Synthesis Of Hollow Structured Noble Metal-ceria Composites And Their Performance Study

CeO₂,one of most attractive rare earth oxides,displays outstanding properties such as excellent catalytic activity,remarkable chemical/thermal stability and the strong ability for storage/release of oxygen vacancies.It is widely used as the support for noble metal nanoparticles to improve catalytic activities in various reactions.Noble metal-CeO₂ composites have been widely employed in CO oxidation,water gas shift reaction,NOx reduction and solid oxide fuel cell in the past several decades,suggesting their important contributions in environmental remediation and green energy.There is a complex synergistic effect between CeO₂ and noble metals,and the structure type of the noble metal-cerium oxide composite is closely related to this effect.Therefore,the design of different structures of the noble metal-CeO₂ can control the catalytic activity of the catalyst.This paper focuses on controlled synthesis of noble metal-CeO₂ hollow composites with different structural types through interface reaction.In addition,controlled synthesis,structural characterization,formation mechanism,and properties are also investigated.The detailed information of the dissertation is listed as follows.1.Interfacial reaction-directed synthesis of embedded CeO₂-Pt nanotubes with high catalytic activity and thermal stabilityA catalyst based on CeO₂ nanotube-embedded ultra-small Pt nanoparticles was synthesized by means of an interfacial reaction in the absence of any surfactant and without involving any separate surface modification process.When Ce?OH?CO3 nanorods and H2PtCl6 are introduced into a NaOH aqueous solution in sequence,a solid-liquid interfacial reaction between Ce?OH?CO3 and NaOH occurs.The formed Ce?OH?3 then deposits on the external surface of Ce?OH?CO3 nanorods.During the interfacial reaction,the negatively charged Pt species is expected to be electrostatically attracted to gradually formed Ce?OH?3 due to its positive charge,resulting in a uniform mixture of Pt species and Ce?OH?3.After removing residual Ce?OH?CO3 and hydrogen reduction,CeO₂ nanotube-embedded Pt nanoparticle hollow composites were achieved.Due to the ultra-small size of catalytically active Pt nanoparticles and the close contact between Pt and CeO₂,the catalyst exhibits high catalytic activity toward CO oxidation and excellent thermal stability even at temperatures as high as 700?,suggesting that they also hold promise for higher temperature catalytic reactions.2.Dual template engaged synthesis of asymmetric hollow CeO₂-Au nanostructure by interfacial reationHollow materials with complex structure are of interest due to their promising properties arising from unique structural features.So far,this kind of architecture has mostly been achieved by means of either hard-template or sacrificial-template method,and the obtained hollow structures are generally symmetrical structures such as hollow “ball-in-ball” or “tube-in-tube”,which restricts the possible constructs of hollow materials with complex structure to certain extent.Herein,by combining of SiO₂ and Ce?OH?CO3 templates,hollow ball-in-tube structured CeO₂ is synthesized through a dual template engaged solid-liquid interfacial reaction,where the SiO₂ sphere?hard template?-embedded Ce?OH?CO3 nanorod?sacrificial template?composite is treated with NaOH solution,followed by an acid wash.The asymmetric hollow structured CeO₂ is shown to be an effective support for Au nanoparticles toward CO oxidation as compared to simple hollow CeO₂ nanotubes,leading to significantly enhanced catalytic activity.3.Synthesis of Au@CeO₂-MnO₂ nanotubes by interfacial redox methodThe sandwich core-shell hollow structure has attracted much attention due to its high catalytic activity and stability.In this context,Au@CeO₂-MnO₂ nanotubes with core-shell structure were prepared without any surfactant.Firstly,the solid-liquid interface reaction occurs between Ce?OH?CO3 and NaOH solution to produce a surface layer of CeO₂ on Ce?OH?CO3 surface,and then then the loading of Au particles was carried out.Then,through the interfacial redox reaction with the KMnO4 solution,the coating of the shell is carried out.KMnO4 reacts with the slowly released Ce3+ from Ce?OH?CO3 to form CeO₂-MnO₂ composite.Finally,the residual Ce?OH?CO3 template was removed by acid washing to obtain Au@CeO₂-MnO₂ nanotubes.Due to the rich interface between the binary oxides and the Au particles in the interlayer,Au@CeO₂-MnO₂ nanotubes exhibit high CO oxidation and 4-nitrophenol reduction catalytic activity.At the same time,the stability of Au nanoparticles was improved to some extent due to the existence of sandwich structure.