CARBON-FILAMENT GROWTH ON PLATINUM CATALYSTS

A combination of experimental techniques including controlled atmosphere electron microscopy, thermogravimetry, and flow reactor studies have been used to study the formation of carbon deposits resulting from the interaction of platinum with ethylene and acetylene. It was found that in order to produce significant amounts of carbon on the metal it was necessary to perform the reaction in the presence of added hydrogen. In this investigation we have focused attention on all of the steps involved in the reaction, including those which occur at the metal-gas interface: diffusion of carbon through the metal particles and eventual precipitation at the metal-carbon interface to form a carbon filament. In both cases as the amount of hydrogen in the reactant gas was increased, there was a corresponding increase in the degree of crystalline perfection of the carbon filaments which were produced on the platinum particles. This effect was more pronounced for acetylene than ethylene, and if the metal was treated in a mixture of acetylene containing excess hydrogen, it was possible to produce filaments which had identical oxidation characteristics to those of graphite.