Functional Nanomaterials-Catalyzed Production of Biodiesel

Background: Biodiesel, as a green and renewable biofuel, has great potential to replace fossil diesel. The development of efficient and stable heterogeneous catalysts is vital to produce biodiesel in an efficient and green way. Nanocatalysts provide a high surface-to-volume ratio as well as high active site loading and can improve mass transfer, which is beneficial to enhance their catalytic activity. Objective: The review focuses on the latest advances in the production of biodiesel using nanostructured catalysts. Methods: Biodiesel is mainly produced through esterification and transesterification reaction using acids, bases or lipases as catalysts. We mainly review the synthesis methods and physicochemical properties of various basic, acidic and lipase nanocatalysts. Meanwhile, their catalytic activities in biodiesel production are also discussed. Results: Alkali nanocatalysts are mainly suitable for transformation of oils with low acid values to biodiesel via transesterification reaction. In contrast, acidic nanocatalysts are not sensitive to water as well as free fatty acids and can avoid saponification associated with basic nanocatalysts while promote simultaneous esterification and transesterification reaction. However, acid-catalyzed transesterification usually requires harsh reaction conditions. In addition, the lipase-catalyzed process is also suitable for non-edible oils containing high contents of free fatty acids, which possess environmental and economic advantages. Conclusion: Nanocatalysts have many advantages such as good accessibility with nanostructure, high active site loading and reduction of mass transfer resistance. However, most of those materials undergo deactivation after several cycles. Therefore, the development of more efficient, stable, and low-cost nanocatalysts is desirable for producing biodiesel.