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

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 abstract: Novel 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. - Highlights: • 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