Direct and postsynthesis of tin-incorporated SBA-15 functionalized with sulfonic acid for efficient biodiesel production

Two types of sulfonic acid functionalized tin-incorporated SBA-15 mesoporous molecular sieves catalysts were prepared by the post functionalization method and one-pot functionalization method, which were designated as p-Sn-SBA-15-SO3H and o-Sn-SBA-15-SO3H, respectively. The catalysts were characterized by X-ray diffraction, FT-IR, nitrogen adsorption-desorption, pyridine-FTIR, thermogravimetric analysis, scanning electronic microscope and energy dispersive X-ray spectroscopy. The results demonstrated that tin and sulfonic acid were introduced into the framework of SBA-15 successfully for both catalysts, the structure and morphology of p-SnSBA- 15-SO3H was superior to that of o-Sn-SBA-15-SO3H. However, the experimental results showed that o-Sn-SBA-15-SO3H revealed a higher catalytic activity (conversion of 97.9%) than p-Sn-SBA-15-SO3H (conversion of 93.2%), due to the higher acidity of o-Sn-SBA-15-SO3H. It can be inferred that the catalytic performance was relative to both the structure and acidity of the catalyst, but the latter was a main factor in the catalytic system. The o-Sn-SBA-15-SO3H catalyst could still retain over 85.0% of conversion after 6 reaction cycles, indicating its good reusability and possibility of industrial applications.