Synthesis of magnetically recyclable ZIF-8@SiO2@Fe3O4 catalysts and their catalytic performance for Knoevenagel reaction

•A series of novel magnetic ZIF-8@SiO2@Fe3O4 catalysts were synthesized.•The catalysts had the larger surface areas and the suitable superparamagnetism.•The catalysts exhibited good catalytic activity for the Knoevenagel reaction.•After reaction the catalyst can be easily separated by an external magnet.•The recovery catalyst can be reused five times and can keep its catalytic activity.

Novel magnetic ZIF-8@SiO2@Fe3O4 catalysts were synthesized by encapsulating magnetic SiO2@Fe3O4 nanoparticles into ZIF-8 through in situ method. The structures of the catalysts were characterized by TEM, SEM, XRD, FT-IR, VSM, N2 adsorption/desorption and CO2-TPD technology. The catalytic activity and recovery properties of the catalysts for the Knoevenagel reaction of p-chlorobenzaldehyde with malononitrile were evaluated. The results showed that the magnetic ZIF-8@SiO2@Fe3O4 catalysts had the larger surface areas, the suitable superparamagnetism, and good catalytic activity for Knoevenagel reaction. The conversion of p-chlorobenzaldehyde can reach ~98% and the selectivity of the production can reach ~99% over35.8%ZIF-8@SiO2@Fe3O4 (MZC-5) catalyst under the reaction condition of 25 °C and 4 h. The magnetic ZIF-8@SiO2@Fe3O4 catalysts also had good substrates adaptation. After reaction, the catalyst can be easily separated from the reaction mixture by an external magnet. The recovery catalyst can be reused five times and the conversion of p-chlorobenzaldehyde can be kept over 90%.

Graphical abstractNovel magnetically recyclable ZIF-8@SiO2@Fe3O4 catalysts were synthesized by encapsulating magnetic SiO2@Fe3O4 nanoparticles into ZIF-8 and the as-synthesized catalysts exhibited a good catalytic activity for the Knoevenagel reaction.Figure optionsDownload full-size imageDownload as PowerPoint slide