Synthesis of copper-nitrogen-carbon catalysts and the enhancement mechanism of mercury removal performance in coal-fired flue gas

BACKGROUND

Mercury pollution from coal-fired flue gas poses significant threats to human health and the ecosystem, prompting strict control measures under international conventions like the Minamata Convention. Existing flue gas treatment technologies (e.g., dust removal, desulfurization) have limited mercury removal efficiency, while activated carbon injection suffers from high costs and secondary treatment issues. Graphitic carbon nitride (g-C₃N₄) shows potential for mercury removal, and doping copper (Cu) atoms can enhance its performance. This study aimed to synthesize a Cu-N₄C catalyst via high-temperature calcination and explore its mercury removal mechanism in coal-fired flue gas.

RESULT

The Cu-N₄C catalyst prepared at 800 °C showed remarkable mercury removal performance, with an average conversion of 98.50% at 50 °C and almost no Hg⁰ release, significantly outperforming conventional g-C₃N₄. It maintained high efficiency under various flue gas components, demonstrating strong resistance to interference from O₂, CO₂, NO, and SO₂. Structural characterization by XRD and FTIR confirmed the high crystallinity of Cu-N₄C and the impact of Cu doping on its chemical bonds, while SEM/EDX revealed a fluffy porous structure with uniform Cu distribution. N₂ adsorption–desorption tests showed that Cu-N₄C had a large specific surface area of 232 m²/g and a mesoporous structure, which enhanced the contact area with mercury. Mechanistic studies via Hg-TPD and XPS indicated that Cu⁺ in Cu-N₄C was oxidized to Cu²⁺ during the reaction, forming a CuHg alloy with Hg⁰ to promote mercury removal through redox reactions and metal-mercury chemisorption.

CONCLUSION

This study developed a novel Cu-N₄C catalyst for efficient mercury removal from coal-fired flue gas. The catalyst showed superior performance at low temperatures (50 °C) and maintained stability in complex flue gas environments. The mechanism involves Cu⁺-mediated oxidation of Hg⁰ to Hg²⁺ and formation of a CuHg alloy. This work provides a new material option for industrial mercury removal and a theoretical basis for optimizing catalyst design. © 2025 Society of Chemical Industry (SCI).