Tuning the Fe–N4 electrocatalytic CH3NO2 reduction reaction based on axial ligands: A computational study

Amine compounds, which serve as crucial chemical materials, have extensive applications in the fields of agricultural chemicals, pharmaceuticals, and fine chemicals. The hydrogenation of nitro compounds to produce amine compounds in industry generally requires high-temperature and high-pressure conditions, resulting in energy loss and the emission of pollutants. However, the electrocatalytic reduction synthesis of amines represents a green and environmentally friendly reaction method. In this study, the mechanism by which the Fe–N4 electrocatalytic nitromethane (CH3NO2) was hydrogenated to methylamine (CH3NH2) was systematically studied using density functional theory. The adsorption of CH3NO2 was identified as the rate-determining step in the elementary process. Then, 17 types of axial ligands were coordinated in the z-direction of the Fe–N4 active site, and their effects on the Fe–N4 geometry, charge population, and adsorption strength of intermediates during CH3NO2 reduction were studied. The results indicated that CN−, NC−, and OH− can effectively enhance the activation of CH3NO2 through the Fe–N4 active site. Furthermore, the role of axial ligands in tuning the catalytic performance of the catalyst was studied at the atomic orbital level. The correlation between the d-band center and the rate-determining step free energy is a volcanic curve, and the electrocatalytic amine reduction reaction of catalysts performance is predicted by the d-band center as a descriptor.