Synthesis, characterization, and activity in transesterification of mesoporous Mg-Al mixed-metal oxides

In this work, a series of Mg-Al mixed-metal oxides with Mg/Al ratios of 0.125-8 were synthesized via a sol-gel method using cetyltrimethylammonium bromide as a template. All oxide samples were characterized by XRD, XRF, IR, DTA-TGA, TEM, and N₂ adsorption-desorption measurements. The phases of the Mg-Al mixed-metal oxides are the mixture of γ-Al₂O₃ and periclase (MgO) or the mixture of hydrotalcite (Mg₆Al₂CO₃(OH)₁₆·4H₂O) and periclase depending on the Mg/Al ratio. The Mg-Al oxides have mesoporous structure with surface areas in the range of 120-270 m²/g. These oxides were also impregnated with KI to increase their base strength, and their activities for biodiesel production were tested via the transesterification of soybean oil with methanol. The KI impregnated Mg-Al mixed-metal oxide at Mg/Al ratio of 4:1 has base strength in the range of 9.8 ≤ pK_BH⁺ ≤ 15 and, of all the catalysts tested, it is the most efficient catalyst for transesterification of soybean oil with methanol (>90% conversion after 8 h).