Effect of Cu on Performance of Self-Dispersing Ni-Catalyst in Production of Carbon Nanofibers from Ethylene

The development of effective catalysts for the pyrolysis of light hydrocarbons with the production of carbon nanomaterials represents a relevant direction. In the present work, the influence of copper addition on performance of a self-dispersed Ni-catalyst and structural features of the obtained carbon nanofibers (CNFs) was studied. The precursors of Ni and Ni-Cu catalysts were prepared by activation of metal powders in a planetary mill. During contact with the C2H4/H-2 reaction mixture, a rapid disintegration of the catalysts with the formation of active particles catalyzing the growth of CNFs has occurred. The kinetics of CNF accumulation during ethylene decomposition on Ni- and Ni-Cu catalysts was studied. The effect of temperature on catalytic performance was explored and it was shown that introduction of copper promotes 1.5-2-fold increase in CNFs yield in the range of 525-600 degrees C; the maximum CNFs yield (100 g/gcat and above, for 30-min reaction) is reached on Ni-Cu-catalyst at 575-600 degrees C. A comparative analysis of the morphology and structure of CNF was carried out using electron microscopy methods. The growth mechanism of carbon filaments in the shape of "railway crossties" on large nickel crystals (d > 250 nm) was proposed. It was found that the addition of copper leads to a decrease in the bulk density of the carbon product from 40-60 to 25-30 g/L (at T = 550-600 degrees C). According to the low-temperature nitrogen adsorption data, specific surface area (SSA) of CNF samples (at T < 600 degrees C) lies in the range of 110-140 m(2)/g, regardless of the catalyst composition; at T = 600 degrees C the introduction of copper contributed to an increase in the specific surface of CNF by 100 m(2)/g.