Metal oxide-based heterogeneous acid catalysts for sustainable biodiesel synthesis: recent advances and key challenges.

The synthesis of biodiesel is given wide attention due to its environmental benefits, renewability, and long-term sustainability. Importantly, it can also contribute to the elimination of the current global energy and climate change challenges. However, its production has been studied by the diverse catalytic systems. Metal oxide-based heterogeneous acid catalysts exhibit superior properties such as excellent reactivity, high thermal stability, resistance to free fatty acids and water, and reusability. Hence, the development of highly efficient and stable metal oxide-based heterogeneous acid catalysts is essential for future industrial applications. This review systematically explores recent developments in the production of biodiesel using metal oxide-based heterogeneous acid catalysts. The catalyst design and preparation, structural and physicochemical properties, operating reaction conditions, and catalytic behaviors of metal oxide-based heterogeneous acid catalysts, including sulfated metal oxide catalysts, different metal oxide-based acid catalysts, mixed metal oxide-based acid catalysts, and MOF-derived metal oxide-based catalysts, are discussed. Finally, the review concludes with guidance on the rational design of metal oxide-based heterogeneous acid catalysts for eco-friendly and cost-effective biodiesel production and puts forward the current research challenges and future development perspectives, aiming to promote innovation in large-scale industrial biodiesel production.