Hydrogenation kinetics of carbonaceous layers on polycrystalline iron

Carbonaceous layers were formed on iron by the $\text{CO}\text{H}{}_2$ reaction at 560 K and 1 bar total pressure. These layers were characterized by the C 1 s electron binding energy and peak area. Subsequently they were hydrogenated in 1 bar H₂ at 560 K to predominantly methane. There are two distinct stages of carbon hydrogenation: a fast initial stage where the rate depends sensitively on the total amount of deposited carbon, and a very slow second stage. The first stage corresponds to the removal of CH_x and carbidic carbon phases whereas the presence of graphitic carbon is indicated during the second stage. The initial rate of carbon hydrogenation is directly proportional to the rate of methane production from $\text{CO}\text{H}{}_2$ (at constant carbon coverage). From this behavior it was concluded that methane is formed by a direct hydrogenation of atomically adsorbed carbon.