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 features a bio-renewable linker (furan-2,5-dicarboxylic acid) and can be obtained through a green synthesis. In this work, we report an optimized synthesis of CAU-28, substantially enhancing the yield from 2 to 53 %. Moreover, taking advantage of the high thermal and chemical stability of CAU-28 as well as the MOF's surface area (> 1000 m2 g-1), porosity, and four open metal sites per Zr6-cluster, we have demonstrated 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.