Theoretical insight into the influence of SO2 on the adsorption and oxidation of mercury over the MnO2 surface

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 (Hg0) oxidation. The first-principle calculation based on density functional theory was adopted to investigate the influence of SO2 on mercury adsorption and oxidation over the MnO2 surface. The results indicated that Hg0 preferred to adsorb at the hollow and Obr bridge sites on the surface, and the adsorption of HgO was a strong chemisorption behavior. SO2 could be retained on the MnO2 surface through chemisorption. The adsorbed SO2 generated inhibition on Hg0 adsorption by the competitive and repulsive effects, while the effect of SO2 on HgO adsorption was negligible. SO2 showed almost no impact on the adsorption and dissociation of O2. Hg0 adsorption and oxidation at the active sites adjacent to the adsorbed SO2 was apparently restrained on the SO2-covered surface, and the desorption of generated HgO became easier compared to that on the clean surface. By contrast, Hg0 oxidation at the nonadjacent sites to SO2 was little influenced by the adsorbed SO2. The study results would offer guidance for impairing the inhibitory effect of SO2 and improving the SO2 resistance of Mn-based catalysts.