Molecular Understanding of Heterogeneous Mercury Adsorption and Oxidation Mechanisms over the CuCl2/TiO2 Sorbent

CuCl2/TiO2 has been regarded as a highly promising sorbent to remove elemental mercury (Hg-0) from flue gas. The density functional theory and periodical model were used to demonstrate mercury adsorption, transformation, and desorption mechanisms over the CuCl2/TiO2 sorbent. The calculation results show that the chemisorption mechanism dominates Hg-0, HgCl, and HgCl2 adsorption processes. Hg-0 adsorption on the CuCl2/TiO2 surface is exothermic by 45.51 kJ/mol. Hg-0 is found to be adsorbed on the CuCl2/TiO2 surface via the strong interaction between Hg and Cu atoms. Electron accumulation and depletion play a crucial role in the strong interaction between the adsorbed Hg and CuCl2/TiO2 surface. The formation of HgCl2 undergoes four elementary reaction steps: Hg-0 -> Hg(ads)-> HgCl(ads)-> HgCl2(ads)-> HgCl2. The energy barriers of HgCl(ads) and HgCl2(ads) formation steps are approximately 108.08 and 22.88 kJ/mol, respectively. HgCl2 desorption from the CuCl2/TiO2 surface is the rate-limiting step of the whole Hg transformation process and needs a reaction heat of 346.21 kJ/mol.