Structural changes in a nickel-copper catalyst during growth of nitrogen-containing carbon nanofibers by ethylene/ammonia decomposition

Structural changes in a 65Ni-25Cu-Al₂O₃ catalyst during the decomposition of a C₂H₄/NH₃ mixture at different stages of nitrogen-containing carbon nanofiber (N-CNF) synthesis were studied by X-ray diffraction (XRD) analysis, X-ray diffraction using anomalous scattering effect and extended X-ray absorption fine structure (EXAFS) spectroscopy. The N-CNF growth over a catalyst particle was supposed to proceed via the formation of an oversaturated solid solution of carbon and nitrogen in a nickel-enriched alloy “NiCu_xC_yN_z”. The latter resulted in an increase of the alloy lattice parameter to abnormally large values а = 3.616-3.706 Å without destruction of its cubic structure. The formation of the “NiCu_xC_yN_z” phase and its presence in the system coincide with the optimum time for the synthesis of N-CNFs with the highest nitrogen concentration and maximum values of specific surface area and total pore volume.