Preparation And Performance Study Of LDHs Derived Co-Fe Mixed Oxides For Catalytic Oxidation Of Toluene

As one of the main pollutants in the atmosphere,volatile organic compounds（VOCs）can cause serious harm to both human health and the environment.The regenerative catalytic combustion（RCO）process based on catalytic oxidation method is an effective approach in practical applications for the removal of low concentration and low value VOCs.Toluene is one kind of the most representative VOCs,Studying catalysts that can completely remove toluene at lower temperatures can guide the design optimization of RCO catalysts and solve the problem of expensive precious metal-based catalysts.Researches on catalysts which can completely removal of toluene at lower temperature can guide the design of RCO catalyst,and solve the expensive problem of precious metal-based catalysts.In this paper,a new efficient and stable RCO catalyst was prepared for industrial catalytic removal of toluene by optimizing layered double hydrotalcites（LDHs）-drived cobalt-iron mixed metal oxides.Besides,through the optimization of the preparation conditions,a monolithic catalyst based on iron mesh were synthesized to further improve its water resistance and high temperature resistance.Firstly,the coprecipitation method was used to prepare binary iron-based LDHs,the divalent metal elements and proportions in the LDHs was optimized.After calcination at 400 ^oC for 5 h,the catalysts with different chemical compositions were obtained.The optimized Co₃Fe-LDO catalyst showed the best catalytic activity and can achieve a toluene conversion of 90%at 286 ^oC(T₉₀).After 120 hours of testing,the catalytic activity did not decrease significantly.In addition,the toluene conversion was still as high as 91%after introducing 5 vol%water vapor at 290 ^oC.The results show that the optimized cobalt-iron mixed metal oxide presents excellent catalytic activity,water resistance and durability.Mn O₂/Co Fe-LDO composite catalyst with rich surface oxygen defects was prepared by the in-situ redox reaction between KMn O₄ solution and Co₃Fe-LDH.The T₅₀ and T₉₀ values of the preferred0.1Mn/Co₃Fe-LDO were 218 and 242 ^oC,respectively.After calcination at 500 ^oC for 5 h,the catalyst activity did not decrease significantly,90%toluene conversion could be achieved at around 250 ^oC.The mechanism study on toluene catalytic oxidation by powder catalyst showed that the large specific surface area,oxidation-reduction ability at lower temperature and abundant oxygen defects on surface are the main reasons for the high catalytic activity of cobalt-iron mixed metal oxides in the catalytic oxidation of toluene.Based on the powder catalyst,an iron-based monolithic cobalt-iron metal oxide catalyst was prepared in this paper.Compared with the traditional cordierite-based monolithic catalyst,the monolithic catalyst based on wire mesh presents higher catalytic activity,resistance and stability.The optimized 30-Co Fe-LDO/IM catalyst can achieve 50%and 90%toluene conversion at 316 _oC and 350 _oC,which is about 30^oC lower than cordierite-based catalysts.In addition,after introducing 3,5 and 10 vol%water vapor,the removal rate of toluene decreased to 84%,73%and 61%respectively at 350 ^oC,which was significantly better than Co Fe-LDO/Cordierite catalysts,which was 75%,56%and 45%.In addition,computational fluid dynamics（CFD）was used to analyse the internal heat distribution of the monolithic catalyst.The results show that due to the higher heat transfer efficiency of 30-Co Fe-LDO/IM catalyst,the internal temperature distribution was more uniform,which can avoid the common heat accumulation phenomenon in the process of using the traditional cordierite-based catalyst.The temperature difference between the front and back parts of 30-Co Fe-LDO/IM catalyst was only 2 ^oC,while the temperature difference of Co Fe-LDO/Cordierite of the same specification was as high as 20 ^oC.This may be the reason for the better stability and high temperature resistance of iron mesh-based catalyst.