Catalytic frontiers in biodiesel: Comparing bimetallic nano-catalysts and MOF-based catalysts for green energy – A review

Fossil fuels have detrimental environmental effects, such as global warming and climate change, prompting the search for alternatives. Biofuels, especially biodiesel, are good options. Biodiesel is usually made by the transesterification or esterification of plant-based resources (waste cooking oil, non-edible oil, edible oil, algae), with different catalysts. Many traditional homogeneous and heterogeneous catalysts exist, but soap formation, corrosion, low reusability, and mass transfer limitations hinder industrial application. Therefore, many recent research efforts are being made towards advanced catalytic systems that can avoid these issues. In this review, we present the use of bimetallic nano-catalysts (Ni–Co, Pd–Ag, Pt–Au) and metal–organic framework (MOF) catalysts (ZIF-8, UiO-66) in order to improve reaction selectivity and transform triglycerides into biodiesel. Bimetallic nano-catalysts are known to provide synergistic effects and reasonably good surface stability. MOF-based catalysts provide the benefits of large surface areas, porosity, and active sites for the reaction to occur under mild conditions. In general, compared to traditional catalysts, both bimetallic nano-catalysts and MOF-based catalysts have better activity, stability, and reusability. This review surveys their synthesis, catalytic mechanisms, and performance optimization. We also discuss key issues, such as catalytic deactivation, leaching, and scalability, along with future directions for research to support industrial scale-up.