Fabrication of MIL-100(Fe)@SiO2@Fe3O4 core-shell microspheres as a magnetically recyclable solid acidic catalyst for the acetalization of benzaldehyde and glycol

Heterogeneous catalysts with convenient recyclability and reusability are vitally important to reduce the cost of catalysts as well as to avoid complex separation and recovery operations. In this regard, magnetic MIL-100 (Fe)@SiO2@Fe3O4 microspheres with a novel core-shell structure were fabricated by the in-situ self-assembly of a metal-organic MIL-100(Fe) framework around pre-synthesized magnetic SiO2@Fe3O4 particles under relatively mild and environmentally benign conditions. The catalytic activity of the MIL-100(Fe)@SiO2@Fe3O4 catalyst was tested for the liquid-phase acetalization of benzaldehyde and glycol. The MIL-100(Fe)@SiO2@Fe3O4 catalyst has a significant amount of accessible Lewis acid sites and therefore exhibited good acetalization catalytic activity. Moreover, due to its superparamagnetism properties, the heterogeneous MIL-100(Fe)@SiO2@Fe3O4 catalyst can be easily isolated from the reaction system within a few seconds by simply using an external magnet. The catalyst could then be reused at least eight times without significant loss in catalytic efficiency.