Magnetic and Stable H3PW12O40-Based Core@shell Nanomaterial towards the Esterification of Oleic Acid with Methanol

Graphical A novel, magnetically recoverable, and stable catalyst, Fe 3 O 4 @SiO 2 –NH 2 /HPW@CS/HPW, has been prepared and a high methyl oleate yield of 93.2 % was achieved in the esterification of methanol and oleic acid. A magnetically retrievable and stable composite, Fe 3 O 4 @SiO 2 –NH 2 /HPW@CS/HPW, in which H 3 PW 12 O 40 (abbreviated as HPW hereafter) was successfully anchored onto the surface of a cross-linked chitosan coating on magnetic Fe 3 O 4 cores, has been prepared by means of chemical bonding between the amino and HPW components. The resultant composites were characterized by different physicochemical techniques, such as TEM, SEM, FTIR, and vibrating sample magnetometry (VSM). An improved synthesis of methyl oleate from oleic acid and methanol was observed with the as-prepared material as catalyst with easy recovery by simply using an external magnet. A yield of 93.2 % of methyl oleate was achieved under the optimal reaction conditions, that is, a 20:1 molar ratio of methanol to oleic acid and 0.4 g catalyst at 60 °C for 4 h. It was demonstrated that improved catalytic performance and facilitated separation were simultaneously achieved in the esterification reactions as a result of the core@shell structures in which stabilized HPW and magnetic cores are integrated into one body.