DFT studies of elemental mercury oxidation mechanism by gaseous advanced oxidation method: Co-interaction with H₂O₂ on Fe₃O₄ (111) surface

Highlights: • Electron transfer occurred from Hg⁰ to the produced OH species. • Hg⁰ possible oxidation intermediates during the processes were compared. • The major reaction pathway of Hg oxidation products on the surface was discussed. - Abstract: Density functional theory calculations have been carried out for H₂O₂ and Hg⁰ co-interaction on Fe₃O₄ (111) surface. On the Fe_tet1-terminated Fe₃O₄ (111) surface, the most favored configurations are H₂O₂ decomposition and produce two OH groups, which have strong interaction with Hg atom to form an OH−Hg−OH intermediate. The adsorbed OH−Hg−OH is stable and hardly detaches from the catalyst surface due to the highly endothermic process. A large amount of electron transfer has been found from Hg to the produced OH groups and has little irreversible effect on the Fe₃O₄ (111) surface. On the Fe_oct2-terminated Fe₃O₄ (111) surface, the Fe_oct2 site is more active than Fe_tet1 site. H₂O₂ decomposition and Hg⁰ oxidation processes are more likely to occur due to that the Fe_oct2 site both contains Fe²⁺ and Fe³⁺ cations. The calculations reveal that Hg⁰ oxidation by the OH radical produced from H₂O₂ is energetically favored. Additionally, Hg⁰ and H₂O₂ co-interaction mechanism on the Fe₃O₄ (111) interface has been investigated on the basis of partial local density of state calculation.