Synthesis And Catalytic Performance Of Composite Materials Derived From Nitrogen Contaning MOFs

Metal-organic frameworks(MOFs) are a new class of surpramolecular microporous materials that have ordered networks formed by the self-assembly of organic bridging ligands and inorganic metal cations. There has been substantial interest in the areas of gas sorption and separation, drug delivery, biological-imaging, sensors, devices and catalysis due to the outstanding surface properties and tunable structure of MOFs. However, in the field of catalysis, it is extremely difficult to achieve major breakthrough owing to the relatively low catalytic activity and stability of pristine MOFs. Therefore, the design and synthesis of MOFs-derived catalysts with high catalytic efficiency and stability are still challenging.Considering that N-doped porous materials could exhibit unique electronic properties, and have a strong interaction with the doped metal and species, a series of MOF-derived catalysts have been developed via post-modification of nitrogen-containing MOFs with metal species, and also pyrolysis of nitrogen-containing MOFs to obtain N-doped carbon embedded metal nanomaterials. Their catalytic performances were investigated in detail in green synthesis reactions and the structure-performance relationships were explored. The main contents and experimental results of this thesis are as follows:A novel Pd(II)@MOF catalyst was prepared by a simple method. Heterogenization of the homogeneous palladium species was achieved by using Zr MOF-BIPY(Zr6O4(OH)4(bpydc)6, bpydc = 2,2’-bipyridine-5,5’-dicarboxylate) as support, which featured uncoordinated bpy moieties in the MOF framework. Pd(II)@MOF was shown to be highly efficient for the carbonylative Sonogashira coupling reaction of aryl iodides with terminal alkynes to afford the corresponding aryl α,β-alkynyl ketones with a broad substrate tolerance without the addition of any phosphine ligands. The catalyst could efficiently promote the carbonylative coupling reaction under atmospheric pressure of CO. Moreover, this heterogeneous catalyst was stable and recoverable, which could be reused at least five times without any significant loss in catalytic efficiency and selectivity and showed negligible metal leaching. The combination of high catalytic efficiency and substrate compatibility as well as good recyclability provides a practical and environmentally friendly procedure for the preparation of ynones.Metal loading on N-doped carbon has shown high catalytic performance due to the unique electronicproperties and high stablility of the N-doped carbon matrix. In this thesis, we reported a new strategy to synthesize Co@C-N materials by thermal decomposition of a nitrogen-containing MOF. The small Co nanoparticles embedded in the N-doped carbons were highly dispersed. We proposed the use of MOFs containing mixed ligands to control C/N ratio of the obtained materials, which could significantly affect the performance of the nitrogen-doped materials. The Co nanoparticles were still highly dispersed even with high Co contents of ca. 30-45 wt% in the porous carbon matrices. The as-prepared Co@C-N composites exhibited an outstanding performance in the aerobic oxidation of secondary alcohols, with significantly improved catalytic activities as compared to the N-free Co@C synthesized using the traditional impregnation method and also by themolysis of N-free MOF materials. Without the addition of bases, Co@C-N700 showed high activity in the oxidation of secondary alcohols in water under air.Amides are inarguably among the most abundant motifs that are found in biological activities, natural products, pharmaceuticals, and synthetic intermediates. However, the traditional one-step amidation methods are always associated with series limitations such as low selectivity, and harsh reaction conditions. We have developed a novel synthesis strategy for amides by oxidative amidation of aldehydes using a heterogeneous Co-based catalyst. The material is highly active in oxidative amidation of a wide range of aldehydes with DMF, affording the corresponding amides in up to 96% yields under mild conditions. Interestingly, the cobalt-based material could be easily separated from the solution after reaction by using an external magnetic field. Furthermore, the catalyst was reusable and retained high catalytic activity even after recycling for a number of times. Mechanistic studies indicated the reaction proceeded via radicals under mild conditions, which mainly included three reaction steps. First, the tert-butoxyl and tert-butylperoxyl radicals were generated with the assistance of the cobalt-based catalyst. Next, these radicals abstracted hydrogen from the aldehyde and DMF to form acyl radical and aminyl radical, respectively. Finally, cross-coupling of the radicals led to the production of the corresponding amide. This work would provide an alternative and environmentally benign methodology for the synthesis of amides.