Optimizing SO ₂ –Promoted NO Oxidation over Single-Atom Catalysts via Activity Volcano Plot

Catalytic oxidation represents a predominant strategy for NO abatement. While SO2 has been recognized as a critical promoter of NO oxidation, the fundamental principles governing catalytic performance and robust descriptors for material selection remain inadequately explored. Herein, we investigate the catalytic oxidation of NO with HSO3 as the oxidant over transition metal single-atom catalysts (TM-N4–C, TM = V ∼ Zn) through density functional theory (DFT) calculations. For HSO3 generation, the energy barriers showed minimal variation among catalysts, providing an insufficient basis for screening. Thus, we focused on the critical HSO3-mediated NO oxidation step (HSO3 + NO → SO2 + HNO2). Using the Brønsted–Evans–Polanyi relationship and microkinetic modeling, we established HSO3 adsorption energy as a descriptor and constructed a catalytic activity volcano plot. Notably, through screening 3d-5d transition metal single-atom catalysts identified Co–N4–C as the most active catalyst, which exhibits an optimal balance between a moderate 0.42 eV energy barrier and weak 0.43 eV Co-SO2 interaction. Subsequently, fixed-bed experiments performed on the theoretically screened optimal catalyst (Co–N4–C) confirmed the significant promotional effect of SO2, demonstrating that appropriate SO2 concentrations effectively enhance NO oxidation via the HSO3-mediated pathway. This work elucidates the fundamental promotion mechanism of SO2 and establishes a descriptor-based framework for the rational design of high-performance NO oxidation catalysts.