The enhanced activity of Ca/MgAl mixed oxide for transesterification

Abstract

Catalysts based on CaO/MgAl oxides were prepared by Ca(NO3)2.4H2O impregnation onto MgAl hydrotalcite followed by calcination at 600°C/0.5h. 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 4wt.% 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.