Magnetic-responsive solid acid catalysts for esterification

Two kinds of magnetic-responsive solid acid catalysts were designed and prepared via an in situ polymerization of poly(ionic liquid)s (PILs) on the surface of Fe₃O₄@SiO₂ NPs for the catalyzed esterification of palmitic acid and methanol. They were characterized using XRD, TGA, VSM, NMR spectroscopy, FTIR spectroscopy, XPS, SEM, and GC techniques. The results confirmed the preparation of solid acid catalysts. Meanwhile, they possessed excellent catalytic activity and recyclability. The effect of the reaction conditions on the esterification was investigated through single-factor analyses, and the proposed catalytic mechanism of the prepared solid acid catalysts in the esterification are also discussed. Under the optimal reaction conditions (10 wt% catalyst, 6 h, 70 °C, and molar ratio (MR) of methanol to palmitic acid of 12 : 1), the conversion rate of palmitic acid could reach 94% and 79% with Fe₃O₄@SiO₂-poly(1-vinyl-3-ethylimidazolium phosphotungstate) (Fe₃O₄@SiO₂-P([VLIM]PW)) and Fe₃O₄@SiO₂-poly(1-vinylimidazole-3-propyl sulfonate) (Fe₃O₄@SiO₂-P([VLIM]SO₃)) NPs serving as catalysts, respectively. Furthermore, the Fe₃O₄@SiO₂-P([VLIM]PW) NPs could still maintain a high catalytic activity even after being reused 5 times without significant deactivation.