Characterization and Catalytic Performence of Zeolitic Imidazolate Framework-8(ZIF-8) Synthesized by Different Methods

A 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)) with 2-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, N2 adsorption, SEM, TPD and Knoevenagel reaction. The results show that ZIF-8 can 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-8 samples exhibit significant difference 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.