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

Abstract

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 <i>n</i>-butanol/adipic acid was 3:1, and the ratio of the catalyst (the mass of magnetic solid acid) to liquids (the total volume of <i>n</i>-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 great potential for green chemical processes.