Charge-distribution modulation of copper ferrite spinel-type catalysts for highly efficient Hg0 oxidation

Highlights: • Charge distribution of copper ferrite catalysts was modulated for Hg⁰ oxidation. • CuFe₂O₄ catalyst showed > 90 % Hg° oxidation efficiency in a wide temperature window. • Hg⁰ oxidation by HCl over copper ferrite spinel followed the Eley-Rideal mechanism. • HgCl₂* formation was identified as the rate-limiting step of Hg⁰ oxidation. Hg⁰ catalytic oxidation is an attractive approach to reduce mercury emissions from industrial activities. However, the rational design of highly active catalysts remains a significant challenge. Herein, the charge distribution modulation strategy was proposed to design novel catalysts: copper ferrite spinel-type catalysts were developed by introducing Cu²⁺ cations into octahedral sites to form electron-transfer environment. The synthesized catalysts with spinel-type stoichiometry showed superior catalytic performance, and achieved > 90 % Hg⁰ oxidation efficiency in a wide operation temperature window of 150−300 °C. The superior catalytic performance was closely associated with the mobile-electron environment of copper ferrite. Hg⁰ oxidation by HCl over copper ferrite followed the Eley-Rideal mechanism, in which physically adsorbed Hg⁰ reacted with active chlorine species. Density functional theory calculations revealed that octahedral Cu atom is the most active site of Hg⁰ adsorption on copper ferrite surface. Both direct oxidation pathway (Hg* → HgCl₂*) and HgCl-mediated oxidation pathway (Hg* → HgCl* → HgCl₂*) played important role in Hg⁰ oxidation over copper ferrite. HgCl₂* formation was identified as the rate-limiting step of Hg⁰ oxidation. This work would provide a new perspective for the development of admirable catalysts with outstanding Hg⁰ oxidation performance.