EFFECT OF SULFUR ON THE INTERACTION OF NICKEL WITH ETHYLENE

Although it is well known that sulfur acts as a poison for many nickel catalyzed reactions, it is now being recognized that certain benefits can be derived from following a partial and well controlled sulfidati on treatment of the metal. The current investigation was undertaken to ascertain the influence of sulfur on the formation of carbon filament s arising from the nickel catalyzed decomposition of ethylene/hydrogen mixtures. We have determined not only variations in the concentration s of the gaseous products, but also the amount and characteristics of the solid carbon deposit, as a function of several parameters. It is s uggested that the observed enhancement in carbon flament growth follow ing pre-treatment of nickel in low levels of H2S (4-50 ppm) is related to a reconstruction of the metal surface. The inhibition of catalytic activity resulting from a more severe pre-treatment in H2S is ascribe d to the formation of a 2-D or 3-D bulk sulfide. Pre-adsorption of sul fur on nickel induced some major perturbations in the morphological ch aracteristics of the filamentous carbon deposit, which are generated i n the form of regularly coiled structures. In contrast, those produced from unadulterated metal particles were found to be relatively straig ht. This change in growth mode indicates that sulfur is modifying the diffusion characteristics of carbon species through the catalyst parti cle.