Complete catalytic reaction of mercury oxidation on CeO 2 /TiO 2 (001) surface: A DFT study.

CeO ₂ /TiO ₂ catalyst is a promising material for realizing the integration of denitrification and mercury removal to reduce mercury emissions. Oxidation mechanism of Hg ⁰ on CeO ₂ /TiO ₂ (001) surface in the presence of HCl and O ₂ was studied by density functional theory (DFT). The results indicated that Hg ⁰ was physically adsorbed on CeO ₂ /TiO ₂ (001) surface. As an important intermediate, HgCl was adsorbed on the surface of CeO ₂ /TiO ₂ (001) utilizing enhanced chemisorption, while the adsorption energy of HgCl ₂ was only -57.05 kJ/mol. In the absence of HCl, mercury oxidation followed the Mars-Maessen mechanism with a relatively high energy barrier, and the product (HgO) was difficult to desorb, which hindered the reaction process. When HCl existed, reactive chlorine (Cl*) would be produced by the dissociation of HCl, and the mercury oxidation would follow the Langmuir-Hinshelwood mechanism. The co-existence of HCl and O ₂ had no significant effect on the adsorption of Hg ⁰ , but reduced the reaction energy barrier and the final product (HgCl ₂ ) was more easily desorbed from the catalyst surface. In addition, two complete cyclic reaction pathways for catalytic oxidation of Hg ⁰ on CeO ₂ /TiO ₂ (001) surface were constructed to clarify the detailed reaction process.
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