Graphene-like MoS₂ containing adsorbents for Hg⁰ capture at coal-fired power plants

This research focuses on the development of a novel graphene-like MoS₂ containing adsorbent for the control of mercury emissions at coal-fired power stations in order to meet the ever-tightening environmental regulations. It was found that the adsorbent loaded with 5 wt% Mo demonstrated the best performance in Hg⁰ capture at low temperatures under different conditions such as space velocity and gas atmosphere etc. The variation in mercury concentration in flue gas due to Hg⁰ re-emission in FGD unit as well as the possible change in the performance of adsorbents after regeneration were also studied. Both experimental and theoretical studies were carried out to reveal the mechanism for mercury removal. It was found that the high Hg⁰ removal efficiency of the adsorbent with 5 wt% Mo was associated with the high sulphurization ratio of the precursors and the formation of graphene-like MoS₂ nanosheets with just a few atomic layers. Moreover, a DFT-D model with periodical slab calculation was established to illustrate the interactions between the Hg⁰ atoms and the MoS₂ (0 0 1) surface. The results showed that Hg⁰ atoms are chemically adsorbed on the MoS₂ nanosheets and the most favourable adsorption site is the T_Mo position. The adsorption pathways and energy profiles, obtained through the DFT study, further elucidated that the low energy barrier for Hg atoms to be adsorbed on the MoS₂ nanosheets allows low temperature adsorption process to occur, which is consistent with our experimental observation. The outstanding performance of this MoS₂ containing adsorbent in Hg⁰ capture is attributed to the significant influence of d orbitals of the Mo atom and p orbitals of the S atom towards the Hg atom. It can be concluded that the adsorbent loaded with 5 wt% Mo showed great potential to be applied in coal-fired power plants for the removal of mercury as well as the recovery of mercury as a resource.