The enhanced activity of base metal modified MgAl mixed oxides from sol-gel hydrotalcite for ethylic transesterification

Abstract

MgAl hydrotalcite was successfully prepared through the sol-gel method and modified by in situ addition of base metals (Me = K, Ba, Sr and La). The Me–MgAl hydrotalcites were calcined and the obtained oxides were evaluated as catalysts for ethylic transesterification in order to investigate their potential application for biodiesel production. The Me–MgAl characterization revealed that the materials present different crystalline structures and the metal addition caused surface area reduction and increased the apparent crystallite size. On the other hand, the addition of the base metals to hydrotalcite deeply affected the base properties of the oxides, increasing their catalytic activity. Particularly, the Ba–MgAl presents the highest amount of strong base sites which resulted in a high conversion (≈90%) in the model transesterification reaction between methyl acetate and ethanol. Furthermore, an ester conversion of about 80% was reached in soybean oil transesterification. Moreover, the Ba–MgAl can be reused for 3 batch cycles with low deactivation. These results suggest that Ba–MgAl can be considered a promising heterogeneous catalyst for biodiesel production.