Fe-modified MnOx/TiO2 as the SCR catalyst for simultaneous removal of NO and mercury from coal combustion flue gas

Abstract

Fe-modified MnOx/TiO2 (Fe-MnOx/TiO2) was synthesized by a sol-gel method and employed as the catalyst of selective catalytic reduction (SCR) for removing NO and mercury simultaneously from coal combustion flue gas. The experimental results demonstrated that Fe doping modified both NO and Hg0 removal performance of the catalyst. The optimal temperature for NO conversion was 200–250 °C, exhibiting good low-temperature activity, and lower temperature was also beneficial for Hg0 removal. The promotion of HCl on Hg0 removal efficiency was enhanced and the inhibitions of SO2 and NH3 were impaired after Fe doping on the catalyst. Effects of O2, NO and H2O on Hg0 removal efficiencies over MnOx/TiO2 and Fe-MnOx/TiO2 were all similar with each other. NO conversion and Hg0 removal efficiency could reach 76.8% and 65.6%, respectively, in simulated coal-fired flue gas at 250 °C and be maintained for a relatively long time. The modification mechanism of the Fe doping was investigated by characterization methods including BET, XRD, H2-TPR and XPS. The results showed that the introduction of Fe improved the BET surface area, the dispersity of the metal oxides, the redox behavior and surface concentrations of chemisorbed oxygen and Mn4+ of the catalysts, which was in favor of the catalytic activity. Meanwhile, Mn4+ could be protected by the existence of Fe to some extent when exposed to SO2 so that the sulfur resistance of the catalyst was strengthened as well.