The Catalytic Applications Of Metal-organic Frameworks Materials

Metal Organic Frameworks (MOFs) are a type of porous materials that composed of metal ions or metal clusters connected by organic ligands. Due to the characteristics of high surface area and large internal pore volume, highly dispersed metals ions, post-synthesis modification, MOFs can be applied in gas adsorption, drug delivery, molecular reactions, and catalytic reactions. However, the application of MOFs in catalysis is still in an initial stage. The MOFs and related materials are still rarely used in traditional catalytic reactions. Now improving the catalytic activity of MOFs catalytic materials and exploring their new catalytic application is a difficult and hot spot in the catalytic field. In this paper, on the one hand, MOFs were functionalized by the post-synthesis modification method, and then loaded with coordination compound catalysts via the chelating method; meanwhile, highly dispersed metal nanoparticles were immobilized on MOFs at nanoscale to prepare the supported catalyst; On the other hand, MOFs as heterogeneous catalysts were directly used in catalytic reactions. The obtained catalysts were investigated in the catalytic application, and the relationship between their structures and properties was also discussed. The studies provide theoretical and experimental foundation for the practical application of MOFs. The work is divided into three parts as follows.(1) Efficient Mo(VI) modified Zr-MOF catalysts have been successfully prepared for the epoxidation of olefins. The stable and porous Zr-MOF (UiO-66(NH2)) material was modified by the post-synthesis modification (PSM) method and then the Mo based catalysts were loaded by a chelating method. The MOFs not only act as the carriers of the Mo(VI) catalyst, but also improve the contacting ability between the substrate and the active center of the Mo(VI) compound. The high dispersion of the Mo catalyst on Zr-MOF and the big pore size of MOF guarantee the substrates contacting with catalytic active center, sufficiently, thus accelerating the reaction speed and providing improved catalytic efficiency for the epoxidation of olefins.(2) Highly dispersed Au nanoparticles have been immobilized on the amino-functionalized metal-organic framework (UiO-66(NH2)). The amino-functionality on MOF is employed for a rapid absorption of HAuCl4, which acts as the gold (0) precursor in the absence of protecting agent. The resulting Au@MOF catalyst via solution-based synthesis exhibited high catalytic activities towards the reduction of 4-nitrophenol and aerobic oxidation of alcohols under ambient conditions. The facile synthetic approach opens up an alternative route for the metal nanoparticles on MOF catalysts under mild condition.(3) The highly porous metal-organic framework (Fe-MIL-101) was used as a heterogeneous catalyst for the acetalization of aldehydes, paal-knorr reaction, and four-component coupling reactions. The highly dispersed Fe(Ⅲ) ions, large surface area, and big pore size of Fe-MIL-101 contribute to offering an access for organic substrates to the active sites sufficiently, which ensure a high catalytic performance of Fe-MIL-101. The Fe-MIL-101 catalyst can be used multiple times without asignificant decrease in activity, which indicates the high stability of Fe-MIL-101 under the reaction conditions.