(314d) Mercury Oxidation Over Metal Bromide Catalysts for Simultaneous NOx Reduction and Mercury Oxidation

This study aims to develop Hg(0) oxidation catalysts that work in a temperature window (typically 350-400 °C) of the Selective Catalytic Reduction (SCR) unit at a typical coal-fired power plants.  Various metal bromides impregnated on TiO₂ and γ-Al₂O₃ were tested in a fixed bed reactor at 350 °C with a simulated flue gas containing 40 ppbv Hg(0), 10 ppm HCl, 2,000 ppm SO₂, 6% O₂, 12% CO₂, 10ppm NH₃ and 400 ppm NO.  Metal bromide/TiO₂ catalysts (both fresh and spent) were characterized by SEM-EDX, XAFS, Raman-IR, and XPS.  Hg(0) oxidation over metal bromideswas found to follow a Mars-Maessen mechanism by consuming lattice bromide which can then be regenerated with the help of HBr and O₂ gases via the Deacon reaction.  Metal bromides showed a good tolerance to NH₃ gas for Hg(0) oxidation.  Over 95% Hg(0) oxidation was achieved under simulated flue gas conditions, and 10 ppm NH₃ did not show any inhibition effect.  In addition, high SO₂ concentration (up to 2,000 ppm) did not show any negative effect on Hg(0) oxidation due to increased acidity on catalyst surface from metal bromides.  Metal bromide catalysts can be installed at the tail section of the SCR unit where a NH₃ gas concentration is low.  Oxidized mercury in the form of HgBr₂ is soluble in water and can be captured in a wet FGD process.