Sabatier-optimized co-incorporated CN catalysts for enhanced elemental mercury oxidation via an O₂-mediated...

Understanding the balance of oxygen activation and product desorption is a prerequisite for achieving high activity and durability in heterogeneous catalytic oxidation following the O₂-mediated Eley-Rideal (E-R) mechanism. Using catalytic oxidation of gaseous elemental mercury (Hg⁰) from coal-fired flue gas as a probe, we establish a Sabatier relationship for O₂-mediated E-R pathways over metal-incorporated graphitic carbon nitride (M-CN) catalysts. Density functional theory calculations reveal that the overall reaction rate is jointly limited by Hg-assisted O-O bond cleavage and the desorption of oxidized mercury species (HgO)_x. Correlating catalytic activity with atomic oxygen adsorption energies identifies Co-CN as optimally positioned near the apex of the Sabatier volcano among ten M-CN catalysts. Guided by this mechanistic insight, a Co-CN catalyst is rationally synthesized via a novel stepwise strategy and exhibits near-complete Hg⁰ removal at 280 °C, strong tolerance toward high SO₂ concentrations, and a synergistic promotional effect of NO, while maintaining an Hg⁰ removal efficiency of 85.13% after eight thermal regeneration cycles, demonstrating excellent operational stability and recyclability. Long-term dynamic tests reveal that Co-CN reaches a stable balance between Hg⁰ oxidation and product desorption after ∼15 h, delivering a Hg⁰ removal capacity of 0.94 mg⋅g^-1, superior to most reported carbon-based catalysts. Mechanistic validation confirms that Hg⁰ oxidation proceeds via surface-activated oxygen species on Co-N sites, while gradual accumulation of surface-bound (HgO)_x and partial Co-N oxidation dictate long-term performance decay under oxygen-rich conditions. This work establishes a fundamental framework for designing Sabatier optimal catalysts in O₂-mediated E-R models for environmental remediation.