Modification of mesoporous zirconia using phosphoric acid and calcium oxide as a bifunctional nano-catalyst for one-pot conversion of used palm cooking oil into biodiesel

This study successfully synthesized a novel bifunctional nano-catalyst, phosphated mesoporous zirconia impregnated with calcium oxide (CaO/PO₄–MZ), and applied it for the conversion of used palm cooking oil, which had a free fatty acid (FFA) content of 2.65 % m/v, into biodiesel. The resulting CaO/PO₄–MZ nano-catalyst exhibited a total acidity of 1.93 mmol/g, a total basicity of 0.38 mmol/g, a specific surface area of 7.867 m²/g, a total pore volume of 0.035 cm³ /g, and an average pore diameter of 3.621 nm. Under optimized reaction conditions (reaction time = 3 h, catalyst dosage = 4 wt%, and methanol-to-oil molar ratio = 21:1), the nano-catalyst achieved a biodiesel yield of 86.49 % with a selectivity of 97.48 %. It outperformed mesoporous zirconia (MZ), phosphated mesoporous zirconia (PO₄–MZ), calcium oxide-impregnated mesoporous zirconia (CaO/MZ), and a sequential two-pot system using PO₄–MZ followed by CaO/MZ. Additionally, the nano-catalyst demonstrated good reusability, maintaining a 61.28 % yield after five cycles. Optimization using response surface methodology (RSM) with a central composite design (CCD) predicted an optimum biodiesel yield of 86.53 % under a reaction time of 3.17 h, a catalyst dosage of 4.04 wt%, and a methanol-to-oil molar ratio of 20.53:1, with an R² value of 0.9992. These findings highlight the potential of one-pot biodiesel production from used palm cooking oil as an efficient and environmentally friendly route for sustainable biofuel technologies. • A bifunctional CaO/PO₄–MZ nano-catalyst was developed for one-pot biodiesel synthesis. • Acid–base duality in CaO/PO₄–MZ improved efficiency over two-pot conversion. • Maximum biodiesel yield of 86.49 % and 97.48 % selectivity was achieved. • RSM–CCD optimization was applied to evaluate key reaction parameters. • Catalyst retained 61.28 % yield after five runs, confirming good reusability.