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

Ceria (CeO2) based catalysts have been widely reported as potential materials for elemental mercury (Hg-0) oxidation in flue gas. However, the effect of sulfur dioxide (SO2) and water vapor (H2O) on Hg-0 adsorption over CeO2, which is critical for subsequent Hg-0 oxidation are still unclear. The detail reaction mechanisms involved in Hg-0 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 Hg-0 on the CeO2(1 1 1) surface. H2O leaned to bond with surface Ce atoms. The inhibitive impact of H2O on Hg-0 adsorption was ascribed to the following two reasons: 1) H2O competed with Hg-0 for active sites; 2) H2O dissociatively adsorbed on CeO2 surface to generate Ce-OH group, and hence occupied the lattice oxygen on catalyst surface.