Synthesis of nitrogen-containing carbon nanofibers by catalytic decomposition of ethylene/ammonia mixture

The formation of carbon nanofibers (CNFs) doped with nitrogen was investigated during decomposition of C2H4/NH3 mixtures at 450–675 °C over metal catalysts: 90Ni–Al2O3, 82Ni–8Cu–Al2O3, 65Ni–25Cu–Al2O3, 45Ni–45Cu–Al2O3, 90Fe–Al2O3, 85Fe–5Co–Al2O3, 62Fe–8Co–Al2O3, 62Fe–8Ni–Al2O3. It was found that the yield of CNFs, their structural and textural properties, as well as nitrogen content in CNFs are strongly dependent on the synthesis conditions such as: catalyst used, feed composition, temperature and duration. The 65Ni–25Cu–Al2O3 was proved to be the most efficient catalyst for the production of nitrogen-containing carbon nanofibers (N-CNFs) with nitrogen content up to 7 wt.%. Ammonia concentration in the feed equal 75 vol.%, temperature 550 °C and duration 1 h were found to be the optimum reaction parameters to reach the maximum nitrogen content in N-CNFs. TEM studies revealed that the nanofibers have a helical morphology and a “herringbone” structure composed of graphite sheets. According to the XPS data, the nitrogen incorporation in the N-CNF structure leads to the formation of two types of nitrogen coordination: pyridinic and quaternary, and their abundance depends on the reaction conditions.