Preparation and characterization of hydrotalcite-like compounds containing transition metal as a solid base catalyst for the transesterification

Hydrotalcite-like compounds (HTLCs) containing Mg2+, Fe3+ and Al3+ layered double hydroxide (LDH) were synthesized by co-precipitation method and calcined at 873 K for 16 h. These heterogeneous base catalysts were used for the transesterification of soybean oil with methanol to produce biodiesel. The Mg/Fe molar ratio was varied from 6 to 15, but the MgAlFe catalysts have a constant Al composition in the hydrotalcite-like structures. The catalysts were characterized by nitrogen physisorption, X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), CO2 temperature programmed desorption (CO2-TPD), field-emission scanning electron microscope (FE-SEM), and Fourier transfer infrared spectroscopy (FTIR). The conversion of fatty acid methyl ester (FAME) has been affected by the basicity and Mg content in the MgAlFe catalysts. When MgAlFe 15 was used, the highest basicity and high conversion of FAME (81%) was obtained due to the formation of Mg2+–O2−, Al3+–O2− pairs, and the higher CO2-desorption temperature.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (123 K)Download as PowerPoint slideHighlights► The Mg/Fe ratio was varied from 6 to 15 in the hydrotalcite structure. ► The highest conversion of FAME (81%) was obtained after 4 h reaction time when the Mg/Fe ratio is 15 and 0.3% catalyst was used. ► The conversion was affected by the basicity and Mg content, and the MgAlFe 15 showing the highest basicity among the catalysts.