Catalytic steam gasification of graphite: Effects of intercalated and externally added Ru, Rh, Pd and Pt

Abstract

The catalytic effect of platinum-group metals on the steam gasification of graphite was compared for two sets of samples. In one series the catalysts were introduced by impregnation from solutions, and in the other series they were intercalated between graphite basal planes. For a given metal, the specific gasification rates per unit of carbon-surface area were found to be similar in both instances. However, the catalytic activity differed very strongly. The difference in the gasification rate, measured at 850°C, was approximately one order of magnitude from one metal catalyst to the next, increasing in the order Pt, Pd, Ru, Rh. Changes in the intercalation structure during gasification were studied by X-ray diffraction. The morphology of the catalyst particles was followed by electron microscopy. Apparent activation energies were measured as a function of burn-off to distinguish between reaction regimes controlled by pore diffusion and by surface reaction. Frequently, the catalytic gasification was clearly impeded by pore diffusion, even after a large percentage of a sample had been gasified. An attempt was made to establish whether the catalytic action truly lowers the activation energy of carbon gasification, but a clear conclusion could not be reached.