Removal Of Elemental Mercury By Co/Ce Modified Mesoporous Silica Based Catalysts

According to statistics of the energy demand of China in 2016,the energy requirement will incerease continuously.In Chinese energy structure,coal which contains Hg⁰ and used in thermal power generation occupies a considerable proportion.During the combustion process,Hg⁰ will volatilize first due to its strong volatility,and it is difficult to remove it by the existing technologies.Therefore,we need to develop new Hg⁰ control technologies.The current research shows that catalytic oxidation method has high removal efficiency of Hg⁰,and the oxidized Hg²⁺can be removed by existing devices.Meanwhile,the catalyst can be regenerated.Therefore,in recent years,many studies focused on catalytic oxidation to remove Hg⁰.However,most of the current carriers have irregular pores,so the resistance during the mass transfer of the catalytic reaction is large,which is not conducive to the catalyst reaction at high space velocity.In order to solve the problem of large carrier mass transfer resistance in the Hg⁰removal reaction,the MCM-41 carrier with one-dimensional ordered pore structure was selected to remove Hg⁰ by loading Co and Ce.Then the KIT-6 carrier with three-dimensionally ordered pores was loaded with the same content of Co and Ce,and the comparative study on the removal of Hg⁰ from the two carriers was performed.In order to further improve the dispersion of the active component on the surface of the support,natural mineral halloysite with both ends open was selected as the carrier.Catalysts preparated by hydrothermal synthesis to remove Hg⁰ are studied,and a similar method was used to synthesize M-MCM-41.The MCM-41 catalyst was used to measure the removal efficiency of Hg⁰.Firstly,the catalysts with different contents of Co and Ce supported on MCM-41 prepared by impregnation method were studied.The test results show that Co_0.15-Ce_0.15/MCM-41 has about 90%Hg⁰ removal efficiency at 250 ^oC.On top of that,catalysts with different Co and Ce loadings on MCM-41 were also prepared.As a result,it was found that when Co/Ce was 1:1,the Hg⁰ removal efficiency of the catalyst was optimal.The study of the adsorption and oxidation of the catalyst in the removal process of Hg⁰ shows that the adsorption process is the main one in the initial stage of Hg⁰ removal.In order to study the effect of different carriers on the activity of the catalysts,a Co_x-Ce_x/KIT-6 catalyst with the same loading as Co_x-Ce_x/MCM-41 was prepared and compared using the same method.The Hg⁰ removal results of the catalysts showed that Co_x-Ce_x/KIT-6catalyst exhibits more excellent Hg⁰ removal efficiency.Due to the complex cross-channel inside KIT-6 and larger pores than MCM-41,the active components can be dispersed in the pores to expose more active sites and improve the Hg⁰ removal efficiency of the catalyst.In order to further improve the dispersion of the active component,a direct hydrothermal synthesis method was used to prepare the Co/halloysite catalyst for the removal of Hg⁰.When the loading of Co is 5%and 10%,the catalyst can exhibit about 80%activity at 250 ^oC.At the same time,a series of metal-doped MCM-41 catalysts were prepared using a one-step hydrothermal synthesis method.However,the corresponding catalysts have a low activity,which may be due to the high coordination saturation of the metal ions entering the catalyst framework.Since Hg⁰ has poor adsorption,it is difficult to remove Hg⁰.By studying the effect of different flue gas on the removal efficiency of Hg⁰,it was found that O₂ and NO promote the removal of Hg⁰,while H₂O and SO₂ show the inhibitory effect on the removal of Hg⁰.