DBU-assisted expeditious synthesis of highly stable IL@ZIFs intergrowth composite: A nanocatalyst for EMC production

• DBU can overcome the slow kinetics of nucleation and crystallization of zeolitic imidazolate framework. • In the rapid crystallization process, DBU functions as a template and inducer, and remains in the framework. • The DBU-PO@ZIF-8 composite show a high catalytic activity for synthesizing EMC by transesterification. • The catalytic mechanism of DBU-PO@ZIF-8 in the transesterification was explored and revealed. Methyl ethyl carbonate (EMC) is the primary raw material for the electrolyte of lithium-ion batteries. It is mainly prepared by the transesterification reaction of dimethyl carbonate (DMC) and EtOH. However, homogeneous alkaline catalysts such as sodium alcohol commonly used in industry are easy to deactivate and challenging to separate and recover. Therefore, the alkaline ionic liquid decorated zeolitic imidazolate frameworks (IL@ZIFs) heterogeneous catalysts were prepared using a simple method with DBU as an inducer. In the synthetic route of IL@ZIFs, the ligand of ZIFs can form an ionic liquid with DBU, and deprotonated ligands will rapidly coordinate with metal ions at room temperature. The DBU can also play the structural guidance and stabilizer, which is conducive to the rapid and effective preparation of ZIFs materials. Meanwhile, the DBU, which has a large molecular diameter, will be trapped in the pore cage and can combine with other protic materials (imidazole, triazole, 2-methylimidazole, phenol, etc.) to form alkaline ionic liquids. The prepared DBU-IL@ZIFs were used as heterogeneous catalysts for synthesizing EMC by transesterification reaction. The DBU-PO@ZIF-8 composite with phenol as anion has better catalytic activity. Under the appropriate reaction conditions, the yield of EMC can reach 55.7% with high selectivity of 94.7%. The catalytic mechanism of DBU-PO@ZIF-8 in the transesterification reaction was also explored and revealed.