Catalytic Properties Based On Zeolitic Imidazolate Framework-8

Zeolitic imidazolate frameworks (ZIFs) are a new subclass of metal-organic frameworks (MOFs) comprised of ordered networks which are formed by imidazole or imidazole derivatives and inorganic transition metal cations (Zn/Co). ZIFs possess highly desirable properties of both conventional zeolites and MOFs. ZIFs have been emerging as very promising functional materials for gas adsorption, separation and catalysis due to their tunable porosity, large surface areas, high thermal and chemical stabilities. The ZIF-8framework, a typical representative of ZIFs, has potential applications in catalysis. It can be used as heterogeneous catalyst or catalytic support owing to its high thermal stability and surface area, unique pore structure and surface acid-base properties.However, research works have been mostly focused on synthesis of new ZIFs and their applications in gas adsorption, separation and storage, and the reports on their catalytic application have been scarce. In this paper, the utilization of ZIF-8as heterogeneous catalyst or catalytic support was investigated. It is ecpected that this work can provide the theoretic and practical foundation for the application of ZIF-8in the catalysis field. 1) Characterization and catalytic performence of ZIF-8synthesized by different methodsA series of zeolitic imidazolate framework-8(ZIF-8) samples was synthesized in a mixture of methanol and aqueous ammonia, methanol, and DMF, respectively (denoted as ZIF-8(NH4OH), ZIF-8(MeOH) and ZIF-8(DMF)) with2-methylimidazole as an organic linker and Zn(OH)2or Zn(NO3)2·6H2O as Zn source. The physicochemical properties and catalytic performance of the samples were characterized by XRD, FTIR, N2adsorption, SEM, TPD and Knoevenagel reaction. The results show that ZIF-8can be synthesized by three methods and the samples synthesized by different methods have similar morphologies, but different particle sizes and acid-base properties. ZIF-8(MeOH) has much narrower particle size distribution, smaller particle size as well as more acid and base centers than those of ZIF-8(NH4OH) and ZIF-8(DMF). The ZIF-8samples exhibit significant differences in catalytic performance for Knoevenagel reaction from benzaldehyde and malononitrile. ZIF-8(MeOH) is the most effective catalyst. The higher catalytic activity of the ZIF-8(MeOH) sample is closely related with its higher external surface area and acid-base properties.2) Ru/ZIF-8with a chiral modifier for asymmetric hydrogenation of acetophenoneA series of Ru/ZIF-8catalysts was prepared in the different impregnation solvents and characterized by ICP, XRD, TEM, and N2adsorption. The obtained catalysts exhibited different catalytic performances in the presence of achiral modifier triphenylphosphine (TPP) and chiral modifier (1S,2S)-1,2-diphenylethylenediamine [(1S,2S)-DPEN] for asymmetric hydrogenation of acetophenone. The impregnation solvents have great influences on the catalytic performances of the prepared Ru/ZIF-8catalysts. Ethanol was found to be the most effective impregnation solvent, while low activity and enantioselectivity were observed for water. The prepared Ru/ZIF-8catalyst was stable and could be reused at least five times without significant loss in activity and entantioselectivity.3) Pd/ZIF-8as an efficient heterogeneous catalyst for the selective hydrogenation of cinnamaldehydePalladium nanoparticles supported on ZIF-8(Pd/ZIF-8) are employed as an efficient heterogeneous catalyst for the selective hydrogenation of cinnamaldehyde. The catalyst was characterized by XRD and N2adsorption. The results show that Pd/ZIF-8exhibited excellent catalytic performance for the selective hydrogenation of cinnamaldehyde. The reaction solvents have great influences on the catalytic performances of the prepared Pd/ZIF-8catalysts. The Pd nanoparticles supported on ZIF-8exhibits much higher catalytic activity and hydrocinnamaldehyde selectivity than those supported on other MOFs or inorganic-matrixes. The prepared Pd/ZIF-8catalyst was stable and could be reused at least five times without significant loss in activity and selectivity.