Preparation of magnetically recyclable MIL-53(Al)@SiO2@Fe3O4 catalysts and their catalytic performance for Friedel–Crafts acylation reaction

• Novel magnetically recyclable MIL-53(Al)@SiO2@Fe3O4 catalysts were prepared.
• The structure of the catalysts was characterized by XRD, TEM, SEM, FT-IR, and VSM.
• The magnetic catalyst had good activity for Friedel–Crafts acylation reaction.
• The catalyst can be easily separated from the reactant by an external magnet.
• The recovery catalyst can be reused for five times and showed excellent reusability.

Novel magnetically recyclable MIL-53(Al)@SiO2@Fe3O4 catalysts with different MIL-53(Al) contents were prepared by encapsulating magnetic SiO2@Fe3O4 nanoparticles into MIL-53(Al) through an in situ method. The structure of the catalysts was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, vibration sample magnetometer (VSM), and N2 adsorption/desorption techniques. Catalytic activity and recovery properties of the catalysts for Friedel–Crafts acylation reaction of 2-methylindole with benzoyl chloride were evaluated. The results showed that the magnetic MIL-53(Al)@SiO2@Fe3O4 catalysts have the larger surface areas, suitable superparamagnetism, and good catalytic activity for Friedel–Crafts acylation reaction. Over 38.8% MIL-53(Al)@SiO2@Fe3O4 catalyst under the reaction conditions of 25 °C for 8 h the conversion of 2-methylindole can reach ∼98%, and the selectivity of 3-acetylindole and that of N-acetylindole can reach ∼81% and ∼18%, respectively. After the reaction, the catalyst can be easily separated from the reactant mixture by an external magnet. The recovered catalyst can be reused for five times, and the conversion of 2-methylindole can be kept over 90% and the selectivity of 3-acetylindole can be maintained at 80%.

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