The enhanced activity of Ca/MgAl mixed oxide for transesterification

• Calcium containing oxides for catalytic transesterification
• The Ca addition onto MgAl mixed oxide increases the base site strength.
• 40-Ca/MgAl exhibited higher activity than commercial CaO.
• The Ca/MgAl catalysts could be reused for several batch runs.
• The reaction occurs through a heterogeneous mechanism.

Catalysts based on CaO/MgAl oxides were prepared by Ca(NO3)2.4H2O impregnation onto MgAl hydrotalcite followed by calcination at 600 °C/0.5 h. The materials were characterized by means of XRD, N2 physisorption, FEG-SEM equipped with energy-dispersive X-ray spectroscopy (EDS) and TPD of CO2. The oxide reactivities were evaluated using the model transesterification reaction between methyl acetate and ethanol under mild reaction conditions (50 °C, ethanol/methyl acetate molar ratio = 6/1 and 4 wt.% of catalyst). MgAl mixed oxide was inactive for transesterification. On the other hand, the Ca addition onto the oxides considerably increased the base site amounts and strengths of the Ca/MgAl, greatly improving their catalytic performances. Remarkably high conversions were obtained for 40-Ca/MgAl compared to commercial CaO. Thus, the CaO dispersion over MgAl mixed oxide showed to significantly improve the catalytic performance of CaO. Stability tests revealed that the Ca/MgAl can be reused for at least 5 reaction cycles and the reaction occurs through a heterogeneous process. Due to the high activity, this type of catalyst can be pointed as a promising heterogeneous catalyst for biodiesel production although the Ca leaching must be formerly resolved for practical use.