<![CDATA[Waste and biomass valorization provide promising routes for biofuel production while addressing environmental challenges associated with conventional feedstocks and energy-intensive processing. In this study, plant-mediated zirconia (ZrO₂) was hydrothermally prepared using Sapindus rarak extract (SPE) and evaluated as a catalyst for microwave-assisted hydroprocessing of used cooking oil (UCO) and Calophyllum inophyllum L. oil (CIO). Phenolic compounds and saponins were the predominant constituents of SPE, while the prepared ZrO₂ exhibited a predominantly tetragonal crystalline structure, nanoscale particles, and mesoporous characteristics associated with interparticle voids. Under microwave irradiation at 550 °C, with an H₂ flow rate of 20 mL min⁻¹, a catalyst-to-oil mass ratio of 1:100 (w/w), and a reaction time of 30 min, the prepared ZrO₂ promoted the formation of C₈–C₁₆ hydrocarbons with a higher paraffin fraction compared with commercial monoclinic ZrO₂ and catalyst-free treatment. Bio-jet fuel selectivity and yield reached 56.03% and 19.51 wt% for UCO and 48.90% and 15.72 wt% for CIO, respectively. Three consecutive reuse cycles with UCO resulted in a gradual decline in bio-jet fuel yield, accompanied by changes in product distribution and the retention of organic species on the catalyst. Altogether, these findings indicate the potential of plant-mediated ZrO₂ for microwave-assisted hydroprocessing of waste-derived and non-edible oils, while further catalyst development is needed to improve catalytic performance and product quality. Copyright © 2026 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).]]>
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