Density Functional Theory Study On The Adsorption Of Mercury In Coal-fired Flue Gas On The Surface Of Mn/Fe₃O₄(111)

Sorbent injection,catalytic oxidation and many other methods have been applied for mercury control in the flue gas.Due to the high cost,secondary pollution and non-recycling of these methods,the search for more cost-effective mercury removal methods has never been stopped.(Fe_3-xMn_x)_1-?O₄was found as a kind of promising material to enhance the adsorption capability of Hg⁰.By taking advantage of Mn-Fe spinel catalyst with low-temperature oxidation,Mn-Fe spinel can be injected before Wet Electrical Dust Precipitator?WESP?for the removal of mercury and sulfur dioxide.However,previous research has paid less attention on mechanism studies on the mercury removal by Mn doped Fe₃O₄?111?surface,which is equally important for the modification of catalysts.Based on the above backgroud,density functional theory?DFT?was employed to investigate the mechanisms in molecule interaction on pure magnetite surfaces and Mn doped surfaces in this study,This study intends to reveal the reaction mechanism of different mercury species on Fe₃O₄?111?and Mn doped Fe₃O₄?111?surface through different adsorption sites,adsorption energy,Mulliken charge,charge transfer,and density of states.To begin,start with the adsorption of mercury in different forms on Fe₃O₄?111?surface.The development of stable structures of Hg⁰,HgCl and HgCl₂ on the surface were obtained.The results of quantum chemical calculation showed that Hg⁰ was mainly physically bound to the Fe₃O₄?111?surface yielding adsorption energy around-30 k J/mol.HgCl and HgCl₂ were both adsorbed on Fe₃O₄?111?surface by the complete dissociation into a single Hg or Cl atom.The whole adsorption process was exothermic.The adsorption energies were-316.9 and-306.7 k J/mol,respectively.The formation of new Fe bonds was likely to account for high adsorption energies of HgCl and HgCl₂ on Fe₃O₄?111 1?surface.The adsorption of mercury in different forms on Mn/Fe₃O₄?111?surface was studied in the second place.Analogously,the laws of Hg⁰,HgCl and HgCl₂adsorption on Mn/Fe₃O₄?111?surface were obtained by quantum chemistry calculation.It was found that mercury atoms were adsorbed weakly chemically on Mn/Fe₃O₄?111?surfaces with the energy of-42.4 k J/mol.The energy barriers of Hg⁰ potential oxidation on Mn doped Fe₃O₄?111?surface were 262.4 and 306.8k J/mol.Distances of Hg-Cl bonds of HgCl and HgCl₂ molecules were lengthed and then broke into two or three atoms adsorption on the transition metals sites through an exothermic process.Chemisorption was likely to clarify the adsorption mechanism of HgCl and HgCl₂ yielding adsorption energies of-306.7 and-371.2 k J/mol respectively.The formation of new Cl-Mn/Fe bonds might be favorable for the high adsorption energies of HgCl and HgCl₂ on both surfaces.In addition,in order to reveal the influence of HCl components on the removal of Hg⁰ from coal-fired flue gas,the co-interaction of HCl and Hg⁰ on Mn/Fe₃O₄?111?surface was carried out.With the existence of HCl,the adsorption of Hg⁰ on the Mn doped Fe₃O₄?111?surface changed little.HCl and Hg⁰ were chemically adsorbed on the surface and the reaction pathway follows the Langmuir-Hinshelwood.This subject reveals the adsorption mechanism of Hg⁰,HgCl and HgCl₂ on the Mn/Fe₃O₄?111?surface,which lays a theoretical foundation for the subsequent application of Mn-Fe spinel.The results are of great significance for understanding the adsorption mechanism and guiding the design of adsorbents.