Enhancing synergistic removal of gaseous mercury by low-valence sulfur engineered V₂O₅-WS₂/TiO₂ SCR catalysts

Elemental mercury (Hg⁰) is the dominant species in coal-fired flue gas, posing significant environmental hazards due to its volatility and persistence. Conventional V₂O₅-based selective catalytic reduction (SCR) catalysts exhibit limited Hg⁰ oxidation capacity (<50%) under low-temperature and SO₂-rich conditions. In this study, a novel low-valence sulfur-engineered V₂O₅-WS₂(tungsten disulfide; W = tungsten)/TiO₂ catalyst is developed to enhance synergistic Hg⁰ removal through complementary oxidation and fixation pathways. Compared to V₂O₅/TiO₂ and V₂O₅-WO₃/TiO₂, the V₂O₅-WS₂/TiO₂ catalyst achieves a superior Hg⁰ oxidation efficiency of 70.27% at 200 °C. This result is mainly enabled by an optimized distribution of surface oxygen species (O_α), accelerated redox cycling (V⁵⁺/V⁴⁺), and a strong S-Hg affinity that promotes stable HgS formation. Comprehensive characterization indicates that WS₂ incorporation suppresses Brønsted acidity while enriching Lewis acid sites. It also enhances oxygen mobility, stabilizes terminal V=O species, and introduces S^2- sites that are crucial for Hg⁰ fixation. Under a simulated SCR flue-gas matrix, NO and NH₃ help preserve and regenerate active sites. They also promote in situ NO₂ formation, which further enhances Hg⁰ oxidation. Although SO₂ increases Hg⁰ uptake through surface sulfate formation, it simultaneously consumes active oxygen and blocks redox sites, diminishing oxidation efficiency. This study elucidates a coupled mechanism of redox-driven oxidation and sulfur-assisted fixation over V₂O₅-WS₂/TiO₂, providing a viable design strategy for SO₂-tolerant, high-efficiency Hg control catalysts in coal-fired power applications.