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

This study demonstrates the high photo-oxidation efficiencies of elemental mercury (Hg-0) at high temperatures (120, 140, 160 degrees 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 Hg-0. The experimental results indicate that the highest Hg-0 photo-oxidation efficiency is achieved by TiO2 doped with 1-3% WO3, which result in a 4-fold increase in the Hg-0 photo-oxidation efficiency, as compared with TiO2. Simulated by the Langmuir-Hinshelwood model and thermodynamics analysis for Hg-0 photo-oxidation, the equilibrium constant (K-Hg0) and the change of Gibbs free energy (AG) are determined for the various photocatalysts. The enhancement of the Hg-0 photo-oxidation efficiency is mainly attributed to the increase of K-Hg0 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 Hg-0, but that it is enhanced by HCl. (C) 2016 Elsevier B.V. All rights reserved.