Design And Catalytic Performance Of Ce-Mn Bimetallic Oxide With Interfacial Reaction

Transition metal oxides,which can be used as multiphase catalysts,have received much attention in the field of catalysis due to their high stability,easy availability and low cost.The catalytic performance of bimetallic oxides is significantly better than that of single-component metal oxides due to the synergistic effect between the components.It is well known that the catalytic performance of bimetallic oxides is closely related to their morphology,size and crystal structure.Therefore,by reasonably regulating the above conditions,we can expect to obtain bimetallic oxide materials with high catalytic activity.At present,researchers have developed various strategies for the preparation of bimetallic oxides,however,the materials obtained by current methods often suffer from uneven distribution of components and small specific surface area,leading to a reduction in catalytic activity.Therefore,in this thesis,we designed to prepare cerium-manganese bimetallic oxides by interfacial reactions using different templates.The experimental results show that the cerium-manganese bimetallic oxide catalysts with porous structure,close contact of components and exposure of more active sites not only facilitate the full contact between the reaction substrate and the active sites inside the catalyst in the catalytic reaction,but also give full play to the synergistic effect between the components.1.Synthesis of CeO₂-MnO₂ by interfacial reactions involving water-soluble templates for alcohol-amine coupled oxidationA porous CeO₂-MnO₂ catalyst was successfully prepared by using the interfacial redox reaction between Ce₂（SO₄）₃ precursor and aqueous KMnO₄ solution without surfactant and surface modification.Specifically,the strongly oxidizing MnO₄^-and Ce³⁺undergo redox reaction at the surface of Ce₂（SO₄）₃ precursor,and MnO₄^-is reduced to MnO₂;Ce³⁺is oxidized to Ce⁴⁺and then hydrolyzed to form CeO₂ thus,the MnO₂ nucleated on the surface of Ce₂（SO₄）₃precursor grows in close contact with CeO₂ More importantly,the residual Ce₂（SO₄）₃ template can be removed with water without the need for high-temperature calcination or acid/base dissolution.The catalytic results show that CeO₂-MnO₂ catalytic performance is superior to that of single-component and physically mixed samples in the alcohol-amine coupled oxidation to imine reaction.We have explored it in depth by a series of characterizations such as XPS,Raman and H₂-TPR.The preparation method is expected to be extended to the preparation of other bimetallic oxides.2.Preparation of CeO₂-MnO₂ core-shell structure catalysts by interfacial reaction involving MnCO₃ and their selective catalytic oxidation performance of 5-hydroxymethylfurfuralCore-shell structure materials can be used to optimize catalyst performance by regulating the core and shell components as well as the thickness of the shell layer.Currently,the design of bimetallic oxide core-shell structures with CeO₂ as the shell layer relies on the precipitation of CeO₂ on the surface of the inner core oxide by hydrolysis and other methods,which is simple but unevenly coated and prone to homogeneous nucleation of CeO₂.In this work,the cube-shaped MnCO₃ was selected as the sacrificial template and dispersed in cerous nitrate aqueous solution.OH^-produced by CO₃^2-hydrolysis in MnCO₃ reacted with Ce³⁺on the surface of the MnCO₃ template.After oxidation and dehydration,CeO₂ was finally formed,and the residual MnCO₃ was calcined to obtain MnO₂.Obviously,this work enriches the preparation methods of bimetallic oxide core-shell structures with CeO₂ as shell layer.The catalytic and characterization results show that the obtained MnO₂@CeO₂ core-shell structure catalysts exhibit good activity in the selective oxidation of 5-hydroxymethylfurfural.3.Synthesis of CeO₂-MnO₂ hollow sphere structure catalysts by interfacial reaction involving carbon spheresConsidering the lower density and larger specific surface area of hollow micro/nanostructures,as well as the synergistic effects exhibited by the above-mentioned cerium-manganese binary oxides in catalytic reactions,we envisioned the preparation of a hollow micro/nanostructure of CeO₂-MnO₂,which is expected to take full advantage of its geometric structure and components in catalytic reactions.In this work,we used carbon spheres as templates to fully impregnate aqueous solutions of a mixture of ceric ammonium nitrate and potassium permanganate.During the impregnation process,MnO₄^-was reduced to MnO₂ by interfacial reaction with C while Ce⁴⁺could be uniformly adsorbed on the material surface.After high temperature calcination,the template is removed and at the same time the CeO₂-MnO₂ with hollow structure is finally obtained.compared with the literature,this method has concise steps and uses Ce⁴⁺instead of Ce³⁺to avoid the strong oxidizing MnO₄^-to nucleate in the same phase with Ce³⁺in aqueous solution.The characterization and performance test results showed that the hollow structure of CeO₂-MnO₂ and the synergistic effect between the two resulted in good CO oxidation activity.