Adsorption mechanism of elemental mercury (Hg0) on the surface of MnCl2 (1 1 0) studied by Density Functional Theory

Abstract

The objective of this research is to reveal the mechanism of effective and inexpensive sorbent MnCl2 for elemental mercury (Hg0) removal from the flue gas. The adsorption behavior of Hg0 on MnCl2 (110) surface was investigated theoretically using Density Functional Theory. The geometry optimization and adsorption energy of Hg0 on MnCl2 surface were calculated by generalized gradient approximation with Perdew−Burke−Ernzerh functional (GGA/PBE) and DNP basis. Results showed that Hg0 adsorption on MnCl2 (110) surface is chemisorption with adsorption energy of −156.620kJ/mol. According to Hirshfeld charge analysis, Hg0 has active interaction with Cl atoms (Cl-12, Cl-32, Cl-44) and Mn-40 atom on MnCl2 (110) surface. The partial density of states (PDOS) analysis further reveals that p- and d-orbitals of Cl atoms strongly hybridize with s- and d-orbitals of Hg atom. The d-orbital of Mn-40 also has essential interaction with Hg atom. Both of them contribute to the stable adsorption system of Hg0–MnCl2. The equilibrium constant decreases with the increase of temperature, which coincides with data for exothermic adsorption system. For the first time, this study investigated the mechanism of Hg0 adsorption on metal chloride surface using DFT method. It provides a significance theoretical support for metal chloride application in Hg0 adsorption and removal. The results obtained in this research are in good agreement with previous experiment. This method can be used to reveal Hg0 capture mechanism in some complex systems.