Preparation and performance of 3-APTMS-modified NiO/γ-Al₂O₃ for high-efficiency biodiesel production from used palm oil

Abstract

This study was done to determine performance of a dual-basic-site catalyst for biodiesel production, created by NiO impregnation on γ-Al₂O₃ and 3-APTMS grafting, enhancing reactant adsorption and catalytic efficiency. The catalyst was synthesized by first preparing NiO/γ-Al₂O₃ via dry impregnation of nickel onto a γ-Al₂O₃ support, followed by grafting with 3-aminopropyltrimethoxysilane (3-APTMS) to form NiO/γ-Al₂O₃-NH₂. The dual functionality, arising from the incorporation of NiO and amino groups, is designed to enhance reactant adsorption and improve catalytic efficiency. This innovative design addresses limitations of conventional catalysts by improving the interaction between active sites and reactants.The catalyst was initially evaluated for basicity using titration and characterized by FTIR and XRD, confirming the formation of NiO rather than Ni(OH)₂. The sample with the highest basicity was further analyzed using surface area analysis and SEM-EDX to determine its textural properties and elemental composition. The mesoporous, amorphous NiO/γ-Al₂O₃-NH₂ exhibited a surface area of 91.68 m²/g, a pore volume of 0.16 cm³ /g, and an average pore diameter of 3.03 nm. Transesterification reactions were performed under varying conditions, including temperatures of 55, 65, and 75 °C, reaction times of 1, 3, and 5 hours, catalyst loadings of 1, 3, and 5 wt%, and oil-to-methanol molar ratios of 1:6, 1:9, and 1:12. Under optimal conditions (55 °C, 1 hour, 1 wt% catalyst, 1:9 ratio), the biodiesel yield reached 83.15 % with 99.76 % methyl ester selectivity. The catalyst maintained its activity after three reuse cycles, underscoring the advantage of its dual basic site design and enhanced stability for biodiesel production.