Bifunctional nanocatalysts for biodiesel production: Mechanisms, performance, kinetics, and future perspectives

چکیده مقاله

Bifunctional nanocatalysts have emerged as a promising class of materials for biodiesel production due to their ability to address key limitations associated with feedstock quality, reaction efficiency, and environmental sustainability. While numerous studies have reported the synthesis and application of such catalysts, existing reviews largely focus on either catalytic performance or material composition, with limited integration of reaction mechanisms, kinetic behavior, and structure-function relationships. To bridge this gap, the present review provides a comprehensive and critical assessment of bifunctional nanocatalysts designed with both acidic and basic active sites within a single nanostructure, enabling the simultaneous promotion of esterification and transesterification reactions. This dual functionality is particularly advantageous for processing low-cost, high free fatty acid (FFA) feedstocks, such as waste and non-edible oils, which are incompatible with conventional base catalysts due to soap formation. This review systematically discusses synthesis strategies, including sol-gel, co-precipitation, hydrothermal, and impregnation methods and elucidates how these approaches influence catalyst morphology, pore architecture, acid-base site distribution, and surface chemistry. A distinctive contribution of this work is the integrated analysis of catalytic mechanisms and reaction kinetics in relation to nanoscale structural features, offering insights into activity, selectivity, and stability trends. Furthermore, the recyclability, structural durability, and techno-environmental implications of bifunctional nanocatalysts are critically evaluated to assess their potential for scalable and sustainable biodiesel production. By correlating catalyst design principles with kinetic performance and future industrial perspectives, this review provides a unified framework to guide the rational development of next-generation bifunctional nanocatalysts aligned with circular economy and green energy objectives.