Study On Removal Of Elemental Mercury Over MoO₃-CeO₂/Activated Coke In The Presence Of SO₂

Coal combustion is the main energy source in China and this structure would difficult to change in the short term.However,NO_X,SO₂,Hg⁰ and other pollutants released by coal-fired flue gas are one of the main causes for air pollution,among which mercury has attracted much attention due to its extremely strong physiological toxicity and bioaccumulation.Meanwhile,the volatility,low solubility,high mobility and durability of Hg⁰ make it hard to be controlled by existing air pollution prevention and control devices.Therefore,it is particularly important to explore efficient method to remove Hg⁰ from flue gas.This research adopted the impregnation method to modify the cylindrical commercial activated coke particles（AC）,and a series of modified activated coke（MoCe/AC）adsorption-catalyst loadding MoO₃ and CeO₂ were synthesized.The physical and chemical properties of the samples were analyzed by ICP-AES,SEM,EDX,BET,XRD and H₂-TPR,and the effects of Mo/Ce samples mole ratio and recation temperature on Hg⁰ removal performance were discussed.Under the optimal reaction conditions,the effects of different flue gas components（O₂,NO,SO₂ and H₂O）on Hg⁰ removal efficiency were investigated,and the stability,adsorption and regeneration of the optimal sample were also observed.The mechanism of Hg⁰removal by optimal sample was preliminarily deduced based on the experimental results and XPS characterization analysis.In addition,considering the low HCl and high SO₂ flue gas characteristics of coal burning in China,the sulfur resistance performance and mechanism of optimal sample without HCl were studied in detail.The experiment results showed that the optimal sample MoCe0.5/AC obtained the highest Hg⁰ removal efficiency as 94.74%at 120°C,as well as the high stability,SO₂ and H₂O resistance and regeneration performance.O₂ and NO could promote the removal of Hg⁰,while H₂O would compete the adsorption active sites with Hg⁰.SO₂inhibited mercury removal under pure N₂,but promoted it when co-existed with O₂.The characterization results showed that MoCe0.5/AC possessed special surface morphology,large BET surface area,well-dispersed metal oxides and high reducibility.Moreover,there was synergistic effect between Mo⁶⁺and Ce³⁺.The results of Hg-TPD experiments indicated that the chemisorption of Hg⁰ was the major approach for Hg⁰removal from flue gas by MoCe 0.5/AC.In addition,the chemisorbed mercury could be validly differentiated into weakly-HgO,strongly-HgO,O_α-HgO and HgSO₄（when SO₂ was added）.MoCe0.5/AC achieved the higher Hg⁰ removal efficiency than AC,which might due to the loading of metal oxides over the AC,causing the increase of Hg0 oxidation efficiency and the formation of O_α-HgO combined with lattice oxygen during the mercury removal process.The sulfur resistance of MoCe0.5/AC was mainly embodied in the following two aspects:first,the preferential combination of MoO₃ and SO₂ could protect CeO₂ for Hg⁰ removal.Second,the existence of SO₂could increase the surface chemisorbed oxygen and generate sulfate,which would promote the formation of weakly-HgO and HgSO₄,thereby improving the efficiency of Hg⁰ removal.