Axial coordination engineering for single-atom catalysts in bifunctional oxidation of NO and mercury.

Coal-fired power plants are major emitters of nitrogen oxides (NO) and elemental mercury (Hg), both of which pose significant environmental and health risks. While wet flue gas desulfurization (WFGD) and electrostatic precipitators (ESP) are effective in removing oxidized mercury (Hg) and particulate-bound mercury (Hg), capturing volatile Hg remains a significant challenge. Catalytic oxidation is a promising approach to convert NO and Hg into their more easily captured oxidized forms (NO and Hg), highlighting the need for highly efficient catalysts. In this study, graphene-supported iron single-atom catalysts (Fe SACs) with various axial ligands were systematically investigated using density functional theory (DFT). Adsorption energies of O and NO, along with energy barriers for key oxidation steps, were calculated to evaluate catalytic performance. Among the ten FeN-X catalysts examined, FeN-Br exhibited the lowest reaction energy barriers, while FeN-HO showed the highest turnover frequency (TOF) for both NO and Hg oxidation under simulated flue gas conditions. These results demonstrate the importance of axial ligand coordination in tuning catalytic activity. This work offers theoretical insights for the rational design of high-performance SACs for pollutant control in coal-fired flue gas treatment systems.