Synthesis, Structural Evolution and Catalytic Performance of Mg–Zr Perovskite and Perovskite‐Based Catalysts for Subcritical Ethanolysis of Omega‐3‐Depleted Microalgal Acid Oil

ABSTRACT A series of Mg–Zr perovskite and perovskite‐based catalysts with a fixed Mg:Zr molar ratio of 1:1 was synthesized via co‐precipitation and calcined at 500°C–1000°C for durations ranging from 0.5 to 4 h to investigate the relationship between structural evolution and catalytic performance. Comprehensive characterization (TG–DTA, XRD, BET, SEM) revealed a gradual transformation from low‐crystalline MgZrO 3 perovskite to dense MgO–ZrO 2 composites with increasing calcination temperature and time. Catalytic activity was first evaluated using refined coconut oil (total acid number, TAN < 0.1 mg KOH g −1 ) and palm fatty acid distillate (PFAD, TAN ≈ 170 mg KOH g −1 ) as model substrates. The ethyl ester selectivity increased from 89.1% for the ZM‐500‐2 h catalyst to 94.9% for the ZM‐1000‐2 h catalyst, while the final total acid number (TAN) of PFAD‐derived products decreased from 55 to 0.4 mg KOH g −1 , confirming that higher calcination temperature enhances catalytic robustness toward esterification. The optimal catalyst (ZM‐1000‐2 h) was further tested in the subcritical ethanolysis of omega‐3‐depleted microalgal acid‐oil (TAN ≈ 118 mg KOH g −1 ), achieving 97.1% total ethyl ester selectivity and a final TAN of 0.4 mg KOH g −1 . The superior activity is attributed to thermally stabilized acid–base interfacial domains within the ceramicized MgO–ZrO 2 composite, enabling simultaneous esterification and transesterification under subcritical ethanol (200°C, 4 MPa). The resulting biodiesel met international quality standards, confirming the practical potential of the process. Controlled perovskite‐to‐composite transformation in Mg–Zr systems thus yields robust, bifunctional catalysts for single‐step biodiesel production from high‐acid lipid residues.