Hydrotalcite-like compounds containing transition metals as solid base catalysts for transesterification

Hydrotalcite-like compounds (HTLCs) containing Mg2+, Ni2+ and Al3+ layered double hydroxide (LDH) were synthesized by co-precipitation method and calcined at 773 K for 10 h performed as heterogeneous base catalysts for transesterification of soybean oil with methanol to produce biodiesel. These four different MgAlNi catalysts were characterized by nitrogen physisorption, X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), temperature programmed desorption with CO2 (CO2-TPD), nitrogen adsorption–desorption. The Mg/Ni molar ratio varies over the range from 4 to 16 of the MgAlNi catalysts at a constant Al ratio in the hydrotalcite-like structures. The conversion of FAME was related to the basicity and Mg content of the MgAlNi catalysts, with MgAlNi 16 showing the highest basicity, and the lowest surface area due to Mg2+–O2− and Al3+–O2− pairs. The optimum conditions were obtained with a methanol/oil molar ratio of 21, 0.3% catalyst (w/w, oil), and 1200 rpm stirring speed for 4 h at 338 K, which results in the highest FAME conversion of 87%.

Graphical abstractThe conversion of FAME increases with increasing with methanol to oil molar ratio, and reach 21 to maximum, the activity of the MgAlNi catalysts in the following order: MgAlNi 16 > MgAlNi 12 > MgAlNi 8 > MgAlNi 4.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Mg/Ni molar ratio from 4 to 16 of MgAlNi catalysts in hydrotalcite-like structure. ► Mg/Ni molar ratio of 16, 0.3% catalyst shows a conversion of FAME of 87% for 4 h. ► Conversion of FAME was related to the basicity and Mg content of MgAlNi catalysts.