Effect of SO3 on elemental mercury adsorption on a carbonaceous surface

► SO3 competes for the active sites on the carbonaceous surface and inhibits Hg adsorption. ► SO3 suppresses the activity of its next-nearest-neighbor carbon atom. ► SO3 cannot directly provide the active sites. ► SO3 decreases the unoccupied frontier molecular orbitals of the carbonaceous surface. ► SO3 increases the LUMO-HOMO energy gap of the carbonaceous surface.