Design Of CeO₂ Based Catalyst And Study On Catalytic Oxidation Performance Of CO At Low Temperature

Since the industrial revolution,how to deal with CO efficiently and environmentally has always been a problem of environmental protection,research results in recent years show that the use of thermal catalytic oxidation technology to oxidize CO into CO2 under low temperature is currently the most effective way to solve the CO environmental pollution problem.As a rare earth oxide with strong oxygen storage capacity,abundant active sites and low price,CeO2 has been widely used in catalytic oxidation of CO and degradation of organic pollutants.However,single CeO2 has the disadvantage of low ROS migration efficiency,which makes higher temperatures are needed for CO catalytic oxidation.To solve this problem,researchers on the one hand improved the catalytic oxidation activity of CeO2 to CO by morphology regulation,on the other hand,further reduced the CO catalytic oxidation temperature by element doping.In this thesis,Cube-like,spherical and core-shell CeO2 catalysts were designed and synthesized under different experimental conditions.Through a series of characterization results,the internal structure characteristics and physical and chemical properties of CeO2 with different morphologies were analyzed.Combined with the CO catalytic oxidation experiment results,the influence of CeO2 catalysts with different morphologies on CO catalytic oxidation was systematically clarified.In addition,this paper also carried out In ion doping on the core-shell CeO2 to synthesize the core-shell In-CeO2 composite material.At the same time,the basic structure of this material was systematically explored and analyzed.The main research contents of this thesis are as follows:1.Cubic CeO2 was synthesized by different methods,and the effects of different hydrothermal reaction temperatures on the physical properties and internal structure of the products were studied by various characterization methods.The influence of cubic CeO2 synthesized at different hydrothermal reaction temperatures on the catalytic activity of CO oxidation was also analyzed.Combined with the results of CO catalytic oxidation experiments and characterization,it can be concluded that under the condition of low hydrothermal reaction temperature,the production of cubic CeO2 is adversely affected,and the crystallinity of CeO2 is poor and agglomeration often occurs.However,with the continuous increase of temperature,the crystallinity is improved with it,the dispersion is optimized,the purity is improved,and the shape of the cube is more regular However,it is speculated that the high temperature may cause the cube to grow rapidly,and a large number of active edges of CeO2 are buried,which is not conducive to the exposure of more active sites of CeO2.Therefore,in a certain temperature range(140-220℃),the increase of hydrothermal reaction temperature is conducive to the formation of cubic CeO2.Through the study of catalytic oxidation activity,it is found that the cubic CeO2 with high purity,large specific surface area and large mobility of lattice oxygen has the best catalytic activity for CO.2.The effects of different hydrothermal reaction time on the physical properties and internal structure of spherical CeO2 were studied.At the same time,the basic effect of different hydrothermal reaction time on the catalytic activity of CO oxidation was explored.Combined with the CO catalytic oxidation experiment and characterization results,it can be found that too short hydrothermal reaction time is not conducive to the formation of spherical CeO2,the crystallinity of CeO2 is poor,and the agglomeration phenomenon is more serious.With the extension of reaction time,the crystallinity becomes more ideal,the dispersion is improved,and the shape of the ball is more standardized.Therefore,in a certain time range(2.5h-8h),when the reaction time is prolonged,the crystallinity becomes more ideal In this case,the production of spherical CeO2 was promoted.Through the study of catalytic oxidation activity,it is found that spherical CeO2 with high purity,large specific surface area,high defect degree and large lattice oxygen mobility has the best catalytic activity for CO oxidation.3.CeO2 with core-shell structure was synthesized by different precursors.The results show that the average particle size and cell parameters of CeO2 with core-shell structure synthesized at different hydrothermal reaction temperatures are quite different.The precursor is CeCl3·7H2O.The morphology of CeO2 prepared by this method is irregular core-shell structure with poor dispersion,serious agglomeration and uneven particle size.The CeO2 prepared by Ce(NO3)36H2O precursor has a core-shell structure,no agglomeration,good dispersion and good homogeneity.4.The average particle size of the synthesized core-shell like In-CeO2 nanoparticles is larger than that of pure core-shell like CeO2,and there are many defects in the nanoparticles,which increase the gap between CeO2 crystal planes.Compared with pure core-shell CeO2,the CO catalytic oxidation performance of core-shell like In-CeO2 have greatly improved,compared with cube-like and spherical CeO2,the CO catalytic oxidation reaction temperature is significantly reduced to 150℃.Analyzed CO catalytic oxidation activity of the synthesized CeO2 material.The core-shell CeO2(T50=465℃)<spherical CeO2(T100=340℃)<core-shell CeO2(T100=274℃)<core-shell In-CeO2(T100=150℃).Compared with Cube-like CeO2,spherical CeO2 and pure core-shell CeO2,the CO catalytic oxidation performance of core-shell In-CeO2 is greatly improved.This is because the doping of In ions caused the lattice expansion of CeO2,which leads to structural defects,the oxygen vacancy of CeO2 increases.Therefore,the catalytic activity of the core-shell like In-CeO2 was improved.In this thesis,by controlling the reaction conditions of hydrothermal synthesis method,simple preparation of CeO2 with different morphologies was realized.By introducing a large number of oxygen vacancies through In doping,the CO catalytic oxidation activity of core-shell In-CeO2 was greatly improved,which provide a feasible theoretical basis and idea for CO low temperature catalytic oxidation of Ce based catalyst.