<![CDATA[This study investigates the production of biodiesel, specifically fatty acid methyl esters (FAME), derived from waste orange peel oil (OPO) via transesterification. A mixed metal oxide heterogeneous catalyst was synthesized using a coprecipitation method in the presence of soluble sodium carbonate and evaluated for the conversion of OPO with methanol. The physicochemical properties of the catalyst were characterized using X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and BET surface area analysis via N₂ adsorption-desorption at 77 K. Characterization results indicated that calcium oxide (CaO) particles formed and dispersed on the zinc oxide (ZnO) support, with higher ZnO content enhancing CaO dispersion. Under optimized transesterification conditions, the catalyst achieved a FAME yield of 73.04% at a CaO:ZnO ratio of 0.31 within 120 minutes. The resulting biodiesel exhibited a density of 0.872 g/cm³ and a refractive index of 1.451. These findings demonstrate the potential of this mixed metal oxide catalyst for biodiesel production and highlight the importance of optimizing reaction parameters to enhance both yield and fuel 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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