Octyl and propylsulfonic acid co-fixed Fe3O4@SiO2 as a magnetically separable, highly active and reusable solid acid catalyst in water

Abstract

Modifications of propylsulfonic acid-fixed Fe3O4@SiO2 with three organosilanes (C2, C8, and phenyl) were investigated to develop a magnetically separable solid acid catalyst active for hydrolysis of ethyl acetate in excess water. Among the organosilanes, triethoxy(octyl)silane was the best modifier for improvement in catalytic activity, with activity of approximately twice that of the unmodified catalyst. The catalytic activity was comparable to those of Cs2.5H0.5PW12O40 and H3PW12O40 anchored on hydrophobic SBA-15 if compared per acid sites, though the acid strength of sulfonic acid was much weaker than that of H3PW12O40. High hydrophobicity over the surface and around the acid sites created by the octyl group was responsible for the high catalytic activity and the high stability in water. In addition to the improvement in catalytic activity, modification with the octyl group provided high stability for repeated uses of the catalyst in the reaction and there was little decrease in activity over at least four reuses. The catalyst was easily separated from the reaction solution by application of an external magnetic field.