Moisture resistant K-loaded ZIF-8 catalyst for glycerol carbonate production

Zeolitic imidazolate frameworks (ZIFs) are a new subclass of metal-organic frameworks (MOFs) with a structure isomorphic to that of aluminosilicate zeolites. The zeolitic imidazolate framework-8 (ZIF-8) offered greater surface area and better hydrophobic properties, making it suitable for catalysis. The present study describes that ZIF-8 was synthesized in an aqueous solution by mixing 2-methylimidazole with Zn nitrate hexahydrate in deionized water. To enhance the basicity and performance of the ZIF-8 catalyst, a series of K-loaded ZIF-8 catalysts (K/ZIF-8) were prepared with varying amounts (5–10 wt%) of KOH content. Powder XRD, FTIR, XPS, HRTEM, TPD, and BET surface area measurement techniques have been used for structural and morphological characterization of the catalyst. The prepared K/ZIF-8 catalyst is employed as a heterogeneous catalyst to carry out glycerol (GL) valorization with dimethyl carbonate (DMC) to form glycerol carbonate (GLC). Various reaction parameters that affect the GLC yield, including DMC/GL molar ratio, KOH loading, catalyst amount, and temperature, have been studied during the reaction. Under the optimized reaction conditions of 10-K/ZIF-8 catalyst (5 wt% concerning GL), a DMC/GL M ratio of 3:1 in 0.5 h afforded up to 95 % GLC as an exclusive product. Even though the K metal ion is hygroscopic, the prepared catalyst demonstrated better water resistance (up to 4 wt% concerning GL) owing to organic group functionality. Moreover, the solid catalyst could be recycled up to three times without significantly decreasing activity.