Recent advances in magnetic solid catalysts: Synthesis, stabilization and application in cleaner production of biodiesel

Biodiesel is generally obtained by transesterification and esterification of appropriate feedstocks facilitated by a catalyst. It has emerged to be one of the most potential alternatives for the conventional fuels gaining worldwide attention. Heterogeneous catalysts are usually preferred than homogeneous for biodiesel synthesis due to facile separation and insignificant soap formation. However, the separation still possesses difficulty leading to mass transfer hindrance. Therefore, these catalysts can be further modified using magnetic separation techniques to develop magnetically separable catalysts. The magnetic nanoparticles (MNPs) are notable appealing catalysts due to huge surface area, high activity, amicable functional groups and structures, adaptable properties, conformity in pore size, and facile separation have made them desirable catalyst carriers for biodiesel synthesis. The MNPs are modified via functionalization to construct magnetically recoverable heterogeneous nanocatalysts. Magnetic catalysts can be utilized as a befitting option for biodiesel synthesis as these are environmentally benign, highly reusable and economically viable. The current review article discusses different magnetic solid catalysts such as magnetic base, acid, biocatalysts and bifunctional of acid base catalysts for efficient biodiesel synthesis. The prime focus of this paper rest on the catalytic performances of various magnetically recoverable catalysts, mechanisms and recyclability for biodiesel production processes. The synthesis methods of magnetic heterogeneous base and acid nanocatalysts, magnetic properties, functionalization and their reciprocity on the catalytic activity are reviewed in this article.