Theoretical insight into the influence of SO2 on the adsorption and oxidation of mercury over the MnO2 surface
Shibo Zhang, Juan Dang, Mercedes Dı́az-Somoano, Qingzhu Zhang
Abstract
The inferior sulfur resistance is a major technical bottleneck of Mn-based catalysts to be employed as low-temperature selective catalytic reduction (SCR) catalyst for elemental mercury (Hg 0 ) oxidation. The first-principle calculation based on density functional theory was adopted to investigate the influence of SO 2 on mercury adsorption and oxidation over the MnO 2 surface. The results indicated that Hg 0 preferred to adsorb at the hollow and O br bridge sites on the surface, and the adsorption of HgO was a strong chemisorption behavior. SO 2 could be retained on the MnO 2 surface through chemisorption. The adsorbed SO 2 generated inhibition on Hg 0 adsorption by the competitive and repulsive effects, while the effect of SO 2 on HgO adsorption was negligible. SO 2 showed almost no impact on the adsorption and dissociation of O 2 . Hg 0 adsorption and oxidation at the active sites adjacent to the adsorbed SO 2 was apparently restrained on the SO 2 -covered surface, and the desorption of generated HgO became easier compared to that on the clean surface. By contrast, Hg 0 oxidation at the nonadjacent sites to SO 2 was little influenced by the adsorbed SO 2 . The study results would offer guidance for impairing the inhibitory effect of SO 2 and improving the SO 2 resistance of Mn-based catalysts.