Sulfated titania [TiO2/SO42−]: A very active solid acid catalyst for the esterification of free fatty acids with ethanol

Sulfated titanias were prepared by using ammonium sulfate and sulfuric acid as sulfate precursors. Depending on the sulfation method, important effects on the acidity, textural properties as well as on activity were found. After ammonium sulfate was used, a large amount of SO linked to the titania surface was observed by FTIR spectroscopy. The acidity strength determined with Hammett indicators showed strong acidity in the sulfated samples. The FTIR-pyridine adsorption spectra evidenced the presence of Lewis and Brönsted acid sites in the catalysts sulfated with ammonium sulfate, while in the titania sulfated with sulfuric acid, only Lewis-type sites were observed. The sulfated titanias showed very high activity for the esterification of fatty acids with ethanol in a mixture of oleic acid (79%). Conversions up to 82.2% of the oleic acid and selectivity to ester of 100% were reached after 3 h of reaction at 80 °C. The results showed that sulfated titanias are promising solid acid catalysts to be used in the esterification of free fatty acids with ethanol.

In depending on the sulfation method, important effects on the acidity, textural properties as well as on the activity for the esterification of fatty acids with ethanol. Conversions up to 82.2% of the oleic acid and selectivity to ester of 100% were reached after 3 h of reaction at 80 °C in sulfated titania: (▾) titania impregnated with ammonium sulfate; (♦) titania sol–gel sulfated with ammonium sulfate; (▴) titania sol–gel sulfate with sulfuric acid; (●) titania sol–gel; (■) without catalyst.Figure optionsDownload high-quality image (71 K)Download as PowerPoint slide