Role of SO2 and H2O in the mercury adsorption on ceria surface: A DFT study

Abstract

Ceria (CeO2) based catalysts have been widely reported as potential materials for elemental mercury (Hg0) oxidation in flue gas. However, the effect of sulfur dioxide (SO2) and water vapor (H2O) on Hg0 adsorption over CeO2, which is critical for subsequent Hg0 oxidation are still unclear. The detail reaction mechanisms involved in Hg0 adsorption on CeO2(1 1 1) surface in the presence of SO2 and H2O were investigated with first-principles calculations based on density functional theory. The results suggest that SO2 was chemical adsorbed on CeO2(1 1 1) surface through S atom interacting with O top site. The adsorption energies and density of state indicate that SO2 interacted with the surface lattice oxygen of CeO2 to form a SO3-like species. The surface charge was redistributed during the formation of SO3, which promoted the adsorption of Hg0 on the CeO2(1 1 1) surface. H2O leaned to bond with surface Ce atoms. The inhibitive impact of H2O on Hg0 adsorption was ascribed to the following two reasons: 1) H2O competed with Hg0 for active sites; 2) H2O dissociatively adsorbed on CeO2 surface to generate Ce-OH group, and hence occupied the lattice oxygen on catalyst surface.