Synthesis of magnetically recyclable MOF-5@SiO2@Fe3O4 catalysts and their catalytic performance of Friedel–Crafts alkylation

Magnetic Fe3O4 particles were synthesized by solvo-thermal method, and then hydrolysis method was used to encapsulate a compact layer of SiO2 on the surface of Fe3O4 particles. Finally, the magnetic MOF-5@SiO2@Fe3O4 catalysts were prepared by in situ coating different contents of MOF-5 on the surface of SiO2@Fe3O4 particles. The as-synthesized samples were characterized by TEM, SEM, XRD, FT-IR, N2 adsorption/desorption, VSM and NH3-TPD. The catalytic activities of the magnetic MOF-5@SiO2@Fe3O4 catalysts for the Friedel–Crafts alkylation of toluene with benzyl chloride were evaluated. The results showed that magnetic MOF-5@SiO2@Fe3O4 catalysts exhibited superparamagnetic property, and could be separated by a magnet from the liquid reaction system. The conversion of toluene was increased gradually with the increase of catalyst contents and reaction temperature, respectively. 97 % conversion of toluene has been achieved by using 26.8 %MOF-5@SiO2@Fe3O4 catalyst at 120 °C for 6 h. Furthermore, electron-donating group, such as –OCH3, and –CH3, exhibited positive effect on the alkylation reaction. Besides, the catalyst could be easily separated from the reaction mixture after the reaction and reused for five times without significant decrease in activity.