Synthesis and Evaluation of Hydrotalcite Supported on Ordered Mesoporous Silica for Application in Biodiesel Production

Abstract The growing demand for renewable energy sources has driven the development of sustainable processes for biodiesel production, highlighting the use of heterogeneous catalysts as an alternative to conventional homogeneous systems. In this context, this study aimed to synthesize, characterize, and evaluate the catalytic performance of pure Mg/Al hydrotalcites and those supported on ordered mesoporous silica, investigating the influence of the Mg/Al molar ratio and the support structure on the catalytic performance in the transesterification reaction of soybean oil. However, it provides a systematic structure–property–performance correlation, highlighting the combined influence of Mg/Al ratio and mesoporous support on catalytic behavior, which remains insufficiently explored in the literature. The catalysts were synthesized by coprecipitation, varying the Mg/Al molar ratio (0.20, 0.25, and 0.33), and subsequently calcined at 550 °C to obtain the mixed oxides. Ordered mesoporous silica (SBA-15) was prepared by the sol-gel method and used as a support for the incorporation of the Mg/Al active phase. The materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption (BET), scanning electron microscopy (SEM), and programmed CO₂ desorption (TPD-CO₂), aiming to correlate structural, textural, and acid-base properties with catalytic activity. Catalytic evaluation was performed in the transesterification of soybean oil with methanol, under an oil: methanol molar ratio of 1:20, a temperature of 70 °C, and a reaction time of 5 h, with biodiesel analysis by gas chromatography. S-HT-Mg type catalysts exhibited high catalytic activity, with conversions ranging from 82 to 94%, attributed to a higher density of basic sites. Hydrotalcite catalysts supported on ordered mesoporous silica, on the other hand, exhibited lower conversions (37–50%), indicating that the support influences the accessibility of the active sites. The results confirm the potential of Mg/Al hydrotalcites as promising heterogeneous catalysts for the sustainable production of biodiesel.