Controlled Growth Of Monodisperse Ferrite Octahedral Nanocrystals For Biomass-derive Catalytic Applications

Metal-organic frameworks?MOFs?are a new class of porous functional materials.In recent years,the use of MOFs as sacrificial template to generate metal or metal oxide/C composite materials has attracted extensive interest.However,most of the metal-based materials derived from MOFs showed a broad distribution of particle size and irregular shape.How to the preparation of metal nanoparticles with uniform size and shape from MOFs thermolysis remains a great challenge.In this thesis,Fe-MIL-88 B,used as the sacrificial template,was pyrolyzed at high temperatures under the mixed atmosphere of Ar+CO.The morphology,composition and structure of the obtained materials were thoroughly characterized by transmission electron microscopy?TEM?,N2 adsorption/desorption,powder X-ray diffraction?PXRD?,X-ray photoelectron spectroscopy?XPS?,Raman spectroscopy?Raman?,temperature-program desorption?TPD?,thermogravimetric analyzer?TG?,atomic absorption spectrometer?AAS?,ATR infrared spectrometer?ATR-IR?.The results showed that the generated materials were composed of Fe₃O₄ nanoparticles and C?denoted as FeO_x/C?.When the MOF precursor was pyrolyzed in pure Ar atmosphere,highly aggregated Fe₃O₄ nanoparticles with irregular shape were observed.With the introduction of CO,the morphology of the Fe₃O₄ nanoparticles gradually became regular,and uniform Fe₃O₄ octahedra with only?111?facets exposed were obtained when the gas concentration of CO and Ar was 1:1.In order to investigate the intrinsic effect of CO on the materials preparation,density functional theory calculation was performed to obtain the adsorption energies of CO with the Fe₃O₄?111?facets and Fe₃O₄?100?facets,respectively.Combing with the CO oxidaton resuls on the FeO_x/C materials,it was found that CO was more prone to adsorb on the Fe₃O₄?111?facets than Fe₃O₄?100?facets.As the shape of Fe₃O₄ is depended on the growth rate of?100?facet and?111?facets,it was suggested that the preferential adsorption of CO on the?111?facets could affect their growth rate that subsequently control the morphology of the crystals.FeO_X/C materials were also tested as catalysts in the selective oxidation of biomass-derived 5-hydroxymethylfurfural?HMF?to 2,5-diformylfuran?DFF?.HMF is composed of a hydroxyl and a carbonyl compound,both the hydroxyl and carbonyl groups can be oxidized in the oxidation process,which makes the selective oxidation to a single product of DFF difficult.In this work,the HMF conversion and DFF selectivity were both 99% when using the material obtained in the atmosphere of Vco/VAr=1.This result was much higher than the catalyst with irregular shape which was perpared under pure Ar?the HMF conversion was 18% with 33% selectivity of DFF?.The results of ATR-IR and DFT calculation indicated a stronger adsorption of the –OH bond in HMF present on the?111?facets as compared to the C=O bond,which may account for the significantly improved activity and selectivity.