Modification Of Metal-Organic Framework MIL-101 And Their Catalytic Applications

Metal-organic frameworks?MOFs?,emerging as a new class of crystalline porous materials formed by self-assembling of metal ions/metal clusters and organic ligands,have attracted extensive interest in recent years.MOFs exhibited excellent performances in a variety of applications,especially in catalysis due to their highly ordered porous structure and tailorability.The highly porous structure of MOFs can facilitate the transport of substrates/products and guarantee the accessibility of catalytic active sites.The well-defined and tailorable crystalline structures of MOFs make them be an ideal platform for the establishment of clear structure-property relationships.Considering the limited types of active sites of the pristine MOFs,in order to further expand the catalytic application range of MOFs and further improve their catalytic performances,this thesis focuses on the introduction of active components into MOFs to build multifunctional composite materials and the utilization of MOFs as precursors to prepare porous metal oxides.The controllable preparation,structure characterization,material formation mechanism and catalytic performance of these materials were also studied,and the synergistic effects between the host and the object were discussed.The main research result are as follows:A general synthesis approach for the encapsulation of ultrafine alloyed nanoparticles?NPs?with high loadings in the pores of MOFs was developed.In this study,for the first time we proposed a facile and general strategy to immobilize ultrafine alloyed NPs within the pores of a MOF by the galvanic replacement of transition metal NPs?e.g.,Cu,Co,and Ni?with noble metal ions?e.g.,Pd,Ru,and Pt?under high-intensity ultrasound irradiation.Nine types of bimetallic alloyed NPs of base and noble metals were successfully prepared and immobilized in the pores of MIL-101 as a model host,which showed highly-dispersed and well-alloyed properties with average particle sizes ranging from 1.1 to 2.2 nm and high loadings of up to 10.4 wt%.At the same time,the properties of the resultant alloyed NPs can be finely tuned by the ultrasound intensity,ultrasound irradiation time,transition metal loadings and the added amounts of noble metal ions.Benefitting from the ultrafine particle size and high dispersity of Cu-Pd NPs and especially the positive synergy between Cu and Pd metals,the optimized Cu-Pd@MIL-101 exhibited extremely high activity for the homocoupling reaction of phenylacetylene under unprecedented base-and additive-free condition and room temperature,affording at least 19 times higher yield?98%?of1,4-diphenylbuta-1,3-diyne than its monometallic counterparts.In order to further improve the catalytic activity,a simple and novel strategy was developed for the synthesis of hierarchical materials,enabling the as-prepared catalysts to show both hierarchical pores and multi-functional active sites.We proposed a novel strategy for enlarging the pore sizes of MOFs throughout the ionic liquids@MOF?ILs@MOF?composites by thermal transformation.The obtained N-doped nanocarbon@quasi-MOF materials?CN_x@quasi-MOF?not only possessed in-situ formed mesopores,but also achieved multi-active sites without the sacrifice of their structure stability.Thus,the as-fabricated CN_x@quasi-MIL-101 could efficiently facilitate the mass diffusion,exhibiting as high as 96%yield for the synthesis of 4-???9H-carbazol-4-yl?oxy?methyl?-1,3-dioxolan-2-one?4-CDO?from 4-?2,3-Epoxypropoxy?carbazole?4-EPC?and CO₂ under mild?90°C and ambient CO₂pressure?and co-catalyst-free conditions.Furthermore,Fourier transform infrared spectroscopic investigations confirmed the strong interaction between the unsaturated Cr-site in the materials and CO₂.Pyridine adsorption experiments demonstrated the strong Lewis acidity of the materials.Both the strong interaction and Lewis aciditiy led to the superior catalytic performances.A "bottom-up strategy" with confined pyrolysis assisted was developed to achieve highly-dispersed metal oxide materials by using Si O₂@MIL-101,the as-prepared material greatly reduced the agglomeration of metal oxide NPs.MOF-derived porous metal oxides could inherit some advantages of MOFs while exhibiting new catalytic features.On the other hand,the facile fabrication of porous solid acids is highly desired for replacing the hazardous liquid acids for many acid-catalyzed reactions in the chemical industry.Herein,we present a bottom-up strategy to construct ultra-stable mesoporous Cr Si O_x nanohybrids with highly-dispersed Lewis acid sites by pyrolysis of Si O₂@MIL-101 precursor prepared via nanocasting by a reverse double-solvents approach,which can guarantee the efficient encapsulation of Si O₂ NPs inside the MIL-101 pores.Pyridine adsorption experiments demonstrated that the density of Lewis acidic sites in the obtained Cr Si O_x nanohybrids was much higher than that of MIL-101-derived Cr₂O₃ NPs.Benefitting from its highly-mesoporous nanostructure with abundant acidic sites,the optimal Cr Si O_x?19%,600°C?exhibited a significantly improved catalytic activity for the Lewis-acid-catalyzed Meerwein-Ponndorf-Verley reduction of cyclohexanone with 4.5 times higher yield of cyclohexanol than that of the MIL-101-derived Cr₂O₃ NPs,representing the first efficient Cr₂O₃-based catalytic system for this reaction.