Elemental Mercury Removal over CeO₂/TiO₂ Catalyst Prepared by Sol–Gel Method

Elemental mercury (Hg⁰) emitted from a coal-fired boiler is a serious menace and challenge to humans. Using high-efficiency CeO₂/TiO₂ catalysts to enhance the conversion from elemental mercury to oxidized mercury is a promising approach to reducing Hg⁰ emission. However, most of the CeO₂/TiO₂ catalysts were prepared by impregnation method or coprecipitation method while little attention has been paid to sol–gel method, which has many advantages in material production. In this study, a series of catalysts were synthesized through the sol–gel method to remove the gaseous Hg⁰ from simulated flue gas. The effect of vanadium (V) on Hg⁰ removal efficiency and the simultaneous removal of Hg⁰ and NO were also investigated. The results showed the optimal temperature for Hg⁰ removal over the CeO₂/TiO₂ catalysts was 350 °C. The oxidation of Hg⁰ could be promoted by O₂, HCl, and NO, but inhibited by NH₃ and SO₂. The addition of vanadium could enhance the Hg⁰ removal performance and the resistance to NH₃ and SO₂. A synergetic effect was found during the simultaneous removal of Hg⁰ and NO. The high redox reaction reactivity of Ce⁴⁺/Ce³⁺ and V⁵⁺/V⁴⁺ should take the credit for the oxidation of Hg⁰ and the removal of NO. Based upon the performance tests and the characterization experiments of the samples, the detailed mechanisms of the Hg⁰ and NO removal over the catalysts were proposed.