XPS study of. beta. -carbon hydrogenation on Nickel(111) surface

The methanation reaction has been studied extensively using conventional catalysis and modern surface science techniques. It is now well established that the mechanism of this reaction involves the dissociative adsorption of carbon monoxide to produce highly reactive carbidic carbon (..cap alpha..-carbon) which is subsequently hydrogenated to produce methane. Under conditions of low hydrogen concentration, and high temperature, however, the reactive ..cap alpha..-C can be transformed into relatively less-reactive graphitic carbon (..beta..-carbon). The nature of ..beta..-carbon has been suggested to be graphitic as characterized by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and temperature programmed surface reaction (TPSR) in hydrogen. Using XPS, it is demonstrated directly that conversion of ..beta..-carbon to ..cap alpha..-carbon does occur at ..beta..-carbon hydrogenation temperature and that the rate-determining step in the hydrogenation of ..beta..-carbon may be the detachment of carbon atoms from ..beta..-carbon islands. 19 references, 6 figures.