Developments in Titanium-Based Alkali and Alkaline Earth Metal Oxide Catalysts for Sustainable Biodiesel Production: A Review.

Biodiesel represents a biodegradable, environmentally friendly, and renewable alternative to fossil fuels. Despite more than three decades of research, significant obstacles still hinder the widespread production of biodiesel. This current review elucidates both the potential and the existing challenges associated with homogeneous and heterogeneous catalysts in catalyzing biodiesel production, with a particular focus on alkali analogues, alkaline earth metal oxides, and titania-based catalysts. In particular, a comprehensive analysis is presented concerning alkali and alkaline earth-based titania (TiO 2 ) catalysts. Among these, the alkaline earth metal oxides, including lithium, calcium, and strontium when combined with titanium-based catalysts, exhibit superior catalytic activity compared to other metal oxides, owing to their heightened basicity. Consequently, this review offers a thorough and up-to-date insight into the potential of titania-based heterogeneous catalysts for advancing biodiesel production.