Study on removal of elemental mercury over MoO3-CeO2/cylindrical activated coke in the presence of SO2 by Hg-temperature-programmed desorption

Abstract

MoO3-CeO2/cylindrical activated coke samples (MoCeY/AC) synthesized by an impregnation method were employed to investigate elemental mercury (Hg0) removal at 60–210 °C from simulated flue gas without HCl. MoCe0.5/AC with an optimal Mo/Ce molar ratio of 0.5 exhibited an excellent Hg0 removal efficiency (94.74%) at 120 °C, as well as good stability and prominent resistance to SO2 and H2O. The physicochemical property of the samples and the Hg0 removal mechanism were discussed by ICP-AES, SEM, EDX, BET, XRD, H2-TPR, XPS and Hg-TPD. The results of characterizations showed that MoCe0.5/AC possessed the special petal-like outer microstructure, large BET surface area, well-dispersed metal oxides and high reducibility, which was conducive for Hg0 removal. Furthermore, the synergistic effect between Mo6+ and Ce3+ was favorable to the high Hg0 removal performance by providing high valence Ce. According to the Hg-TPD tests, the chemisorption of Hg0 was a major approach for Hg0 removal, while physisorption and catalytic oxidation were just accounted for a tiny fraction. Moreover, the chemisorbed mercury could be validly distinguished into weakly-HgO, strongly-HgO, Oα-HgO and HgSO4 (when SO2 was added). Compared with raw AC, MoCe0.5/AC could enhance the Hg0 oxidation performance and produce Oα-HgO during the Hg0 removal process. In addition, the possible reason for the high SO2 tolerance of MoCe0.5/AC was examined: (i) the preferential combination between sulfate and MoO3 could protect CeO2 for Hg0 removal; (ii) SO2 could contribute to the formations of weakly-HgO and HgSO4. Finally, the regenerability of MoCe0.5/AC was also discussed.