Catalytic gasification of graphite by nickel in various gaseous environments

Controlled-atmosphere electron microscopy studies of the nickel/graphite system have revealed that in a strong oxidizing environment carbon gasification occurred mainly by the uncatalyzed route. Under the milder conditions of steam, catalyzed and uncatalyzed reactions occurred at comparable rates. In contrast, the reaction proceeded exclusively via catalyzed attack when experiments were performed in a hydrogen environment. However, in this case activity ceased at temperatures of around 1000 °C due to what is believed to be the formation of a strong nickel-carbon interaction resulting in the transformation of active metal particles, which formed a thin film along the edges of the catalytic channels they had produced at lower temperatures. Regeneration of particles could be achieved by heating in either oxygen at 850 °C or steam at 830 °C. The original activity pattern was restored if these specimens were subsequently heated in hydrogen. Although the precise cause and nature of the interaction between nickel and carbon is not fully understood, the results suggest a novel approach to redispersing large nickel particles.