Different transfer hydrogenation pathways of halogenated nitrobenzenes catalyzed by Fe-, Co- or Ni-based species confined in nitrogen doped carbon

Abstract

In this work, by the simple pyrolysis of Fe2+, Co2+ or Ni2+ and 1,10-phenanthroline (Phen) complexes under the presence of activated carbon and dicyandiamide in nitrogen atmosphere, different nonprecious transition metal-based species that well confined in nitrogen doped carbon (M-N-C, M = Fe, Co or Ni) were prepared. The Fe-N-C showed the best catalytic performance for the transfer hydrogenation of halogenated nitrobenzenes. More importantly, through the catalytic results comparison of the three catalysts estimated by gas chromatography-mass spectrometer, two speculations might be presented for the reaction pathway depending on the catalyst used. The transfer hydrogenation reaction route over Fe-N-C might follow the indirect way like the Co-N-C and Ni-N-C. Another assumption was the Fe-N-C might go through the direct pathway in contrast to the Co-N-C and Ni-N-C which resulted in formation of azoxybenzene and azobenzene intermediates before complete conversion to aniline. Those differences were found to be correlated with the different valence states and active metal components in different catalysts. In addition, the optimal Fe-N-C could be efficiently recovered by using an applied magnetic field and reused without significant decrease of activity. Therefor the catalyst may possess important potential for the industrial application in the selective hydrogenation of halogenated nitrobenzenes.