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.

Coal-fired power plants equipped with selective catalytic reduction (SCR) and wet flue-gas desulfurization (WFGD) can co-control mercury, but performance is limited by incomplete upstream Hg⁰ oxidation and downstream re-emission. This study evaluated a 660 MW unit using gas-, liquid-, and solid-phase measurements and coordinated single-factor and coupled operating tests. Under baseline conditions, SCR Hg⁰ oxidation was 31.66%, WFGD Hg²⁺ capture was 73.79%, and net mercury removal was 31.08%, with a stack Hg^T concentration of 4.70 µg/Nm³. Coupled optimization increased SCR Hg⁰ oxidation to 69.76% and WFGD Hg²⁺ capture to 96.05%, reduced the re-emission index from 0.596 to 0.250, and raised net removal to 70.83%. SCR inlet temperature, equivalent space velocity, and catalyst health were the dominant upstream factors, while S(IV), oxidation–reduction potential (ORP), slurry pH, and oxidation air supply governed downstream stabilization. A practical operating window was identified near 340 °C, with a normalized stoichiometric ratio (NSR) of approximately 1.0, high ammonia injection uniformity, pH of 5.5–6.0, ORP of approximately 200 mV, and S(IV) of approximately 2 mmol/L. The results show that coordinated operation of existing SCR–WFGD equipment can substantially reduce stack mercury without dedicated mercury-control hardware, provided that NH₃ slip, SO₃-related risk, catalyst condition, and absorber stability are simultaneously constrained.

The efficient utilization of industrial waste (containing alkaline compounds, especially Ca-based species) for flue gas desulfurization (FGD) is of great importance for both environmental protection and resource recovery. In this study, paper industry white mud was modified with Ca(OH)₂ to develop a cost-effective sorbent with enhanced SO₂ removal performance. Optimization experiments identified the best preparation conditions as a 1:1 Ca(OH)₂/white mud ratio, 60 °C modification temperature, 6 h reaction time, and a liquid-to-solid ratio of 3:1. Under these conditions, the sorbent achieved nearly 100% SO₂ removal in the first 6 h and maintained >90% efficiency after 10 h, significantly outperforming raw white mud and Ca(OH)₂ alone. Characterization revealed that the superior performance originated from structural stability and abundant active sites. BET analysis showed a high surface area (24.8 m²·g⁻¹) and pore volume (0.160 cm³·g⁻¹), which were largely preserved after desulfurization, indicating resistance to pore blockage. SEM images confirmed a transition from porous aggregates to densified product layers, consistent with a shrinking-core/product-layer mechanism. XRD identified CaSO₄·2H₂O as the dominant product, while in situ FTIR demonstrated that O₂ promotes sulfite oxidation and H₂O accelerates hydrated sulfate formation, enhancing activity but causing faster pore blocking. The presence of NO extended sorbent durability by catalyzing continuous sulfite oxidation through NO/NO₂ redox cycling. Overall, Ca(OH)₂-modified white mud combines high reactivity, durability, and structural stability, offering a promising alternative to conventional sorbents. This work provides a viable route for the resource utilization of paper industry waste and practical insights for designing efficient and sustainable materials for industrial FGD systems.