Direct synthesis of mesoporous sulfated silica-zirconia catalysts with high catalytic activity for biodiesel via esterification

A solid acid material of high loading of sulfated zirconia on mesoporous silica SBA-15 has been successfully synthesized by a direct-synthesis under strong acidic condition. The materials were characterized by powder X-ray diffraction, N₂ adsorption-desorption, UV-visible diffuse reflectance spectroscopy, transmission electron microscopy (TEM), ICP-mass, and NH ₃ temperature-programmed-desorption (TPD). The zirconia content and well-ordered mesostructure of SiO₂-SZ are controllable by tuning the molar ratios of sulfate to zirconia and silica to zirconia. UV-visible spectra and TEM observations confirm the incorporation of zirconium (IV) onto the mesoporoes framework. Acidity is enhanced in comparison with unsupported sulfated zirconia. Much improved catalytic performance under mild temperature condition in the esterification of lauric acid and palmitic acid with the direct-synthesis SiO₂-SZ catalyst was observed as compared to un-supported SZ. The good catalytic performance of the sulfated silica-zirconia materials is attributed to a higher dispersion of zirconia to give higher acid site density and also to better tolerance of water. The solid acid catalytic materials have many advantages over liquid acids in its environmentally friendliness and easy separation.