Ionic liquids and deep eutectic solvents as catalysts for sustainable processes: applications in biodiesel production, <scp> CO ₂ </scp> conversion, and fuel desulfurization

Abstract Achieving a clean atmosphere requires the implementation of environmentally sustainable strategies to mitigate the detrimental effects of fossil fuels, which are associated with high sulfur content, substantial greenhouse gas emissions, and limited reserves. Biodiesel, with its low sulfur content, represents a promising and sustainable alternative. Ionic liquids are green catalysts that align with the principles of sustainability and green chemistry, and are used increasingly in biodiesel production. The conversion of CO 2 – a major contributor to global warming – into value‐added products offers a viable strategy to mitigate climate change. However, comprehensive reviews addressing the use of ionic liquids as catalysts in biodiesel production and their application in the conversion of CO 2 and sulfur compounds into valuable chemicals are lacking. This review provides an in‐depth analysis of recent advances in biodiesel production using ionic liquid‐based catalysts, including magnetic, enzymatic, and photocatalytic systems, with a focus on modifications to their acidic and basic properties. Notably, polyoxometalate‐based ionic liquids have demonstrated complete sulfur removal from diesel. The review also explores the utility of CO 2 ‐derived products in sustainable biodiesel production and evaluates the roles of ionic liquids and deep eutectic solvents as green solvents and catalysts. Greener synthesis pathways for these catalysts and their potential for commercialization are evaluated through techno‐economic assessments.