| Due to widely applications of catalytic hydrogenation in the chemical industry,the development of catalysts and the study of reaction mechanism are of practical importance.Aromatic amine compounds are widely used as the intermediate for the manufacture of pharmaceuticals,fine chemicals,dyes,etc.,which makes selective hydrogenation of nitro aromatic compounds important in the catalytic industry.Recently,with the continuous development of new carbon materials,metal-free carbon-based catalysts gradually showed the advantages of low cost,friendly environment,high activity and high selectivity,which attracted many researchers’attention.Herein,a series of highly efficient and stable nitrogen-doped carbon nanotubes（N-doped CNTs）was synthesized and evaluated for the selective hydrogenation of various nitroarenes.Furthermore,the reaction mechanisms and kinetic behaviors of hydrogenation on the N-doped CNTs were initially explored.First,chitosan was used as the nitrogen source to modify carbon materials to synthesize a series of N-doped CNTs catalyst.Effects of preparation conditions were systematically investigated,and the optimum conditions were determined.Successfully doping of nitrogen into carbon skeleton with high degree of disorder were jointly proved by various characterization technologies.The as-prepared catalyst could only reduce nitro group,and the activity of the catalyst was negatively correlated with the electronegativity of the substituent on the aromatic rings.Also,the catalyst was a good candidate to prepare halogen-containing anilines,especially the product with iodo group,which benefited from the high relative contents of pyrrolic N and graphitic N.The as-prepared catalyst also exhibited excellent stability and recyclability in hydrogenation reaction.Next,the influences of reaction conditions on the initial reaction rate catalyzed by polypyrrole-doped CNTs were studied.Reaction solvent,amount of catalyst,reaction temperature and hydrogen pressure had significant influences on the activity of the catalyst,while the initial concentration of substrate under this condition had little effect on the initial reaction rate in this study.Combining the above results with quasi-steady state approximation,a hydrogenation mechanism was proposed.The rate-determining step was the activation of hydrogen on the catalyst.The kinetic analysis revealed that the reaction rate is a first-order dependence to H2 pressure and zero-order dependence to substrate concentration,which were consistent with the experimental data.Therefore,zero-order rate equation can be applied to fit the kinetic data under constant pressure of H2.The apparent activation energy of hydrogenation on the as-prepared catalyst was calculated to be 42.20 k J/mol.In addition,non-polar hydrogen radical was identified as the main form of active hydrogen species during hydrogenation.Finally,different polymers of polypyrrole was prepared and employed as the Nprecursor for the generation of N-doped carbon-based metal-free catalysts using various methods of calcination,pore formation and hard template.The hydrogenation activity of N-doped CNTs,prepared by using chitin or short peptide（WWW）as the nitrogen source,was investigated.The results showed that the structure of nitrogen precursor and its interaction with CNTs had a significant effect on the hydrogenation activity. |
