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 (Oα), 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 S2- 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.