A Zirconium-based Metal–Organic Framework as an Effective Green Catalyst for the Synthesis of Biodiesel

CAU-28 (CAU = Christian-Albrechts-University) is a zirconium-based metal–organic framework (MOF) that was first dis-covered in 2017. In addition to its biorenewable linker and green synthesis, which uses a microwave for only 2 hours, this MOF also features high thermal and chemical stability, surface area, and porosity. The hexanuclear zirconium clusters in CAU-28 are connected to only eight furan-2,5-dicarboxylic acid linkers, resulting in four open metal sites per cluster. These open metal sites display Lewis acidic properties and can be taken advantage of for many applications, including catalysis. In this work, we demonstrate the high potential of CAU-28 as a green catalyst to produce biodiesel through esterification reactions. Under optimized catalytic conditions, CAU-28 is able to convert oleic acid to its fatty acid methyl ester counterpart with high selectivity, using a catalyst loading of only 5 wt.% and 1:24 molar ratio of oleic acid:methanol, at 90 °C for 90 min. Furthermore, the catalyst also shows high stability, maintaining its activity for three reaction cycles.