4. Conclusion
We developed new powerful heterogenized Brønsted acid catalysts via a new route of immobilization of ionic liquids onto silica surface. By the electrostatic immobilization, the obtained catalysts with the loosely movement of the supported imidazolium cation, as a molecular catalyst, in the reaction medium makes the catalysts to possess both the advantages of homogeneous and heterogeneous ones. The prepared catalysts displayed strongly reasonable catalytic behavior with relative stability at mild temperature (130oC) and stoichiometric ratio (OA: TMP = 3:1) in direct esterification of OA with TMP for production of bio-degradable lubricant.