The enhancement of photo-oxidation efficiency of elemental mercury by immobilized WO3/TiO2 at high temperatures

• The photo-oxidation efficiency of Hg0 by TiO2, WO3/TiO2 prepared by sol-gel method and immobilization onto glass beads at high temperatures was investigated.
• The enhancement of photo-oxidation efficiency of Hg0 was achieved by WO3/TiO2 at high temperatures compared to TiO2(sol-gel) and TiO2(Degussa-P25) due to the doping WO3.
• The effects of a single gaseous component including HCl, SO2, NO, H2O, and CO2 was also investigated on the photo-oxidation efficiency of Hg0.

This study demonstrates the high photo-oxidation efficiencies of elemental mercury (Hg0) at high temperatures (120, 140, 160 °C) by WO3/TiO2. The photocatalysts TiO2(sol-gel) and 1–7% WO3/TiO2 prepared by sol-gel synthesis are immobilized on the surfaces of glass beads. The form of doped WO3 is characterized by SEM, HRTEM, XRD, Raman, PL, XPS, UV–vis spectrum and BET specific surface area analysis, respectively. The effects of gaseous pollutants in the flue gases emitted from coal-fired power plants, including HCl, NO, SO2, CO2 and H2O, are investigated as regards the photo-oxidation efficiency of Hg0. The experimental results indicate that the highest Hg0 photo-oxidation efficiency is achieved by TiO2 doped with 1–3% WO3, which result in a 4-fold increase in the Hg0 photo-oxidation efficiency, as compared with TiO2. Simulated by the Langmuir-Hinshelwood model and thermodynamics analysis for Hg0 photo-oxidation, the equilibrium constant (KHg0) and the change of Gibbs free energy (△G) are determined for the various photocatalysts. The enhancement of the Hg0 photo-oxidation efficiency is mainly attributed to the increase of KHg0 for WO3/TiO2 at high temperatures, as compared with TiO2(DegussaP25) and TiO2(sol-gel). This study further reveals that SO2, NO and H2O inhibit the photo-oxidation efficiency of Hg0, but that it is enhanced by HCl.

The schematic diagram of photo-oxidation of Hg0 by WO3/TiO2 under near-UV irradiation.Figure optionsDownload as PowerPoint slide