Homogeneous borotungstic acid and heterogeneous micellar borotungstic acid catalysts for biodiesel production by esterification of free fatty acid

•First example to efficiently catalyzed by H5BW12O40 attributing to its high acidity.•First assembly of micellar nanocatalyst (C16TA)H4BW12O40 had amphiphilic components.•Water-tolerant property available for esterification reaction.•The retrieved HPAs could be repeated without appreciable losing high performance.

A highly negatively charged borotungstic acid H5BW12O40 had been tested as homogeneous catalyst in esterification. Compared with common used H3PW12O40, it displayed a higher conversion (98.7%) and excellent efficiency (96.2%) due to its high amount of protons in methanol. In order to overcome the drawbacks of homogeneous heteropolyacid H5BW12O40, a Brønsted-surfactant-combined (C16TA)H4BW12O40 (C16TA = cetyltrimethyl ammonium) had been fabricated with strong acidity and nano-size micellar structure resulting in enhanced activity and stability during the reaction, which exhibited consistent activity during recycling in esterification reaction.

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