Preparation And Catalytic Performance Of Metal Oxide-based Hollow Structure Nanomaterials

Catalytic oxidation of CO to CO₂ has been one of the hottest topics over the past several decades because of its important applications in many fields including automobile exhausts emission control,fuel cell technology,as well as a prototypical reaction for het-erogeneous processes.Commonly used commercial catalysts are supported catalysts based on noble metal as the active component.The noble metal particles are easy to ag-glomerate in the process of heating and catalysis,so the specific surface area,pore struc-ture and thermal stability of the supports should be optimized.Among various well-de-fined structures,hollow nanostructures have attracted a great deal of attention due to their low density,high permeability,high porosity and high specific surface area.In this doc-toral dissertation,we prepare several hollow nanomaterials by hard template method,and improve the catalytic activity of the materials as far as possible on the basis of stability.Flower-like?-MnO₂ shell was coated on the surface of carbon spheres?CSs?,through in situ redox reaction between KMnO₄ and reductive carbon spheres.Au nano-particles with good dispersion of 5¹0 nm were loaded on the MnO₂ shell employing HAuCl₄ as the Au precursor.The as-prepared Au/MnO₂ hollow nanospheres could achieve complete catalytic oxidation of CO at 107^oC,and exhibited good stability.In addition,double-shell Au/MnO₂ hollow nanospheres were prepared on the condition of KMnO₄ and HAuCl₄ reacting with carbon spheres at the same time.In order to thoroughly solve the problem of agglomeration of Au nanoparticles,rat-tle-type Au@MnO₂ nanospheres were prepared by employing Au-cored CSs as templates.MnO₂ shell could protect interior Au nanoparticle from agglomeration.It was found that the thicker the shell,the lower the catalytic activity.It was also found that after calcination at 500^oC for 3 h,the?-MnO₂ shell would turn into nanowires with a relatively low cata-lytic activity.To solve the problem of thermal stability of hollow nanospheres,the CeO₂ supports were prepared.The hydrophilic groups on the surface of carbon spheres would adsorb Ce³⁺in solution,and the CeO₂ shell formed self-assembly layer-by-layer on the surface of carbon spheres.Au/CeO₂ hollow nanospheres were prepared by loading Au nanopar-ticles on the CeO₂ shell.The catalytic activity of Au/CeO₂ catalysts exhibited remarkable catalytic activity excellent stability.When the mass percentages of Au were 1.8%and4.2%,the complete catalytic oxidation temperature of CO was 98^oC and 81^oC,respec-tively.Finally,Ce_1-xFe_xO₂ hollow nanospheres were prepared between the reaction of CS@CeO₂ and K₂FeO₄.The molar ratios of Ce/Fe could be tuned.The complete conver-sion of CO on Ce_0.95Fe_0.05O₂ could be achieved at 297^oC.Besides,Ce_0.95Fe_0.05O₂ exhibited excellent thermal stability,which could maintain catalytic activity at 290^oC up to 40 h without any degradation.