Synthesis Of Perovskite-Type Composite Oxide Catalyst And Its Application In Environmental Catalysis

The removal of soot particles from diesel engines and the degradation of organic compounds in printing and dyeing wastewater have been two major problems in the field of environmental protection.For the removal of soot particles and degradation of dyeing organic compounds,catalytic combustion oxidation technology is considered the most practical and efficient energy-saving method.Perovskite-type composite oxide is characterized by high activity,unique structure,inclusiveness,synthesis convenience,low cost,and non-toxicity,thus it is recognized as a promising catalyst for the above-mentioned two catalytic oxidation technologies.In this paper,perovskite-type composite oxide catalysts used in the combustion of diesel soot particles and the degradation of organic compounds in printing and dyeing wastewater were studied as follows:1.Study on Catalytic Combustion of Diesel Soot by Perovskite-typeCatalystsThere are two problems in terms of catalytic combustion of diesel soot:on the one hand,most of the perovskite-type catalyst activity screening is carried out on simulated carbon black,while large differences can be found between mock carbon black and actual diesel soot as their composition,structure and morphology.As the oxidation performances of mock carbon black and actual diesel soot are different,and the activities of selected catalysts are quite different from the actual ones.On the other hand,the actual diesel exhaust gas conditions are more complex,and the catalyst is usually supported on the diesel particulate filter.After being loaded,the engine back pressure will increase,further reducing the catalytic efficiency.At last,most experiments were carried out on the close contact mode between catalyst and soot in simulated air conditions.So the experimental results and the actual bench test results vary widely,which explains why diesel soot catalyst can not be utilized for industrial purpose.Therefore,this paper intends to study the oxidation performance of soot particles in the first place.Secondly,the activity and stability of the perovskite catalyst are improved by doping and modification.Finally,the catalyst activity is verified in the real diesel engine bench test.The relationship between the oxidation properties of soot particles and their chemical composition,particle size and phase structure was investigated by XRD,FT-IR,Raman Spectroscopy,SEM-EDS,BET,TEM and TG.The results showed that the actual diesel soot has a certain degree of graphitization,so it is more stable and hard to be oxidated than a mock carbon black.The temperature required for soot combustion totally is 660oC.LaCoO₃ and LaNi O₃ catalysts with high oxidation properties for soot were studied.The effects of catalyst preparation method（sol-gel method and colloidal crystal template method）on the surface structure,composition and soot catalytic activity of the catalyst were investigated.The results show that the preparation method of the catalyst will greatly affect the activity of the catalyst.Compared with LaCoO₃ synthesized by sol-gel method,the LaCoO₃synthesized by PMMA colloidal crystal template method is more homogeneous,and it has higher specific surface area,neat distribution of pores and exhibits higher soot oxidation activity.At the same time,the soot combustion performance of LaCoO₃ and LaNiO₃ catalysts were analyzed and studied by XRD,SEM,H₂-TPR and O₂-TPD.The mechanism of soot reaction was discussed in this paper.A novel reaction mechanism of diesel soot oxidation is proposed under the exhaust gas condition in diesel engine.It is removed by the"double oxidation"pathway under the combined action of NO and the surface active oxygen of the catalyst.The three-dimensionally ordered macroporous（3DOM）catalyst La_1-xSr_xCo_1-yNi_yO_3-δwith cubic crystal perovskite structure was synthesized by the colloidal crystal template method.Sr³⁺,Ni²⁺double substitution improves the redox performance of the catalyst.When the substitution amount of Sr³⁺and Ni²⁺is 0.1,the activity of the catalyst is the highest,and the peak temperature T_m is 361oC.A series of La_1-xSr_xTiO₃（x=0-0.6）perovskite catalysts were synthesized by citric acid complexation.With the increase of Sr substitution amount,the soot oxidation performance of the catalyst was improved obviously.When the amount of Sr-substitution is 0.3,the catalyst activity is the best and the T_m value is 422°C.Further increase the amount of Sr-substitution,the catalytic activity will be reduced.It may be related to the formation of TiO₂ phase which can destruct the complete perovskite-type crystal phase.The reaction between solid catalyst and the soot belongs to the gas-solid-solid called three-phase reaction.Apart from the influence of specific surface area,the soot oxidation performance is also affected by the oxygen content(O₂^-,O^-,O^2-)of the catalyst surface,the redox activity and the stability of the catalyst.In addition,the perovskite catalyst La_0.9Sr_0.1Co_0.9Ni_0.1O_3-δwith the best catalytic effect was coated on the engine post-processor,and the exhaust emission and conversion efficiency under the actual engine exhaust conditions were investigated.When the catalyst loading amount was 15 g cm^-3 and 30 g cm^-3,the soot conversion of the engine was 69%and 92%,respectively.When the catalyst amount coated on support was doubled,soot emissions increased by 17.3%.2.Study on Photocatalytic Degradation of Printing and Dyeing Wastewater by Perovskite-type catalystsThere are two main obstacles in the application of perovskite-type catalyst used to degrade organic compounds in printing and dyeing wastewater.Firstly,the perovskite-type catalyst has poor visible light response;Secondly,it is difficult and costly to recycle a powdered catalyst.Giving the two above mentioned problems,perovskite SrTiO₃ catalyst and K-doped Sr_1-xKxTiO₃catalyst were synthesized by sol-gel method in this paper.Furthermore,the above catalysts were hybridized with the polymer support“dopamine coated polyHIPEs”to form a novel composite material.Their photocatalytic performances were studied and the main conclusions are as follows:The perovskite-type SrTiO₃ catalyst synthesized by sol-gel method is compounded with the polymer support to form SrTiO₃@PC-polyHIPEs by impregnation method.The material had excellent UV-photocatalytic activity over the typical organic compound of methylene blue（MB）in dyeing wastewater.To our surprise,the novel composite could be excited by visible light.This is mainly due to the fact that the incorporation of inorganic support PC-polyHIPEs allows the absorption spectra of the composites to extend to the visible region.K-doping can improve the UV and visible photocatalytic properties of the composite Sr_1-xK_xTiO₃@PC-polyHIPEs.When x=0.3,the photocatalytic activity of the catalyst is the best for MB.In addition,the experimental conditions such as salinity,temperature and catalyst concentration will affect the catalytic activity of the material.The higher the salinity,the lower the activity;the higher the temperature,the lower the activity;the best catalyst concentration is 1.6 g_cata L^-1.The composite exhibits a stable morphology and a degradation rate of up to 85%after six photocatalytic reactions.Moreover,the synthetic material is a monolithic foamed material,which is easy to be recycled after the photocatalytic reaction,and greatly facilitates the industrial use of the material.