Zeolitic imidazolate frameworks containing Zn as catalysts for the Knoevenagel condensation reaction

Zeolitic imidazolate frameworks (ZIFs) containing Zn(II) cations and 2-methylimidazolate anions were synthesized at high yield in aqueous medium. Triethylamine was used as an agent for deprotonation of the organic ligand, enabling rapid formation of the microporous structure known as ZIF-8. In the absence of the deprotonator, the material formed was ZIF-L, which has a lamellar structure. The ZIFs were characterized by X-ray diffraction, CO2 and N-2 physisorption, chloroform chemisorption, and scanning electron microscopy. The different amounts of triethylamine influenced not only ZIF structure, but also material characteristics as particle size and external area. The ZIFs were then evaluated as catalysts in the Knoevenagel condensation reaction, different catalytic performances were obtained depending on the amount of deprotonation agent used. The activation energy of ZIF-8 was estimated considering an irreversible pseudo-homogeneous first-order reaction, and was shown to be highly catalytically stable during consecutive reuses.

Automated summary

The synthesis of zeolitic imidazolate frameworks (ZIFs) in aqueous medium using Zn(II) cations and 2-methylimidazolate anions was studied, with triethylamine playing a key role in facilitating the formation of ZIF-8 microporous structure. The presence or absence of the deprotonation agent significantly affected the structure and characteristics of the ZIFs, impacting their catalytic performance in Knoevenagel condensation reaction.Furthermore, ZIF-8 exhibited high catalytic stability and lower activation energy during consecutive reuses.