Catalytic oxidation and capture of elemental mercury from simulated flue gas using Mn-doped titanium dioxide

Titanium dioxide (TiO₂) and Mn-doped TiO₂ (Mn(x)-TiO₂) were synthesized in a sol-gel method and characterized by BET surface area analysis, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Gasphase elemental mercury (Hg⁰) oxidation and capture by the Mn-doped TiO₂ catalyst was studied in the simulated flue gas in a fixed-bed reactor. The investigation of the influence of Mn loading, flue gas components (SO₂, NO, O₂, and H₂O) showed that the Hg⁰ capture capability of Mn(x)-TiO₂ was much higher than that of pure TiO₂. The addition of Mn inhibits the grain growth of TiO₂ and improves the porous structure parameters of Mn(x)-TiO₂. Excellent Hg⁰ oxidation performance was observed with the catalyst with 10% of Mn loading ratio and 97% of Hg⁰ oxidation was achieved under the test condition (120 °C, N₂/6%O₂). The presence of O₂ and NO had positive effect on the Hg⁰ removal efficiency, while mercury capture capacity was reduced in the presence of SO₂ and H₂O. XPS spectra results reveal that the mercury is mainly present in its oxidized form (HgO) in the spent catalyst and Mn⁴⁺ doped on the surface of TiO₂ is partially converted into Mn³⁺ which indicates Mn and the lattice oxygen are involved in Hg⁰ oxidation reactions.