Mechanism of porous filamentous carbon granule formation on catalytic hydrocarbon decomposition

We have studied the growth of catalytic filamentary carbon granules formed on methane decomposition over Ni catalysts. As a result, a hundred-fold increase in the particle volume can be obtained. It was established that as Ni concentration in the initial catalyst increases, the solidity of catalytic filamentary carbon (CFC) aggregates, formed on methane decomposition, increases. In the course of CFC formation on the finely-disperse catalyst of high nickel content, the inner structure of the growing granule transforms from the dense agglomerate of nickel particles into a dense carbon filament packing with rather large single internal cavities (cracks). On the granule surface there is a layer whose filament packing remains loose. We propose the physical model of granule formation. (C) 1999 Elsevier Science Ltd. All rights reserved.