Synthesis,Catalytic Properties And “structure-Activity” Relationship Of Ceria-Supported Bimetallic Small-Size Catalysts

Since the demand for energy and environment pollution,catalyst has attracted much interest due to its important role in these two areas.As a redox oxide support,ceria is crucial to industrial catalysis because of its rich oxygen vacancy.Ceria-supported metal or metal oxide catalysts are also widely used in various catalytic processes.Among them,bimetallic type exhibits different catalytic ability due to the synergistic effect between the two metals and interaction between the bimetallic component and the ceria support.However,the research on ceria-supported bimetallic catalyst was very limited.Specifically,how to identify the active site?How to explain the affects on interation between two metals or metal-support interaction?How to clarify the structure-activity relationship?In this dissertation,we prepared the ceria-supported bimetallic oxide catalyst with the deposition-precipitation method.By controlling the morphology,size,and distribution of small-size?nanoparticles,subnanometer clusters and single atoms?bimetallic oxide catalyst on the surface of ceria nanorods,as well as the investigations on the catalytic performance of carbon monoxide?CO?oxidation and Fischer-Tropsch Synthesis reactions,we have clarified the the structure-activity relationship between the structural evolutions and catalytic reactivity.Related research results are summarized as follows:1.CeO₂ supported cob alt-manganese oxide:In order to eliminate the harmful carbon monoxide and purify the hydrogen in the hydrogen fuel cells,ceria-supported cobalt oxide catalyst has been applied in the study of CO oxidation reaction.By using deposition-precipitation method,cobalt and manganese species were loaded onto the surface of ceria nanorods in different components.By using inductively coupled plasama spectroscopy?ICP?,X-ray diffraction?XRD?,transmission electron microscopy?TEM?,nitrogen adsorption-desorption measurements and other characterization techniques,we obtained the structural information on composition,crystal phase,morphology?size and shape?,surface areas,pore volumes and size?distributions of these ceria-supported bimetallic catalysts.On the basis of catalytic test results,we found that the CO oxidation reactivity of ceria-supported bimetallic cobalt-manganese oxide sample is higher than that of ceria-supported single cobalt or manganese oxide samples.The aberration-corrected,high-angle,annular dark-field scanning transmission electron microscopy?HAADF-STEM?images and X-ray absorption fine structure?XAFS?analysis on the fresh samples demonstrated the presence of a Co₃O₄ phase for cobalt species on the surface of ceria nanorods.The fitting results of the extended X-ray absorption fine structure?EXAFS?indicated that the introduction of a secondary metal?Mn?oxide significantly enhanced the two-dimensional growth of cobalt oxide nanostructures on the surface of CeO₂.Therefore,the promotion on CO oxidation activity for bimetallic cobalt-manganese oxide catalyst can be attributed to the higher crystallinity of Co₃O₄ phase.2.CeO₂ supported copper-silver oxide:In order to eliminate the harmful carbon monoxide and purify the hydrogen in the hydrogen fuel cells,ceria-supported copper catalyst has been applied in the research of CO oxidation reaction.By using deposition-precipitation method,copper and silver species were loaded onto the surface of ceria nanorods in different components.By using ICP,XRD,TEM and other characterization techniques,we obtained the structural information on composition,crystal phase and morphology of these ceria-supported bimetallic catalysts.The HAADF-STEM images analysis on the fresh samples demonstrated the high distribution of CuO_x species on the surface of ceria nanorods.The related temperature-programmed reduction by hydrogen?H₂-TPR?confirmed the strong interaction between the copper oxide species and the ceria nanorods.On the basis of catalytic test results,we found that the CO oxidation reactivity of ceria-supported bimetallic copper-silver oxide samples is nearly equal to that of ceria-supported single copper oxide sample.3.CeO₂ supported iron-ruthenium oxide:In order to alieviate the energy crisis and improve the production rate of Fischer-Tropsch synthesis,ceria-supported iron catalyst has been applied in the research of Fischer-Tropsch synthesis reaction.By using deposition-precipitation method,iron and ruthenium species were loaded onto the surface of ceria nanorods.According to the inductively coupled plasama spectroscopy,X-ray diffraction;transmission electron microscopy,nitrogen adsorption-desorption measurements and other characterization data,we obtained the structural information on composition,crystal phase,morphology?size and shape?,surface areas,pore volumes and size-distributions of these ceria-supported bimetallic catalysts.On the basis of catalytic test results,we found that the Fischer-Tropsch synthesis reactivity of ceria-supported bimetallic iron-ruthenium oxide sample was obviously different from that of single iron oxide sample.The aberration-corrected HAADF-STEM and XAFS analysis on both fresh and used catalysts demonstrated the structural evolution on iron species from sub-nanometer cluster to single atom.The corresponding fitting results of EXAFS indicated that the introduction of a secondary metal?Ru?oxide significantly weakened the interaction between iron species and ceria nanorods.The above experimental results have provided deep insight into the fabrication of ceria-supported bimetallic oxide catalyst,as well as the identification of active center,and thus given a significant guidance to the research of the structure-activity relationship.