Structure-Property Relationship Studies Of Core@Shell Nano Materials And Their Applications In Heterogenous Catalysis

As the development of nanotechnology and structure-function theory,core@shell nanomaterials have become the research hotspot.The core@shell nanomaterial is a type of ordered structure composed by a core and a shell which are connected by physical or chemical force in nanoscale.The inner core usually do not contact with the external environment directly.However,it can change the physicochemical properties of the shell,such as transformation of the active sites,electromagnetic susceptibility,high specific surface area,high biocompatibility,etc.Benefiting from the properties,core@shell nanomaterials have been applied in chemistry,magnetics,electricity,optics,biomedicine,etc.Contrasted with monometallic and alloyed materials,core@shell structures can be controlled more easily to satisfy some special requests,such as controlling the active sites by adjusting the structure of the core@shell materials.However,due to lacking the study of the structure-function relationship,the understanding of the core and shell interaction and the theory about how to design core@shell catalysts are still big challenges for researchers.The dissertation aims to explore the relationship of the core@shell structure and the catalytic performance.Starting from bicomponent core@shell metallic nanomaterials,we introduce oxide and metal-organic frameworks to the system step by step,aiming to the utilization of carbon monoxide and carbon dioxide.The main work are as follows:(1)The fabrication of monometallic Pd nanoparticles was carried out at first.After that,the bicomponent core@shell metallic materials with different core morphology were synthesized successfully.Then,three-component core@shell metallic nanomaterials were developed and PdPt@Au core@shell material was found to be the best catalyst in carbon monoxide electrocatalytic oxidation.Based on these findings,the component ratio of the alloyed core was adjusted,which is important for the controlling of the active sites and the adsorption behavior of these special core@shell metallic nanocatalysts.(2)Metal/oxide system is the most widely used catalysts in heterogeneous catalysis.In this part,zinc oxide was introduced into the core@shell nanomaterials based on the former work,and the obtained ZnO supported metal catalysts(core@shell Ag@Pd/ZnO,alloyed AgPd/ZnO and simple Pd/ZnO)were utilized in carbon dioxide hydrogenation to methanol.It was found that the CO2 conversion and methanol selectivity of Ag@Pd/ZnO core@shell structure is the best,which can be due to the structure difference and the synergistic effect of the core and shell metals.(3)After the core@shell fabrication of the metal part,we tried to make the oxide part into core@shell structure in metal/oxide system.In this part,metal-organic frameworks were grown on the ZnO surface and the obtained materials were utilized as catalysts for carbon dioxide hydrogenation to methanol.In the typical Pd/ZnO catalysts,zeolitic imidazolate frameworks(ZIFs)were prepared on the surface of ZnO to fabricate ZnO@ZIF-8.The results indicated that the thickness of the ZIF-8 shell in Pd/ZnO@ZIF-8 affects strongly on the catalytic activity of the final product.