Different Ligand Functionalized Al-Based MOFs as a Support for Impregnation of Heteropoly Acid for Efficient Esterification Reactions

The development of metal–organic frameworks (MOFs)–based heterogeneous catalysts with both Lewis acid and Brønsted acid sites has proved to be promising and useful because they offer an economical route to synthesize environment-friendly biofuels. Here, a series of Al-based MOFs, functionalized by single -H, -NH 2 , and -NO 2 groups, are successfully synthesized and applied as supports to load phosphomolybdic acid (HPMo) through a facile one-pot hydrothermal method, by forming composites of HPMo@Al-MOFs-X (where X = -H, -NH 2 , and -NO 2 ), and it was used to esterify fatty acids into biodiesel. The structural features of the prepared hybrid materials were evaluated by various techniques, including XRD, FTIR, BET, SEM-EDS, NH 3 -TPD, Py-FTIR, TG, and XPS. The material characterization revealed that the catalytic behavior of the prepared HPMo@AlB composite is better than HPMo@AlB-NH 2 , HPMo@AlB-NO 2 , and pure AlB. The optimized conversion of oleic acid (OA) is 97.5% under the optimized reaction conditions. Moreover, the composite maintained above 90% conversion after nine cycles and demonstrated excellent reusability. This outstanding catalytic activity and stability is mainly attributed to the large specific surface area (138.4 m 2 /g), appropriate pore volume (0.47 cm 3 /g), and mesoscale pore size (17.7 nm) of HPMo@AlB composite that reduced the mass transfer resistance, high total acidity, and the synergistic effect of Lewis acid and Brønsted acid sites and ensures efficient esterification. The present research introduces an important reference for advancing high-performance MOFs-based hybrid materials to industrialize biofuels production.