy and symmetry facilitates a d-π interaction between the dopant and reactant, thereby significantly enhancing catalytic efficiency. These findings provide valuable new insights into the design of high-performance NH₃-SCR catalysts.