Preparation Of Manganese-based Catalysts And Study On Denitrification Performance Of NH₃-SCR

In this paper,using self-prepared halloysite/carbon composites?HAL/C?and natural clay mineral halloysite?HAL?as the NH₃-SCR catalyst carrier,and then adopted impregnation method and hydrothermal method to prepared two manganese-based catalysts,respectively.The effects of MnOx loading and preparation conditions on the morphology,structure and catalytic performance of the catalyst were investigated.The NH₃-SCR reaction mechanism of hydrothermal manganese-based halloysite catalyst was also preliminarily investigated.The main conclusions were as follows:?1?Halloysite/carbon composites?HAL/C?was prepared via the carbonization of chitosan as carbon source at high temperature.Then HAL/C was used as the NH₃-SCR catalyst carrier to prepare manganese-based catalyst by a conventional impregnation method.The effects of different clay/carbon composites?halloysite/carbon,sepiolite/carbon,montmorillonite/carbon and attapulgite/carbon?as catalyst carrier on the catalytic performance of catalyst were compared.The effects of mass ratio of chitosan to halloysite and the Mn loading on the catalytic performance aslo were studied.The results showed halloysite/carbon composite as carrier exhibited the best NH₃-SCR activity,and the introduction of carbon in the carrier could significantly improved the NH₃-SCR catalytic.When the mass ratio of chitosan to halloysite was 2,HAL/C had the largest specific surface area and the most developed pore structure.Then using that as the caarier and the content of Mn loading was 12 wt.%,the obtained catalyst(Mn₁₂-HAL/C-2)showed the best catalytic performance with a 95-100%NO conversion in the temperature of 150-300 ^oC,which was superior to the manganese loaded origin halloysite and pure carbon catalyst.In addition,the addition of an appropriate amount of carbon in the carrier increased the content of oxygen-containing functional groups and adsorbed oxygen in the catalyst,and also increased the number of acidic sites in the catalyst,thereby improving the catalytic performance of the catalyst.?2?One-step mild hydrothermal method was adopted to prepared manganese-based catalyst with using halloysite as the template and KMnO₄ as the high-valence precursor.The results showed that Mn6/HAl catalyst with 6 wt.%Mn loading and a condition of160 ^oC hydrothermal temperature for 48 h owned a wide active temperature window and the best NH₃-SCR performance.It achieved a NO conversion of 88%at 150 ^oC,and nearly 100%NO conversion in the temperature of 250-350 ^oC as well as 90%NO conversion at 400 ^oC,which is more high than the catalytic performance of origin halloysite and pure MnOx.Therefore,halloysite as the catalyst carrier could greatly enhance the catalytic activity of catalyst.In case of Mn6/HAL catalyst,MnOx was evenly distributed on the surface of halloysite in form of flakes,and the specific surface area as well as pore volume were better than that of original halloysite and pure MnOx.Besides,halloysite as a template improved the agglomeration of active component MnOx,and increased the aicid sited for catalyst and then to promoting the NH₃-SCR performance.?3?The NH₃-SCR reaction mechanism of manganese-based halloyiste catalyst was studied by NH₃-TPD,NO-TPD,NO+NH₃-TPD,H₂-TPR and TPSR,the results indicated that halloysite enhanced the adsorption capacity of catalyst for NH₃ and NO as well as provided more acid sites,which further suggested that superior catalytic performance was benefited from the combined action of halloysite and MnOx.In addtion,there were two acidic sites on the surface of the Mn-based halloysite catalyst:Lewis and Br?nsted,and Lewis acids was dominant.The adsorption of NO led to form two NOx species:monodentate nitrite and gaseous NO₂.In the process of NH₃-SCR reaction,monodentate nitrite participated in NH₃-SCR reaction,mainly following the L-H mechanism in the low temperature?<250 ^oC?,and the E-R mechanism was involved in the high temperature?>250 ^oC?,and the NO₂ on the catalyst surface participated in the fast SCR reaction...