Silica-immobilized Aquivion PFSA superacid: application to heterogeneous direct etherification of glycerol with n-butanol†
We report the effective heterogenization of polymeric perfluorosulfonic acid (PFSA) Aquivion® resin in a silica network for the direct etherification of glycerol with aliphatic n-butanol. The Aquivion-silica composites, prepared by a template-free sol–gel method, presented a large specific surface area, affording highly accessible acid sulfonic groups. The textural and bulk/surface properties of the hybrid composites were characterized in-depth using TGA, acid–base titration, N2 adsorption–desorption, XRD, TEM, FTIR, Raman, CP-MAS NMR and XPS. The Aquivion-silica composites exhibited a high catalytic activity (91% n-butanol conversion) and selectivity (45% butyl glyceryl monoether yield) while they lowered the formation of by-product (6% dibutyl ether yield) as compared to benchmark homogeneous and heterogeneous acid catalysts. The catalyst was reusable and maintained a stable performance after six consecutive cycles.