Application of mesoporous sulfated MOF-808 catalyst supported on graphene oxide as a novel catalyst of biodiesel production process: Kinetic study and sensitivity analysis

Metal-organic framework (MOF)-based catalysts have become increasingly attractive for biodiesel production. Accordingly, MOF-808 was modified by sulfation with sulfuric acid to create a strongly acidic catalyst with enhanced performance for the esterification of oleic acid. To further tune the catalyst stability and kinetics, sulfated MOF-808 was grafted onto graphene oxide (GO), forming a MOF-808-SO 4 @GO composite. Catalysts' characterization analyses confirmed that sulfate groups were successfully introduced while MOF framework remained largely intact, resulting in an increase in both the strength and amount of acidic sites. Under optimal reaction conditions (120 °C, 3 h, methanol to oleic acid molar ratio of 30:1, and 5 wt% catalyst), MOF-808-SO 4 achieved a superior biodiesel yield of 93.25%, while the GO-based composite also showed high performance, reaching 85.62%. Kinetic studies showed that the reaction was well described by a pseudo-first-order model. Importantly, introducing GO lowered the activation energy from 17.03 kJ/mol for MOF-808-SO 4 to 13.17 kJ/mol for MOF-808-SO 4 @GO, indicating that GO support creates a more favorable kinetic environment by improving the accessibility of the acidic active sites. Reusability tests demonstrated that the composite catalyst exhibited superior stability and structural integrity resulting from strong interactions that GO formed with active catalytic species which prevented their leaching.