Toward predicting the mercury removal by chlorine on the ZnO surface

•HgCl2 is directly formed by the adsorbed Cl and Hg0 on the ZnO surface and not via HgCl intermediate.•The dissociated H atoms on the ZnO surface inhibit the formation of HgCl2.•Cl2 rather than HCl is responsible for the oxidation of Hg0 on the ZnO surface.•HgCl2 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 Cl2, HCl and Hg species on the ZnO(101¯0) surface, and the Hg0 oxidation mechanism by Cl2 (or HCl) on the ZnO surface. Cl2 and HCl are dissociatively adsorbed on the surface, and Cl atom bonds to two adjacent Zn atoms. Binding energy of Hg0 is showing a physisorption mechanism, while HgCl2 is strongly adsorbed on the surface in the molecularly mode, which indicates that the oxidation of Hg0 is necessary for its removal from flue gas. HgCl is not an indispensable intermediate during the Hg0 oxidation to form HgCl2. Three Hg0 oxidation mechanisms have been investigated, and the HgCl2 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 Hg0 reacting with the lattice oxygen of ZnO. The adsorbed H atoms by HCl dissociation inhibit the formation of HgCl2, and Cl2 is the primary species being responsible for the Hg0 oxidation on the ZnO surface.

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