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

Novel magnetic ZIF-8@SiO 2 @Fe 3 O 4 catalysts were synthesized by encapsulating magnetic SiO 2 @Fe 3 O 4 nanoparticles into ZIF-8 through in situ method . The structures of the catalysts were characterized by TEM , SEM, XRD , FT-IR, VSM , N 2 adsorption/desorption and CO 2 -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@SiO 2 @Fe 3 O 4 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@SiO 2 @Fe 3 O 4 (MZC-5) catalyst under the reaction condition of 25 °C and 4 h. The magnetic ZIF-8@SiO 2 @Fe 3 O 4 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%.