Controlling morphology and doping tungsten to regulate sulfur species on molybdenum disulfide for removing Hg⁰ from flue gas

Molybdenum disulfide (MoS₂) is considered a favorable absorbent for removing heavy metals. However, due to its various morphologies, MoS₂ exhibits significant differences in its performance for removing mercury from flue gas. In the present study, the flower-like, spherical MoS₂ and W-MoS₂ were prepared by regulating the interlayer spacing and doping tungsten (W) in MoS₂ for removing gaseous mercury (Hg⁰). The results show that the number of active sulfur sites (S^2- and S₂^2-) was critical to the adsorption performance of MoS₂ for Hg⁰. The flower-like MoS₂ demonstrated optimum properties below 125°C which attributed to the presence of dominated S^2- sites, while spherical MoS₂ and W-MoS₂ showed a wider application temperature range (up to 175°C) during Hg⁰ removal which attributed to the unsaturated sulfur S₂^2- and active oxygen. In terms of the mechanism, Hg⁰ is directly inserted into the Mo-S bond of MoS₂ to form a transition state [Hg·Mo]-S, and then the original Mo-S is interrupted to form a new β-Hg-S bond, or combine with surface oxidation to form HgO. The oxygen in the flue gas can supplement the surface active oxygen on the MoS₂, which enables the circulation of Mo⁵⁺. Hg⁰ also reacted with S₂^2- to form α-HgS.