Mechanisms of Elemental Mercury Transformation on α-Fe2O3(001) Surface from Experimental and Theoretical Study: Influences of HCl, O2, and SO2.

The reaction mechanisms of a mixture gas of HCl, O2, and SO2 in Hg0 adsorption on α-Fe2O3(001) surface are clarified by a group of adsorption experiments and theoretical calculations based on the density functional theory. The role of O2 in removing Hg0 is greatly influenced by the reaction temperature, meanwhile, the O atom coverage could affect the adsorption performance of Hg0. The dissociated O2 competes with the active sites of Cl species on Fe surface at low temperature, however, at medium temperature HCl and O2 could simultaneously facilitate the Hg0 transformation. Combined with the theoretical calculations, the role of SO2 and the probable pathways in removing Hg0 are discussed. Lower concentration of SO2 as well as HCl could dissociate on α-Fe2O3(001) surface, and the intermediates combine with gaseous Hg0, forming mercury-sulfur, mercury-chlorine compounds, and so forth. In addition, the different concentrations of SO2 are also discussed, and the corresponding X-ray photoelectron spectroscopy analysis on contrasted samples is conducted to research the morphological characterization, providing a reliable basis for judging the probable pathways of Hg0 transformation.

DFT and Experimental Study on the Mechanism of Elemental Mercury Capture in the Presence of HCl on α-Fe2O3(001).

To investigate the mechanism of Hg(0) adsorption on the α-Fe2O3(001) surface in the presence of HCl, which is considered to be beneficial for Hg(0) removal, theoretical calculations based on density functional theory as well as corresponding experiments are carried out. HCl adsorption is first performed on the α-Fe2O3(001) surface, and the Hg(0) adsorption on HCl-adsorbed α-Fe2O3(001) surface is subsequently researched, demonstrating that HCl dissociates on the surface of α-Fe2O3, improving the Hg(0) adsorption reactivity. With further chlorination of the α-Fe2O3(001) surface, FeCl3 can be achieved and the adsorption energy of Hg(0) on the FeCl3 surface reaches -104.2 kJ/mol, representing strong chemisorption. Meanwhile, a group of designed experiments, including Hg(0) adsorption on HCl-preadsorbed α-Fe2O3 as well as the coadsorption of both gaseous components, are respectively performed to explore the pathways of Hg(0) transformation. Combining computational and experimental results together, the Eley-Rideal mechanism with HCl preadsorption can be determined. In addition, subsequent X-ray photoelectron spectroscopy analysis verifies the appearance of Cl species and oxidized mercury, exhibiting the consistency with experiments.