Assessment the activity of magnetic KOH/Fe₃O₄@Al₂O₃ core-shell nanocatalyst in transesterification reaction: effect of Fe/Al ratio on structural and performance

Recently, biodiesel production using heterogeneous catalysts has been of great concern. However, simple separation of these catalysts from product mixtures is a problem of the process. In this study, series of magnetic KOH/Fe₃O₄@Al₂O₃ core-shell nanocatalysts were synthesized via the incipient wetness impregnation method and the effect of weight ratio of Fe₃O₄-to-Al₂O₃ (0.15-0.35) on the catalytic performance was assessed. The samples were characterized by XRD, FTIR, BET-BJH, VSM, SEM, TEM, and EDX analyses and their basicity was measured by the Hammett indicator method. The results revealed that although the magnetic KOH/Fe₃O₄@Al₂O₃ nanocatalyst with 25 wt% of Fe₃O₄ showed less activity as compared to those with 15 wt% of Fe3O4, it exhibited higher surface area and appropriate magnetic properties. The sample presented superparamagnetic properties with the magnetic strength of 1.25 emu/g that was simply recovered by using an external magnetic field. The nanocatalyst converted 98.8% of canola oil to biodiesel under reflux condition at the best operational conditions of 12 M ratio of methanol/oil, 4 wt% of catalyst and 6 h of reaction time. Moreover, the nanocatalyst showed high reusability such that it was reused several times without appreciable loss of its catalytic activity.