Catalytic growth of carbon fibers from methane on a nickel-alumina composite catalyst prepared from Feitknecht compound precursor

Abstract

A nickel-alumina catalyst prepared from Feitknecht compound was used in the catalytic growth of carbon fibers from methane. An in situ thermal balance was employed in the study of the reaction and in the TPR of the oxide precursors. A number of catalysts from the same structure with different nickel to aluminum ratios were tested, for comparison with a nickel oxide also prepared by precipitation. All the samples containing aluminum exhibited high activity at a low temperature, yet the nickel oxide had no activity under the same conditions. It has been observed that, as the Ni/Al ratio increases, the crystallinity of the Feitknecht compound decreases. However, the amount of the carbon fiber formed before the deactivation of the catalyst is proportional to the amount of the nickel in the catalyst. The reduction and the reaction temperatures both have strong effects on the reaction. A small amount of hydrogen in the feed retards fibers formation. At 773 K, the weight of carbon fiber formed on one of the catalysts attained 85 times that of the original unreduced catalyst in the cofeeding of methane and nitrogen. SEM and TEM photographs showed that the carbon fibers formed winding tubes, and their diameters were in the range of 15–69 nm. The shape of the break sections and the existence of dislocations in the fibers suggest that the fibers formed in this work are in accord with the fishbone structure model.