Elemental mercury (Hg⁰) removal in coal combustion flue-gas over commercial V-based SCR catalysts is still limited by insufficient low-temperature activity and the complex interference of gas components. In this work, V₂O₅/TiO₂, V₂O₅⁻MoO₃/TiO₂, and V₂O₅⁻MoS₂/TiO₂ catalysts were comparatively investigated for Hg⁰ removal under simulated coal combustion flue-gas conditions. Among them, V₂O₅⁻MoS₂/TiO₂ exhibited the best performance over the whole temperature window of 200–400 °C, reaching a Hg⁰ removal efficiency of 73.3% at 200 °C, which was markedly higher than those of V₂O₅/TiO₂ and V₂O₅⁻MoO₃/TiO₂. Under multicomponent SCR atmospheres in coal-fired plants, the catalyst also showed the highest Hg⁰ oxidation efficiency of 72.9%, indicating that MoS₂ modification was more effective than oxide promotion in enhancing low-temperature mercury removal. XRD and FT-IR results showed that MoS₂ and vanadia were successfully incorporated onto TiO₂ as dispersed surface phases, while the MoS₂-modified catalyst exhibited a distinct and persistent terminal V=O feature, implying the formation of a coupled Mo-S-V interfacial environment. H₂-TPR and NH₃-TPD demonstrated that MoS₂ modification simultaneously stabilized the redox structure and moderated the surface acidity, suppressing excessively strong NH₃ retention while maintaining a tunable oxidation-active surface. XPS analysis further revealed atmosphere-dependent redistribution of O_α/O_β species, sulfur oxidation to SO₃²⁻/SO₄²⁻ species, and dynamic V⁵⁺/V⁴⁺ interconversion, confirming that MoS₂ acted not only as a sulfur-containing component but also as an interfacial electronic regulator. Post-reaction Hg 4f XPS showed that retained mercury mainly existed as Hg²⁺ species, while Hg-TPD indicated that MoS₂ modification provided a more diverse and thermally stable mercury-binding environment. These results demonstrate that Hg⁰ removal over V₂O₅⁻MoS₂/TiO₂ proceeds through oxidation-retention coupling rather than simple oxidation alone. The enhanced performance originates from the synergistic effects of active oxygen migration, vanadium redox cycling, sulfur-assisted stabilization, and interfacial Mo-S-V electronic coupling. This work provides a promising strategy for designing multifunctional SCR catalysts in coal-fired plants for efficient Hg⁰ control under practical coal combustion flue-gas conditions.

The effects of NO₂ and NH₃ on Hg⁰ oxidation under fast selective catalytic reduction conditions remain unclear. To address this problem, we performed density functional theory calculations on the V₂O₅/TiO₂(001) surface in four states: clean surface, surface covered by NH₃, surface covered by NO₂, and surface where species are co-adsorbed. On the clean surface, Hg⁰ interacts weakly with oxygen sites; the adsorption energies at terminal (O_t), bridging (O_b) and interfacial bridging (O_b′) oxygen sites are −12.31, −12.58, and −21.22 kcal mol⁻¹, respectively. Direct oxidation by lattice oxygen encounters high activation barriers, ranging from 146.817 to 184.529 kcal mol⁻¹. NH₃ hinders the capture of Hg⁰. Since NH₃ preferentially occupies the vanadium-related active sites, the interaction between Hg⁰ and the catalyst is weakened, and the adsorption energies become less negative, ranging from −11.84 to −11.04 kcal mol⁻¹. NO₂ shows the opposite effect. It strengthens Hg⁰ adsorption near V-centered regions and provides an alternative oxygen source for Hg⁰ oxidation. The NO₂-assisted oxygen-transfer pathways have lower calculated barriers, ranging from 74.581 to 108.545 kcal mol⁻¹. When NH₃ and NO₂ are co-adsorbed, the barrier increases to 113.326 kcal mol⁻¹. Even so, NO₂-derived oxygen provides a relatively lower-energy oxygen-transfer route than lattice oxygen among the pathways examined.