Facile Synthesis of Silver‐Exchanged Phosphotungstic Acid Immobilized on Sn‐Bi Bimetallic Metal–Organic Frameworks for Enhanced Esterification

Abstract

Metal–organic frameworks (MOFs) are ideal supports for the synthesis of porous composite catalysts. In the present study, Sn‐Bi bimetallic metal–organic frameworks (Sn‐Bi‐MOFs) supported silver‐doped phosphotungstic acid (AgPW) catalysts (AgPW@Sn‐Bi‐BDC and AgPW@Sn‐Bi‐BDC (NH2)) were successfully synthesized via a simple in situ impregnation method, which was subsequently applied to catalyze esterification for the production of biodiesel from oleic acid (OA). The physico‐chemical properties of the prepared composite catalysts underwent comprehensive analysis through XRD, FTIR, N2 physisorption, SEM, EDX, NH3‐TPD, Py‐FTIR, TG, and XPS techniques, confirming the successful impregnation of AgPW on the Sn‐Bi‐MOFs framework. Among the catalysts tested, AgPW@Sn‐Bi‐BDC (NH2) exhibited the better catalytic activity than that of Sn‐Bi‐BDC, Sn‐Bi‐BDC (NH2), and AgPW@Sn‐Bi‐BDC, reaching 91.6% of OA conversion with the methanol:OA molar ratio of 20:1 and the catalyst quantity of 0.2 g at 130°C for 4 h. The high activity of AgPW@Sn‐Bi‐BDC (NH2) is attributed to the available multiscale pore structure, high acidity, and the synergistic action of the Brønsted and Lewis acidic sites. Additionally, the esterification with AgPW@Sn‐Bi‐BDC (NH2) followed the first‐order reaction kinetic model, with an Ea of 34.5 kJ/mol. Moreover, the recyclability of the composites was also assessed, demonstrating sustained catalytic activity after four reuses. This approach showed a potential for sustainable and efficient energy production through bimetallic MOFs‐based composite catalysts.