Green synthesis of SiO 2 -immobilized acidic ionic liquids via thiol-ene click chemistry for efficient biodiesel production

Solid-immobilized acidic ionic liquids have emerged as promising catalysts for biodiesel production via esterification of vegetable oils and/or animal fats. However, the preparation of such catalysts typically involves hazardous organic solvents and heavy metal catalysts, and requires elevated reaction temperatures. In this study, we report a green, mild, and heavy-metal-free strategy to synthesize a novel SiO 2 -immobilized acidic ionic liquid (SiO 2 -AIL) catalyst via the Stöber method, followed by in-situ thiol functionalization and a thiol-ene click reaction. Characterizations confirmed the successful structural grafting and high thermal stability of the as-prepared catalyst. In the esterification of oleic acid with methanol, the SiO 2 -AIL demonstrated exceptional catalytic performance, achieving a maximum conversion of 95.5% under optimized conditions (60°C, 5 h, methanol/oleic acid molar ratio of 12:1, and catalyst loading of 9 wt%). The esterification followed pseudo-first-order kinetics with a remarkably low activation energy of 39.04 kJ/mol. Additionally, the catalyst exhibited excellent reusability (conversion = 77.4% after five cycles). This study provides a sustainable and efficient pathway for designing highly active, recyclable solid acid catalysts for biodiesel production.