The performance and mechanism of Ag-doped CeO2/TiO2 catalysts in the catalytic oxidation of gaseous elemental mercury

Abstract

To improve the ability of CeO₂/TiO₂ catalysts to catalyze the oxidation of gaseous elemental mercury, silver was introduced. Doping with Ag can significantly enhance the Hg⁰ oxidation ability of CeO₂/TiO₂. In addition, the temperature window was widened (from 150 to 450 °C). The catalysts were characterized by TEM, XRD, XPS and H₂-TPR. The results indicated that silver nanoparticles can be loaded on the TiO₂ support. The catalysts had better crystallization and higher redox ability after addition of silver. Silver existed mostly in its metallic state, which can keep Ce in a higher Ce(IV) state. HCl was oxidized into active Cl by CeO₂ and then was adsorbed on the silver nanoparticles. In addition to the HCl and Hg⁰ breakthrough experiments, a Hg⁰ desorption experiment and a Cl₂ yield experiment were conducted to study the catalytic mechanisms of elemental mercury oxidation over various temperature ranges; these experiments indicated that the reaction followed the Langmuir–Hinshelwood mechanism at low temperature, and the Eley–Rideal mechanism and homogeneous gas-phase reaction at high temperature. Furthermore, a mercury valence state change experiment was performed, which indicated that HCl was the major catalytic oxidization component.