Heterogeneous Mercury Oxidation by HCl over CeO2 Catalyst: Density Functional Theory Study

CeO2-based catalysts have been regarded as potential materials for Hg removal due to high catalytic performance, nontoxicity, and low cost. Density functional theory calculations were performed to investigate the mercury oxidation mechanism by HCl over a CeO2 catalyst. The thermodynamic stability analysis suggests that the stoichiometric CeO2(111) is the most stable surface. The protonated CeO2 surfaces takes place at low oxygen partial pressures, and the chlorinated CeO2 surfaces can stably exist under low HCl concentrations. The adsorption energies and geometries show that Hg-0 is physically adsorbed on oxygen sites of the CeO2(111) surface and HCl is chemically adsorbed on the CeO2(111) surface. HCl can dissociate on the CeO2(111) surface with a low barrier. The Hg oxidation is most likely to proceed with the Eley-Rideal mechanism at the first step (Hg -> HgCl), followed by the Langmuir-Hinshelwood mechanism at the second step (HgCl -> HgCl2). In the whole Hg oxidation reaction, the formation of HgCl2 is the rate-determining step. The low energy barriers for the oxidation reaction of Hg on CeO2 make it an attractive alternative catalyst for Hg oxidation.