A strategy of two-step tandem catalysis towards direct N-alkylation of nitroarenes with ethanol via facile fabricated novel Co-based catalysts derived from coordination polymers

Abstract

Three novel N-doped carbon supported Co/Co3O4 catalysts, namely, Co@CN-hmta, Co@CN-larg and Co-Co3O4@CN-bipy, with sheet-, worm-, honeycomb-like morphologies respectively, have been fabricated by the pyrolysis of well-defined coordination polymers (CPs). Upon the as-prepared catalysts were applied for the reaction of N-alkylation of nitroarenes with ethanol, a direct two-step tandem reaction is realized, in which the Co@CN-hmta delivers 100% conversion/selectivity of N-ethylaniline/N,N-diethylaniline from the direct N-alkylation of nitroarenes with ethanol. The kinetic studies were conducted to confirm that the N-alkylation of aniline with ethanol is the rate-determining step in the two-step tandem reaction. The SEM/EDX, XRD, Raman, TEM, XPS, and CO2-TPD characterization results have revealed that sizes and dispersion of metallic Co, amount of structural defects and surface Lewis basicity towards three catalysts can be tuned by changing the structures of Co-based CPs designed by different organic linkers, which may also help to understand the preparation of industrial catalysts on a molecular level. The optimized Co@CN-hmta catalyst is easily recycled by using the external magnet for successive reuses without any loss in both activity and selectivity. To the best of our knowledge, this is the first carbon-nitrogen species supported Co/Co3O4 catalysts derived from the CPs, which could effectively catalyzed the N-alkylation of nitroarenes with ethanol to produce the secondary amines and/or tertiary amines. This low-cost, recyclable and easy scale-up N-doped carbon supported catalyst may be of potential application in various heterogeneous catalytic reactions.