Development of Silica/Vanadia/Titania Catalysts for Removal of Elemental Mercury from Coal-Combustion Flue Gas

SiO2/V2O5/TiO2 catalysts were synthesized for removing elemental mercury (Hg0) from simulated coal-combustion flue gas. Experiments were carried out in fixed-bed reactors using both pellet and powder catalysts. In contrast to the SiO2−TiO2 composites developed in previous studies, the V2O5 based catalysts do not need ultraviolet light activation and have higher Hg0 oxidation efficiencies. For Hg0 removal by SiO2−V2O5 catalysts, the optimal V2O5 loading was found between 5 and 8%, which may correspond to a maximum coverage of polymeric vanadates on the catalyst surface. Hg0 oxidation follows an Eley−Rideal mechanism where HCl, NO, and NO2 are first adsorbed on the V2O5 active sites and then react with gas-phase Hg0. HCl, NO, and NO2 promote Hg oxidation, while SO2 has an insignificant effect and water vapor inhibits Hg0 oxidation. The SiO2−TiO2−V2O5 catalysts exhibit greater Hg0 oxidation efficiencies than SiO2−V2O5, may be because the V−O−Ti bonds are more active than the V−O−Si bonds. This superior oxidation capability is advantageous to power plants equipped with wet-scrubbers where oxidized Hg can be easily captured. The findings in this work revealed the importance of optimizing the composition and microstructures of SCR (selective catalytic reduction) catalysts for Hg0 oxidation in coal-combustion flue gas.