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

Abstract

A catalyst composed of manganese oxides supported on titania (MnOx/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 MnOx/TiO2 follows the Mars–Maessen and Langmuir–Hinshelwood mechanisms.