Enhanced simultaneous oxidation of Hg⁰ and NO with SO₂ resistance by dual single-atom Co-Cu incorporated g-CN nanocomposites

The simultaneous catalytic oxidation of Hg-0 and NO within coal-fired plants is crucial in abating diverse pollutants. Nevertheless, conventional catalysts often encounter challenges, such as diminished oxidation efficiency at lower temperatures and competitive adsorption with other gaseous components, particularly SO2, to remove Hg-0 and NO. A nanocomposite catalyst, Co-Cu/g-CN, was developed to address these issues, featuring dual single-atom doping of Co and Cu in graphitized carbon nitride (g-CN). Surface characterization techniques and theoretical calculations confirmed that Co and Cu single atoms were successfully incorporated into the g-CN structure. Moreover, this innovative catalyst exhibited a strong metallic interaction between the dual single atoms, which led to an increased production number of superoxides (O-2(-)), albeit with a slightly reduced oxidizing ability. The trade-off in the active centers of O-2(-) ultimately enhanced the oxidation capability of Hg-0 and NO owing to the augmented number of O-2(-). Co-Cu/g-CN demonstrated complete Hg-0 removal efficiency and achieved 81.3% NO removal efficiency at 200-250 degrees C. Both theoretical analysis and DRIFTS investigation revealed that the competitive adsorption of SO2 over O-2(-) was significantly weakened due to the reduced oxidizing ability of O-2(-). Additionally, the Cu single atoms acted as sacrificial sites for sulfate species, thereby preserving the catalytic activity of Co single atoms for NO oxidation. This research provides a valuable dual single-atom-catalyst fabrication strategy for addressing flue-gas NOx and Hg-0 pollution.