Catalytic Oxidation Of Hg~0 Over Montmorillonite K 10 Supported Manganese Catalyst

Mercury emission has become a major environmental issue that attracts considerable global attention owing to its extreme toxicity,persistence,volatility,and bioaccumulation.As one of the dominant anthropogenic sources of mercury emission,coal combustion brings a large amount of elemental mercury?Hg0?into atmosphere.However,Hg0 removal is particularly difficult and challenging due to its high vapor pressure and low water solubility.The wide application of activated carbon injection technology is limited for its high operation cost and narrow temperature window.Thus,it is of great significance to develop novel materials that are highly-efficient,low-cost and wide-temperature-window.In this study,natural montmorillonite K 10 and Mn were used as support and active component,respectively.On the one hand,Hg0 removal performance over Mn/MKIO was conducted and compared with those over Mn/TiO₂,Mn/Al2O3 and Mn/SiO₂.Various characterizations,including Brunauer-Emmett-Teller?BET?,X-ray diffraction?XRD?,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?,temperature-programmed reduction?TPR?and temperature-programmed desorption?TPD?,were conducted to analyze the interaction mechanism between active component and support.On the other hand,the effects of preparation methods,loading amounts,and reaction temperatures on Hg0 removal over Mn/MK10 were investigated.The Hg0 removal mechanism under various gas components was discussed on the basis of characterization results.The results were obtained as follows:?1?The Hg0 removal performances of various Mn-based catalysts were explored,and the physicochemical properties and support effects of various catalysts were elucidated.The order of Hg0 removal efficiencies is as follows:4%Mn/MK10>4%Mn/SiO₂>4%Mn/TiO₂>4%Mn/Al2O3.The species,morphology,and valence state of MnOx are different in various catalysts,which affects Hg0 removal performance.?2?The reaction paths of Hg0 under different conditions over various Mn-based catalysts were investigated,and the structure-activity relationship between MnOx and Hg0 adsorption-oxidation was studied.Different mechanisms for Hg0 removal are carried out in different temperature ranges.Besides,amorphous Mn02 is beneficial for Hg0 oxidation,while amorphous Mn2O3 is also good for Hg0 oxidation at high temperature window.Whereas,the chemical adsorption is mainly promoted by crystalline Mn02.?3?The preparation process conditions of MK10 were optimized,and the intrinsic reason for its high efficiency of Mn/MK10 were investigated.4%Mn/MK10 prepared by acid activation impregnation was the optimal catalyst with outstanding Hg0 removal efficiency over the temperature range of 100-400?.The interaction between Mn and MK10 can form amorphous Mn4+,which is the main factor for its high activity compared with other transition metal catalysts.?4?The influence of flue gas components on Hg0 removal over Mn/MK10 was studied.Hg0 can be oxidized into HgO in O₂ atmosphere.NO has a promotion effect due to the formation of NO₂ and Hg?NO3?2.The addition of HCl leads to excellent Hg0 removal performance as HCl enhances Hg0 conversion to HgCl2.SO₂ and H2O?g?inhibit Hg0 oxidation ascribing to the formation of MnSO4 and the competitive adsorption with Hg0,respectively.Moreover,Hg0 removal performance is maintained at 80%-99%?NO/SO₂=0.26-1.71?in simulated flue gas without HCl,which indicates that Mn/MK10 has a great potential for industrial application.The main innovation of this study is the development of a novel catalyst with high Hg0 oxidation efficiency and wide temperature window,which is suitable for both low-chlorine and chlorine-free flue gases.