Here, we demonstrate the utilization of calcined jackfruit seeds as highly efficient heterogeneous base catalysts (JSC-400 and JSC-600) for biodiesel synthesis from soybean oil. Catalysts were characterized by PXRD, FTIR, \({\text{N}}_{2}\) -adsorption, SEM–EDX, FETEM, XPS, Hammett and CO2-TPD techniques. PXRD and FETEM analysis confirmed the presence of mixed metals in their oxide and carbonate forms, and their polycrystalline structures, respectively. FESEM and \({\text{N}}_{2}\) -adsorption revealed the spongy, flake-like morphology and mesoporous structure of the catalysts. The concentration of potassium (K) in JSC-400, which is responsible for its basicity, was evaluated using EDX (12.40 atomic%) and XPS (13.87 atomic%). JSC-400 showed a more promising biodiesel yield (97.7%) in 30 min, which might be due to the higher basicities of JSC-400 with 11.51, 0.42 mmol/g and 1.997 mmol/g than JSC-600 (11.51, 0.42 mmol/g and 1.997 mmol/g) as measured by pH, Hammett and TPD-CO2 techniques, respectively. Three times consecutive recycle study of JSC-400, showed no significant loss in yield (95.2%), compared to fresh catalyst (97.7%). Thermodynamic and kinetic studies confirmed the non-spontaneous and pseudo-first order reaction, respectively. Product was confirmed by FTIR, 1H and 13C NMR and GC–MS techniques, and fuel properties were found to be comparable with the literatures and international standards.
