Synthesis And Catalytic Performance Of Nano-materials Derivedfrom ZIF-67

Zeolitic Imidazolate Frameworks(ZIFs) are a new class of surpramolecular microporous materials that have ordered networks formed by the self-assembly of inorganic metal cationsand nitrogen-containing organic bridging ligands. Owing to the characteristics of high specific surface areas and pore volumes, tunable pore sizes and functional structures, ZIFs have recently attracted continuously increasingresearch interest and have been used in various fields, such as gas separation and storage, drug delivery and catalysis.However, owing to the relatively low catalytic activity and stability of pristine ZIFs, it is extremely difficult to achieve major breakthrough in the field of catalysis. Therefore, the design and synthesis ofZIFs-derived catalysts with high catalytic efficiency and stability are still challenging.In this thesis, we aimed to develop novel and highly efficient ZIFs-based catalysts for some industrially important gas/liquid-phase oxidation and hydrogenation reactions byemploying ZIFs as sacrificialtemplatesand the structure-performance relationships were explored. The main contents of this thesisare as follows:Nanoscale Co-based carbon materials were prepared by simple thermolysis of a Co-containing metal–organic framework(MOF), ZIF-67, at different temperatures and their catalytic performance for low-temperature CO oxidation was evaluated. Co/C-600, which was obtained from ZIF-67 pyrolysis at 600 °C, exhibited high catalytic activity for CO oxidation even at a temperature as low as-30 °C. The calculated apparent activation energy of CO oxidation over the Co/C-600 catalyst was around 22 kJ mol-1. Moreover, the CO conversion remained unchanged at 100% after 24 h time on stream at room temperature, demonstrating good long-term stability. The results obtained after the introduction of moisture(H2O content, ~500 ppm) into the feed gas showed that the Co/C catalyst was tolerant of wet conditions, showing an unusual temperature-dependent catalytic behavior. Intensive investigation of the catalytic performance led to the conclusion that adsorption of H2 O molecules in the micropores of the catalyst caused this unusual catalytic behavior. This finding was supported by in situ FTIR spectroscopic experiments under both dry and wet conditions. Moreover, the catalytic activity of the Co/C material for CO oxidation could be fully recovered by mild heating treatment.In order to investigate therole of nitrogen doping in ZIF-derived materials, the application of nitrogen-doped carbon supported Co catalysts in selective hydrogenation of nitroarenes are described. The Co/C-N-600 materials were found to be highly efficient in the chemoselective hydrogenation of nitroarenes. A broad range of substituted nitroarenes are converted to the corresponding anilines in excellent yields under industrially viable conditions with other reducing groups remaining intact. In situ ATR-IR and XPS characterizations reveal that the Co-N centers present in the catalyst favor the preferential adsorption of nitro groups, leading to this unique chemoselectivity. The kinetic study indicates a zero-order dependence on 4-nitrostyrene while a first-order dependence on H2 pressure. A kinetic model is proposed based on the Langmuir-Hinshelwood kinetics as well as the experimental results. Due to their facile operation on synthesis, separation, and reutilization, the stable and cost-effective materials would hold the potential for broad applications in green and economical synthesis of fine chemicals.Metal-free nanocarbon catalysts have attracted much attention in recent years for their advantages of corrosion resistance, no heavy metal pollution and environmental friendliness as compared to metal-based catalysts. However, a facile preparation of heteroatom doped mesoporous carbon with a high catalytic efficiency is challenging. In this thesis,we report the development of a new kind of metal-free catalyst comprised of highly graphitized N-doped nanoporous carbons from direct carbonization of a metal–organic framework, i.e., ZIF-67. After metal etching, large specific surface areas and pore volumes, as well as high contents of sp2-bonded carbons are realized in the obtained carbons at the same time. As metal-free catalysts, these nitrogen-doped carbon materials exhibit excellent catalytic performances and robust stability in a series of oxidation reactions including aerobic oxidation of cyclohexane and toluene as well as oxidative coupling of amines. Systematic characterizations suggest that the accessible mesopores generated by chemical etching, and the homogeneous distribution of doped graphitic-type nitrogen should be responsible for the unprecedented performance of these carbon catalysts.