Boosting elemental mercury capture via an iodine-mediated pathway over a ternary BiOI-MnOx-TiO2 catalyst

Abstract

Elemental mercury (Hg⁰) emission from coal combustion flue gas poses significant environmental and health risks due to its high volatility, persistence, and toxicity. In this study, a novel ternary BiOI-MnO_x-TiO₂ (BiMnTi) composite catalyst was successfully synthesized via a simple three-step method for efficient Hg⁰ removal under dark conditions. The composite catalysts were characterized by SEM-EDS, HRTEM, XRD, H₂-TPR, N₂ adsorption–desorption, FTIR, XPS, and EPR. The BiOI-MnO_x-TiO₂ composite exhibited superior Hg⁰ removal efficiency (>97%) over a wide temperature range of 50–200 °C, and showed excellent resistance to SO₂ and NO poisoning. Characterization results confirmed that the introduction of BiOI effectively increased the proportion of Mn⁴⁺ content and surface chemisorbed oxygen (O_β) and promoted the formation of oxygen vacancies. XPS and H₂-TPR analyses further demonstrated enhanced electron transfer between BiOI and MnO_x-TiO₂, as well as improved redox properties. Mechanistic studies revealed that the synergistic interaction between BiOI and MnO_x-TiO₂ facilitated electron transfer at the interface, promoting the oxidation of I⁻ to active iodine species, which subsequently reacted with adsorbed Hg⁰ to form stable HgI₂. This work provides a promising strategy for designing efficient and sulfur-resistant catalysts for Hg⁰ removal in non-photocatalytic environments.