不同方法合成的沸石咪唑酯骨架结构材料(ZIF-8)的表征和催化性能

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

以二甲基咪唑为有机连接体和以Zn(OH)2或Zn(NO3)2·6H2O为Zn源,在甲醇与氨水的混合溶液、甲醇和DMF 3种不同的合成体系中合成了沸石咪唑酯骨架结构材料ZIF-8(分别记为ZIF-8(NH4OH)、ZIF-8(MeOH)和ZIF-8(DMF),并采用XRD、FTIR、N2吸附、SEM、TPD及Knoevenagel缩合反应等手段对所合成材料进行了表征。结果表明,采用这3种不同的合成方法均可成功制备出ZIF-8,所合成的ZIF-8的形貌基本一致,但其晶粒大小和酸碱性能有较大区别,同ZIF-8(NH4OH)和ZIF-8(DMF)相比,ZIF-8(MeOH)晶粒分布集中、平均粒径较小且具有较大的外比表面积和较多的酸碱位。不同方法合成的ZIF-8在苯甲醛和丙二腈的Knoevenagel缩合反应中的催化性能有很大差异,ZIF-8(MeOH)催化活性明显高于ZIF-8(DMF)和ZIF-8(NH4OH),其较高的催化活性,同其较大的外比表面积和酸碱性能密切相关。

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）2 or 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.