Preparation, characterization and application of a novel solid Brönsted acid catalyst SO42−/La3+/C for biodiesel production via esterification of oleic acid and methanol

The central S atom of the SO3H group was existed in the form of sp3 hybridorbital, this will lead the SO42− to be coordinated with La3+ in the form of four-coordination bond. The SO double bond in the SO42− group will exert a strong electron-withdrawing function when SO42− was existed in the form of coordination bond. The intensity of electrostatic field will be increased more when SO42-was four-coordinated with La3+. Along with the rising of magnitude of electrostatic field, the COH oxygen of the carboxyl group (SP2 hybridised) that were present at the end of the carbon carrier and H2O also will be more easier to form a coordination bond with SO42−/La3+. Correspondingly, a six-coordination bond was formed from the interaction of SO42−/La3+, COH oxygen of the carboxyl group and H2O. Hence, H2O will not reduce the concentration of Brönsted acid of SO42−/La3+/C catalyst. On the contrary, H2O can improve its concentration of Brönsted acid and catalytic stability.66