Preparation Of Porous/Hollow Metal Oxide Supported Ru Catalyst And Its Catalytic Performance Toward CO Oxidation

Porous/hollow structured materials are widely used as catalysts or metal particle supports due to their large specific surface area and good permeability,which facilitate the full exposure of active sites and diffusion of substrate molecules.It is well known that noble metals exhibit excellent catalytic properties in many catalytic reactions due to their unique d-electron structures.Although precious metals such as Au,Pt and Pd are considered to be the most effective catalysts for reactions such as oxidation and hydrogenation,their scarcity and high cost greatly limit their industrial applications.In contrast,Ru is relatively inexpensive.Therefore,the development of loaded Ru catalysts will reduce the cost of catalysts to some extent.In this paper,the construction of metal oxides with porous/hollow structures is firstly designed,followed by the support of Ru nanoparticles with different loading methods,and a series of characterization such as BET,XPS,H₂-TPR and CO-DRIFTS are used to further study the changes of Ru’s electronic structure and the influence of the interaction between the support and metal on the catalyst.The specific work is as follows:1.Metal organic frameworks（MOFs）-derived Cr₂O₃ supported Ru catalyst toward CO oxidationMetal-Organic Frameworks（MOFs）-derived oxides are considered as one of the excellent catalyst supports for noble metals due to their porous structure and high specific surface area features.In this work,the Cr₂O₃/Ru-1 catalyst is prepared by impregnation of Ru₃（CO）₁₂ solution into Cr-MOFs-derived Cr₂O₃.Thanks to the zero oxidation state of Ru in Ru₃（CO）₁₂,the H₂ reduction step is unnecessary.Interestingly,our results show that Cr₂O₃/Ru-1 present superior catalytic activity toward CO oxidation than that of Cr₂O₃/Ru-2catalyst,which is prepared by impregnation of Ru Cl₃ solution into Cr-MOFs-derived Cr₂O₃instead.To reveal the essential differences between these two kinds of Cr₂O₃/Ru catalysts,various kinds of characterization have been performed.Based on the studies by HRTEM and BET analysis results,the size of loaded Ru particles and the specific surface area of Cr₂O₃/Ru catalysts are almost the same.However,the XPS,H₂-TPR and in-situ CO-DRIFTS measurement results indicate that the interaction between MOFs-derived Cr₂O₃ and Ru are different for Cr₂O₃/Ru-1 and Cr₂O₃/Ru-2.This difference further causes the change of valence state of Ru,and even the adsorption and activation behavior of CO.Obviously,this work enriches the methods of preparation of supported Ru catalysts.Hopefully,this work is expected to present useful information for the understanding of catalytic mechanisms toward CO oxidation.2.Synthesis of defect-induced high-activity Ce O₂/Ru catalysts and their CO oxidation performance studiesCe³⁺and Ce⁴⁺in Ce O₂,undergo transformation under redox conditions thus making the Ce O₂ surface rich in oxygen defects.This defect facilitates the nucleation of precious metal particles as well as stabilizes the particles,and thus improves their stability.According to the literature,metal doping,chemical etching and reduction treatment are commonly used to enhance the defect concentration on the surface of Ce O₂ support.In the present work,Ce O₂nanorods and Ru Cl₃ were subjected to a simple hydrothermal treatment,accompanied by the continuous"dissolution"of Ce³⁺and the formation of Ce O₂,which led to the creation of pores within the nanorods.Moreover,the dispersion degree of Ru species was improved due to electrostatic adsorption.Compared with the conventional I-Ru/Ce O₂ prepared by impregnation,the catalyst prepared by this method contains more oxygen vacancies,larger specific surface area,higher Ru dispersion,and exhibits stronger CO adsorption and O₂dissociation activation,thus showing higher activity in the CO oxidation reaction.Finally,the relationship between catalyst structure and performance was further explained by a series of characterizations of the catalysts.3.Preparation of Ce O₂ nanotube loaded Ru catalysts and their CO oxidation performance studyThe hollow structure material has advantages such as high specific surface area,low density and good dispersion due to its special structure.The hollow structure Ce O₂ not only retains the advantages of hollow structure,but also effectively combines its own excellent redox properties and good stability.In this paper,NT-Ce O₂-Ru was synthesized by the solid-liquid interface reaction without using any surfactant.Specifically,Ce（OH）CO₃ was used as the precursor,and then the redox reaction occurred at the solid-liquid interface,where the Ce（OH）CO₃ precursor is reacted with Na OH aqueous solution.As the reaction proceeds,Ce（OH）₃ is formed on the surface of Ce（OH）CO₃.Ce（OH）₃,is unstable and it can be easily transformed into Ce O₂ by oxidation and dehyartion.During the interfacial reaction,Ru³⁺is well dispersed onto the Ce O₂ surface.When the residual Ce（OH）CO₃ is removed by acid washing,the NT-Ce O₂-Ru are developed.The hollow NT-Ce O₂-Ru showed better CO oxidation performance compared with the solid rod-shaped Ce O₂-loaded Ru samples obtained by thermal decomposition of Ce（OH）CO₃.