Magnetically-separable acid-resistant CoFeO@Polymer@MIL-100 core-shell catalysts for the acetalization of benzaldehyde and methanol.

Novel reusable acid-resistant magnetic polymer nanospheres-immobilized MIL-100 (CoFeO@Polymer@MIL-100) catalyst was prepared by a layer-by-layer method to achieve a controllable structure. The obtained core-shell catalyst consisted of modified magnetic nanoparticles as the core, a carboxylic-functionalized polymer as the protective layer, and an MIL-100 shell as the active catalytic layer by chemical bonds on the polymer. The catalysts showed good stability, good magnetic saturation, and acid corrosion resistance. The thickness of the MIL-100 shell could be adjusted by controlling the metal salt concentration and the number of layer-by-layer cycles. Nano-sized MIL-100 showed better mass transfer efficiency and catalytic activity. A conversion of 97.7% after 10 min was observed during acetalization when using CoFeO@Polymer@MIL-100 as the catalyst. CoFeO@Polymer@MIL-100 could be reused at least five times. The use of a polymer layer on CoFeO@Polymer@MIL-100 prevented acidic ligands from corroding the magnetic core. Chemical bonds between MIL-100 and functional magnetic polymer cores improved the catalyst's stability. CoFeO@Polymer@MIL-100 exhibited high activity, excellent stability, and easy magnetic separation.