Synthesis of a Y–Sr–Mg trimetallic oxide biochar-supported catalyst for transesterification toward sustainable biodiesel production

The development of sustainable and efficient heterogeneous catalysts is a major challenge in biodiesel production. In this study, a trimetallic oxide catalyst was synthesized for the transesterification reaction. The Y–Sr–Mg precursor solution was prepared at a 2:1:1 molar ratio; subsequently, a 1.5% (w/v) precursor solution was supported on biochar derived from Chlorogonium capillatum microalgae. Four catalysts, metal-loaded biochar catalyst (MLBC), metal-doped algal biomass (MDAB), nanoparticle-loaded biochar catalyst (NPBC), and nanoparticle-doped algal biomass (NPAB), were prepared using different synthesis methods for comparative analysis. Among all, MLBC showed superior physicochemical properties, with a well-developed mesoporous structure, and BET analyses revealed a maximum specific surface area of 32.20 m2/g. FESEM and TEM analyses revealed a porous, interconnected morphology with evenly distributed nanoparticles (20–50 nm) and low aggregation. XRD confirmed the formation of stable metal oxide phases without impurities, while FTIR showed the presence of both metal–oxygen bonds and biochar functional groups. EDS analysis validated successful trimetallic incorporation. MLBC outperformed the other catalysts in both characterization and biodiesel yield, achieving the highest biodiesel yields of 83.80% at 0.5 wt.% and 92.20% at 1.0 wt% catalyst loading under a 6:1 methanol-to-oil ratio at 60°C for 1–2 h, with 99.6% FAME purity confirmed by GC–FID analysis. These results show the effectiveness of C. capillatum-derived biochar as a support for trimetallic catalysts in sustainable biodiesel production under mild operating conditions.