Removal of gaseous elemental mercury over a CeO2–WO3/TiO2 nanocomposite in simulated coal-fired flue gas

This paper discussed a recent study of elemental mercury removal by gaseous hydrogen chloride over novel CeO2–WO3/TiO2 catalysts under bench scale conditions. The performances of mercury removal over the catalysts were tested in simulated flue gas with 80–100 μg m−3 Hg0, 8% O2, 10 ppm HCl, 8% H2O, 800 ppm SO2 and balanced with N2. Results indicated that about 95% of the Hg0 could be removed by hydrogen chloride over the CeO2–WO3/TiO2 catalysts in the presence of O2, and the HgO that formed was effectively converted to mercury chloride when hydrogen chloride was added to the system. The Hg0 removal efficiency was found to be slightly but significantly affected by H2O and SO2 addition. Water vapor slightly inhibited the Hg0 removal efficiency, due to the competitive adsorption. By contrast, SO2 promoted the oxidation reactions, resulting in higher Hg0 removal efficiencies. The Hg-TPD and SO2-TPD results indicated that less negative effect of Hg adsorption with/without water vapor and less adsorption mass of SO2 might be responsible for the tolerance of the catalysts to H2O and SO2. From the characterization results, the BET surface areas had no significant influence on the catalytic performance. The XRD pattern indicated that cubic CeO2 crystallite was the crystalline form on the surface. The XPS and H2-TPR results suggested that Ce4+ oxide was the main form of Ce on the catalysts surfaces, which was beneficial for the Hg0 removal reactions.