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 (S2- and S22-) 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 S2- 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 S22- 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 S22- to form α-HgS.