Preparation and Characterization of Sulfonated Magnetic SiO2 Microspheres as the Solid Acid Catalysts for Esterification

The sulfonated magnetic SiO2 microsphere solid acid catalysts were prepared by the impregnation and grafting methods with iron oxide magnetic nanoparticles (Fe3O4 MNPs) as the magnetic cores. The catalytic properties of the magnetic SiO2 solid acid catalyst were studied in detail. The characterization results showed that the SiO2 was successfully coated on the Fe3O4 MNPs. Compared with the grafting method, impregnated solid acid exhibits higher catalytic performance, which reached an esterification rate of up to 99.00% when the reaction temperature was 105 °C, the molar ratio of n-butanol/adipic acid was 3:1, and the ratio of the catalyst (the mass of magnetic solid acid) to liquids (the total volume of n-butanol and adipic acid) was 2.95%. The magnetic solid acid exhibited great separation ability and reusability. After six times of recycle, the conversion of the grafted magnetic solid acid still attained 85.61% compared with that of the impregnated magnetic solid acid, which reduced to 81.35%, holding g...