Alkali and Alkaline Earth Metal Oxide-Modified Aluminosilicate and Zeolitic Ceramic Catalysts for Sustainable...

The development of efficient and sustainable ceramic catalysts for biodiesel production has attracted considerable attention as a strategy to reduce fossil fuel dependence and environmental impacts. This review critically examines alkali- and alkaline earth metal oxide-modified silicate, aluminosilicate, and zeolitic ceramic materials as heterogeneous catalysts for transesterification and esterification of lipid feedstocks. Emphasis is placed on the relationships between catalyst structure, surface acidity/basicity, and catalytic performance. Incorporation of alkali (K⁺, Na⁺, Li⁺) and alkaline earth (Ca²⁺, Mg²⁺) metal ions into ceramic frameworks enhances active-site density, reactant adsorption, and reaction kinetics, enabling biodiesel yields exceeding 90%-99% under optimized conditions. The effects of framework topology, pore architecture, and surface area on mass transfer and catalyst accessibility are discussed, together with the roles of zeolites, clays, and mesoporous aluminosilicates in improving catalyst stability, reusability, and resistance to leaching. Current challenges, including catalyst deactivation, feedstock impurities, and scale-up limitations, are critically evaluated. Emerging strategies involving waste-derived ceramics, bifunctional catalysts, and process intensification are highlighted to guide the rational design of next-generation heterogeneous catalysts for sustainable biodiesel production.