Preparation Of UiO-66-based Noble Metal/Acid Multifunctional Catalysts And Their Catalytic Performance

Metal-Organic Frameworks?MOFs?,formed by self-assembly of inorganic metal ions or clusters and organic ligands,are a relatively new type of porous solid materials.Compared with traditional porous materials,their high porosity,large specific surface area,tunable pore size and facile chemical post-modification,make them potential candidates in heterogeneous catalysis.However,the type and content of catalytic centers in bulk MOFs are limited,and they need to be further functionalized to improve their application range.Based on the properties and characteristics of UiO-66 with two different metal centers of zirconium?Zr?and/or hafnium?Hf?,in this master's thesis,UiO-66-based noble metal/acid multifunctional catalysts were prepared by different method via integration of noble metal nanoparticles and acid centers within the UiO-66 nanocrystals.The physicochemical properties of the prepared catalysts were systemically characterized by X-ray powder diffraction?XRD?,N2 adsorption,infrared spectroscopy?FT-IR?,X-ray photoelectron spectroscopy?XPS?and transmission electron microscopy?TEM?techniques.Subsequently,these catalysts were evaluated in the hydrogenation of2,3,5-trimethylphenylhydrazine?TMBQ?to 2,3,5-trimethylhydroquinone?TMHQ?,a vitamin-E intermediate,and the hydrogenation cyclization of methyl levulinate?ML?to?-valerolactone?GVL?,respectively.The main results are briefly summarized as follows:?1?The conversion of TMBQ to TMHQ is regarded as one of the most important reactions for the production of vitamin E.In this master's thesis,we reported on a Hf-based metal-organic framework?MOF?,UiO-66?Hf?,with supported palladium nanoparticles as a highly active,selective,and recyclable catalyst for the direct hydrogenation of TMBQ with H₂ under mild reaction conditions?45°C and 0.4 MPa H2 pressure?.The developed Pd/UiO-66?Hf?catalyst exhibited a marked increase in activity compared with its Pd/UiO-66?Zr?counterpart and conventional Pd/C catalysts.Its excellent catalytic performance is ascribed to the Br?nsted acid sites in the UiO-66?Hf?framework,which promote the adsorption and activation of TMBQ.?2?The synthesis of heterogeneous cooperative catalysts in which two or more catalytically active components are spatially separated within a single material has stimulated considerable research efforts.The multiple functionalities of catalysts can significantly improve the efficiency of existing organic chemical transformations.In this master's thesis,we introduced ruthenium?Ru?nanoparticles?NPs?on the surfaces of a metal-organic framework pre-encapsulated with polyoxometalate silicotungstic acid?HSiW?UiO-66?Zr?and prepared a2.0 wt%Ru/11.7 wt%HSiW@UiO-66?Zr?porous hybrid using the impregnation method.The close synergistic effect of metal Ru NPs,HSiW and UiO-66?Zr?endow 2.0 wt%Ru/11.7wt%HSiW@UiO-66?Zr?with increased activity and stability for complete ML conversion and exclusive GVL selectivity at mild conditions of 80°C and at a H₂ pressure of 0.5 MPa.Effectively,this serves as a model reaction for the upgrading of biomass and outperforms the performances of the constituent parts and that of the physical mixture[HSiW+Ru/UiO-66?Zr?].The highly dispersed Ru NPs act as active centers for hydrogenation,while the HSiW molecules possess Br?nsted acidic sites that cooperatively promote the subsequent lactonization of 4-HPME to generate GVL,and the UiO-66?Zr?crystal accelerates the mass transportation facilitated by its own porous structure with a large surface area.