| Mercury, as a global pollutant, is volatile, heavy toxicity, persistence and bioaccumulation. It is harmful to environment and human health. Coal-fired flue gas is the biggest anthropogenic source of atmospheric mercury emission in the world. In addition, elemental mercury is the most important and most difficult forms to be controlled. Thus, to research a sorbent-catalyst, which is effective in removing Hg0 from coal-fired flue gas is of great significance. Mn-Ce mixed oxides supported on commercial columnar activated coke(Mn Ce/AC) were employed to remove elemental mercury(Hg0) from simulated coal-fired flue gas so as to develop a sorbent-catalyst which would effectively remove Hg0 from flue gas in the absence of HCl.A series of MnCe/AC samples were prepared by impregnation method. Effects of some factors, including Mn-Ce loading values, active component, reaction temperatures and flue gas components(O2, SO2, NO, H2O), on Hg0 removal efficiency were investigated. The samples were characterized by X-ray diffraction(XRD), Brunauer-Emmett-Teller(BET), X-ray photoelectron spectroscopy(XPS) and Temperature programmed desorption(TPD), and the results of the characterization were deal with by the corresponding software so as to analyze the physical and chemical properties of the samples. At last, the mechanism of Hg0 removal over MnCe/AC was indentified based on the results of experiment and the characterization of the samples.It was observed that Mn Ce/AC performed better than virgin activated coke, Mn/AC and Ce/AC, which indicated that Mn Ox and CeO2 have a synergy on Hg0 removal. Results indicated that the optimal Mn-Ce loading value and reaction temperature were 6% and 190°C, respectively. Considerable high Hg0 removal efficiency(>90%) can be obtained over MnCe6/AC under both N2/O2 atmosphere and simulated flue gas atmosphere at 190°C. Besides, it was observed that the flue gas components would affect the Hg0 removal efficiency to some degree, O2 and NO exerted a promotional effect on Hg0 removal, H2 O exhibited a suppressive effect, and SO2 hindered Hg0 removal seriously when in the absence of O2, however, the inhibition effect will be reduced largely after adding O2 into the flue gas. Furthermore, the XPS spectra of Hg 4f and Hg-TPD results showed that the captured mercury were existed as Hg0 and HgO on the Mn Ce6/AC, and HgO was the major species, which illustrated that adsorption and catalytic oxidation process were included for Hg0 removal over MnCe6/AC, and catalytic oxidation played the critical role. What's more, both lattice oxygen and chemisorbed oxygen or OH groups on MnCe6/AC contributed to Hg0 oxidation. Mn Ce6/AC, which exhibited excellent performance on Hg0 removal in the absence of HCl, appeared to be promising in industrial application, especially for low-rank coal fired flue gas. |
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