Enhancing Elemental Mercury Removal in Coal Combustion Flue-Gas over V2O5/TiO2-Based Catalysts via Coupled Oxidation and Sulfur-Assisted Fixation

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 Oα/Oβ 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.