Advancements in Heterogeneous Biobased and Bio-Composite Catalysts: A Comprehensive Review on Synthesis, Characterizations, and Applications in Biodiesel Production

The synthesis of biodiesel from inedible feedstocks using bio-composite heterogeneous catalysts has emerged as a sustainable strategy to address global warming, enhance energy security, and preserve biodiversity. This review highlights advancements in eco-friendly catalysts derived from waste biomass, including eggshells, banana peels, agricultural residues (such as cocoa pod husks and sugarcane bagasse), and industrial by-products. These catalysts, which include CaO-based composites (such as Zn-doped CaO and Zr/CaO), sulfonated carbon materials, silica-impregnated CaO, and metal oxide-supported systems (such as ZrO₂/bamboo leaf ash and Cu/TiO₂), are designed to improve catalytic efficiency, reusability, and sustainability. Characterization techniques such as FTIR, XRD, SEM, XPS, and TGA confirm their structural stability, active sites, and thermal resilience, all of which are critical for optimizing biodiesel yield. The use of waste-derived catalysts not only reduces reliance on edible feedstocks but also promotes circular economy principles by valorizing biowaste. This review discusses challenges related to scalability, long-term stability, and cost-effective synthesis, as well as opportunities to refine catalyst design through advanced functionalization and hybrid systems. By merging sustainable chemistry with industrial applications, bio-composite catalysts offer a pathway to decarbonize energy systems, support local economies in developing regions, and align with global sustainability goals. The review emphasizes the need for interdisciplinary innovation to unlock the full potential of waste-derived catalysts in achieving a low-carbon future.