Toward predicting the mercury removal by chlorine on the ZnO surface

Abstract

• HgCl 2 is directly formed by the adsorbed Cl and Hg 0 on the ZnO surface and not via HgCl intermediate. • The dissociated H atoms on the ZnO surface inhibit the formation of HgCl 2 . • Cl 2 rather than HCl is responsible for the oxidation of Hg 0 on the ZnO surface. • HgCl 2 is easy to be formed via the E–R and L–H mechanisms on the ZnO surface. The density functional theory with the generalized gradient approximation has been used to determine the binding mechanism of Cl 2 , HCl and Hg species on the ZnO( 1 0 1 ¯ 0 ) surface, and the Hg 0 oxidation mechanism by Cl 2 (or HCl) on the ZnO surface. Cl 2 and HCl are dissociatively adsorbed on the surface, and Cl atom bonds to two adjacent Zn atoms. Binding energy of Hg 0 is showing a physisorption mechanism, while HgCl 2 is strongly adsorbed on the surface in the molecularly mode, which indicates that the oxidation of Hg 0 is necessary for its removal from flue gas . HgCl is not an indispensable intermediate during the Hg 0 oxidation to form HgCl 2 . Three Hg 0 oxidation mechanisms have been investigated, and the HgCl 2 is easy to be formed via both the Eley–Rideal and Langmuir−Hinshelwood mechanisms, while Mars−Maessen mechanism is unfavorable since high activation energy is needed for Hg 0 reacting with the lattice oxygen of ZnO. The adsorbed H atoms by HCl dissociation inhibit the formation of HgCl 2 , and Cl 2 is the primary species being responsible for the Hg 0 oxidation on the ZnO surface.