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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