Nitrogen-containing carbon nanotubes (NCNTs) were prepared via pyrolysis of acetonitrile over cobalt catalysts at different temperatures to control the nitrogen content. The changes in the chemical and structural properties of undoped CNTs and NCNTs were investigated using high-resolution X-ray photoelectron and Raman spectroscopy. The NCNTs prepared at 550°C had a higher amount of pyridinic groups and edge plane exposure than the ones prepared at 750°C. The thermal stability and transformation of these nitrogen functional groups was studied using deconvoluted XP N 1s spectra. The NCNTs show a considerably higher activity in the oxygen reduction reaction in acidic electrolyte compared with undoped CNTs as demonstrated by cyclic voltammetry, rotating disk electrode measurements, and the redox-competition mode of scanning electrochemical microscopy (RC-SECM). Particularly, the NCNT sample prepared at 550°C exhibited the highest activity, which was about 1 order of magnitude lower than that of a commercial Pt/C sample containing 20 wt % Pt. The oxygen reduction reaction (ORR) performance of this sample showed hardly any signs of deterioration after 3 days, as determined by voltammetric stability tests in H 2 SO 4 .

Nitrogen-containing carbon nanotubes (NCNT) were grown from acetonitrile, pyridine or N,N-dimethylformamide over a supported Fe-, Co-or Ni catalyst in the temperature range 823-1123 K. The physico-chemical properties of the obtained NCNT, such as the C/N ratio or the nitrogen type, were related to the synthesis parameters. It was found that the C/N ratio increased with increasing temperature which could be related to the thermodynamic stabilities of the metal-carbides and metal nitrides. Also the type of nitrogen present in the graphene layer changed with increasing temperature from predominantly pyridinic-to quaternary nitrogen. NCNT obtained with the Fe catalyst showed bamboo morphology regardless of the C/N source or growth temperature while straight tubes were obtained with the Co-or Ni catalyst. We propose that this difference in morphology can be explained by the thermodynamic stabilities of the different metal-carbides, leading to a 'pulsating' growth in the case of Fe as opposed to a more continuous growth in the case of Co or Ni.

Nitrogen-containing carbon nanotubes (NCNT) are effective re-usable solid base catalysts, their activity for a Knoevenagel condensation being related to the amount of pyridinic nitrogen incorporated in the NCNT structure, which could be tuned by the synthesis parameters of the catalyst.