Novel Magnetically-Recoverable Solid Acid Catalysts with a Hydrophobic Layer in Protecting the Active Sites from Water Poisoning

Three novel magnetically-recoverable solid acid catalysts (hydrophobic catalysts Fe₃O₄@SiO₂-Me&PrSO₃H, Fe₃O₄@SiO₂-Oc&PrSO₃H and hydrophilic catalyst Fe₃O₄@SiO₂-PrSO₃H) were synthesized by introducing organic propylsulfonic acid and alkyl groups to Fe₃O₄@SiO₂ nanocomposites. We characterized these catalysts by FT-IR, EDS, XRD, VSM and SEM, and found that they had excellent core-shell structure and magnetic responsiveness. We also explored the impact of surface hydrophobicity on activity and stability of catalysts in ethyl acetate (EAC) synthesis reaction. The results indicated that: for reactivity and reusability, Fe₃O₄@SiO₂-Oc&PrSO₃H > Fe₃O₄@SiO₂-Me&PrSO₃H > Fe₃O₄@SiO₂-PrSO₃H. This was because octyl and methyl groups could build a hydrophobic layer on the surfaces of Fe₃O₄@SiO₂-Oc&PrSO₃H and Fe₃O₄@SiO₂-Me&PrSO₃H, and this could effectively prevent water molecules from poisoning active sites; the hydrophobicity of octyl was stronger than methyl. Fe₃O₄@SiO₂-Oc&PrSO₃H also showed higher catalytic activity in the external aqueous reaction system, which indicated that it had good water toleration. Moreover, we could easily separate Fe₃O₄@SiO₂-Oc&PrSO₃H from the reaction mixture with an external magnetic field, in the meanwhile, its reactivity could still remain above 80% after reusing 6 times.