Removal of elemental mercury (Hg⁰) from simulated flue gas over MnO_x-TiO₂ sorbents

A series of MnO_x modified TiO₂ based sorbents were synthesized using wet impregnation method and its performance on elemental mercury (Hg⁰) removal was studied. The effects of loading amount, calcination temperature, reaction temperature, and flue gas compositions on mercury removal efficiency were investigated. The sorbents were characterized by TGA, N₂ adsorption-desorption, XRD, FT-IR, XPS and Hg-TPD. It was shown that the optimum MnO_x loading value was 12%, and the optimal calcination and reaction temperature were 450 and 300 ℃, respectively. The highest mercury removal efficiency of MnO_x-TiO₂ sorbent was 98.46%. O₂ and HCl in flue gas played a positive role in mercury removal. SO₂ had a strong inhibitory effect on mercury removal, which may be due to the competition adsorption between SO₂ and Hg⁰. At the same time, the manganese sulfate produced during the reaction covered the surface of the active site, resulting in the decrease in mercury removal efficiency. CO₂ and NO in flue gas also slightly inhibited mercury removal. Mn⁴⁺ participated in oxidizing Hg⁰ to Hg²⁺, accompanied with its reduction to Mn³⁺. The adsorption and oxidation process of Hg⁰ over MnO_x-TiO₂ basically conformed to the Mars-Maessen mechanism and Langmuir-Hinshelwood mechanism.