Catalytic evaluation of ZnAl₂O₄ and ZnAl_1.9Eu_0.1O₄ spinels in the methanol transesterification of soybean oil

This study aimed to evaluate the effect of Eu doping on the structure and morphology of the ZnAl_1.9Eu_0.1O₄ spinel and its performance as catalyst in methyl transesterification of soybean oil. The catalyst materials were synthesized by the combustion reaction and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy and thermogravimetric analysis. The transesterification reactions were conducted at 160 and 180 ºC, oil:alcohol molar ratio 1:15, 2% of catalyst and time reaction 3 h. The XRD and FTIR results indicate the presence of the aluminate spinel phase and two absorption bands between 450 and 700 cm^-1, characteristic of the spinel structure. The results of transesterification reactions showed that doping ZnAl₂O₄ with 0.1 mol of europium promoted an increase in the catalytic conversion (15.8% to 68.7%), indicating that europium turns the catalyst more active. Increasing the reaction temperature from 120 to 180 ºC caused a considerable increase in the catalytic conversion of 18.4 to 68.7% using the catalyst doped with europium. The conversion of the reused catalyst ZnAl_1.9Eu_0.1O₄ showed a reduction of 31% when used for the third time.

combustion; alcoholysis; aluminate zinc; europium; biodiesel