Integrated removal of NO and mercury from coal combustion flue gas using manganese oxides supported on TiO₂

A catalyst composed of manganese oxides supported on titania (MnO_x/TiO₂) synthesized by a sol-gel method was selected to remove nitric oxide and mercury jointly at a relatively low temperature in simulated flue gas from coal-fired power plants. The physico-chemical characteristics of catalysts were investigated by X-ray fluorescence (XRF), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses, etc. The effects of Mn loading, reaction temperature and individual flue gas components on denitration and Hg⁰ removal were examined. The results indicated that the optimal Mn/Ti molar ratio was 0.8 and the best working temperature was 240°C for NO conversion. O₂ and a proper ratio of [NH₃]/[NO] are essential for the denitration reaction. Both NO conversion and Hg⁰ removal efficiency could reach more than 80% when NO and Hg⁰ were removed simultaneously using Mn0.8Ti at 240°C. Hg⁰ removal efficiency slightly declined as the Mn content increased in the catalysts. The reaction temperature had no significant effect on Hg⁰ removal efficiency. O₂ and HCl had a promotional effect on Hg⁰ removal. SO₂ and NH₃ were observed to weaken Hg⁰ removal because of competitive adsorption. NO first facilitated Hg⁰ removal and then had an inhibiting effect as NO concentration increased without O₂, and it exhibited weak inhibition of Hg⁰ removal efficiency in the presence of O₂. The oxidation of Hg⁰ on MnO_x/TiO₂ follows the Mars-Maessen and Langmuir-Hinshelwood mechanisms.