Nitrogen-doped carbon confined cobalt nanoparticles as the steric acid-base multifunctional catalysts for Knoevenagel condensation

Nitrogen-doped carbon confined cobalt nanoparticles (Co-N-C) were synthesized through multi-step pyrolysis method. The Co-N-C samples exhibit excellent catalytic performance in the Knoevenagel reaction of benzaldehyde and malononitrile, of which the yield can be as high as 93.7% within 2.5 min with outstanding stability and recyclability. The catalytic performance may be primarily ascribed to the richness in nitrogen and cobalt in the form of the solid Frustrated Lewis Pair (FLP), i.e. the Co ion acts as a Lewis acid site to activate the carbonyl oxygen of benzaldehyde molecules, and nitrogen in carbon acts as a Lewis base site to activate the methylene hydrogen of malononitrile. From the perspective of intrinsic catalytic activity, variations in catalytic properties are attributed to the electron density distribution on the surface of the catalyst.