Nickel antigorite synthesis and carbon tubular nanostructures formation on antigorite-based nickel particles by acetylene decomposition

We have synthesized nickel antigorite in order to obtain, by Subsequent heat treatment and reduction, supported nickel particles more or less anchored in the antigorite structure and rather well oriented depending on the temperature. The sample prepared at low temperature (450 degrees C) lead to mainly anchored Ni particles on rather well structured antigorite. For the samples prepared at intermediate temperatures (530, 600 degrees C) increasing destructuring of antigorite with temperature is observed. Finally, for the sample prepared at the highest temperature (700 degrees C) weakly bound Ni particles on a support resembling amorphous SiO2 are mainly obtained. Acetylene decomposition performed around 600 degrees C on these samples yield small amounts of carbon tubular nanostructures (nanotubes and nanofilaments). However, we have found that, whatever the temperature, carbon tubular nanostructures growth (tip growth mechanism) is favoured on the destructured regions of the material where the Ni particles are weakly bound to the suppconsequently observed for the higher temperature samples. We attributed this behaviour to the fact that the strongly bound anchored Ni particles mainly exhibitort. Higher density of tubular nanostructures is consequently observed for the higher temperature samples. We attributed this behaviour to the fact that the strongly bound anchored Ni particles mainly exhibit (1 1 1)-type faces, which are known to promote carbon precipitation. This would lead to coking when particles are not able to rearrange (as it is the case for the anchored particles) whereas carbon tubular nanostructures may grow on weakly bound particles that are able to rearrange. (c) 2005 Elsevier B.V. All rights reserved.