Theoretical study of mercury species adsorption mechanism on MnO2(1 1 0) surface

• Periodic DFT study on the Hg-species adsorption on MnO2 catalyst was performed.
• Hg0 is strongly adsorbed on the MnO2(1 1 0) surface with chemisorption mechanism.
• HgCl and HgCl2 form stable complexes on the MnO2(1 1 0) surface.
• The adsorption of Hg-species is favorable at low temperatures.

MnO2-based sorbents have been considered as potential materials for Hg removal due to their high adsorption ability and high activity in the catalytic oxidation of Hg in coal-fired flue gas. First-principles calculations based on the density functional theory and the periodic slab models were used to gain a fundamental understanding of mercury adsorption mechanism on MnO2(1 1 0) surface. The adsorption energies and adsorption structures of mercury species (Hg0, HgCl and HgCl2) on MnO2(1 1 0) surface were calculated. The electronic structural changes of surface system before and after adsorption were investigated to better understand the surface reactivity. The potential energy diagram of different pathways of mercury species adsorption on surface were given in order to elucidate the mechanism of adsorption process. In addition, thermodynamic data based on statistical thermodynamic partition functions for mercury species adsorption were also calculated. The results show that Hg0 is strongly adsorbed on MnO2(1 1 0) surface with chemisorption. The energy diagrams of HgCl and HgCl2 adsorption and possible desorption show that HgCl and HgCl2 can exist stably on the surface because the desorption and dissociation are highly endothermic, yet there is still a possibility that HgCl dissociates and Hg desorbs from the surface. The trends of equilibrium constant suggest that mercury species adsorptions on MnO2(1 1 0) surfaces are favorable at low temperature and HgCl2 is more easily captured than Hg0 under high temperature.