Advances in Catalysts for Biodiesel Production: A Systematic Review of Trends, Challenges, and Future Prospects

Biodiesel has attracted worldwide interest as an alternative renewable fuel source to fossil fuels, but its industrial applications are limited to catalytic inefficiencies, high costs of production, and environmental trade-offs. This review summarizes the gains in catalyst development and process integration and aims to determine new trends, compare performance of different classes of catalysts, and provide a roadmap to sustainable adoption in industry. Scopus, Web of Science, and ScienceDirect were utilized to conduct a systematic review of peer-reviewed studies published between 2015 and 2025, covering both the historical milestones and the latest innovations. It is found that there is a strong transition between traditional homogeneous and heterogeneous heterogeneous systems and sophisticated nanocatalysts, bifunctional systems, MOFs, COFs, and biochar systems, which present varying benefits to activity, selectivity, and recyclability but remain at a disadvantage due to deactivation, feedstock effects, and bottlenecks in mass transfer. Ultrasound-assisted systems and microreactors have also facilitated intensifying reactions, whereas artificial intelligence (AI) and machine learning (ML) have made it possible to predictatively model catalyst performance, feedstock oscillations, and yield optimization. Regardless of these developments, high feedstock prices, techno-economic uncertainties, and life-cycle environmental issues still present a critical obstacle. In the future, the integration of hybrid catalysts, circular biorefinery, digital approaches, and facilitating policy frameworks will prove pivotal towards scaling the biodiesel production. Together, these avenues will make biodiesel not just a renewable transportation resource but also a key pillar of the circular bioeconomy and the global energy transition towards low-carbon.