A study has been made of the properties of the radicals formed by the dissociative adsorption of small volumes of methane,
n
-pentane, 2,2-dimethylbutane,
cyclo
hexane,
cyclo
hexene and benzene on a high area supported nickel cracking catalyst. Measurements have been made of (i) the change in volume of hydrogen adsorbed, after standard preparation of the catalyst, when a known volume of each hydrocarbon had been adsorbed; (ii) the products desorbed when adsorbed hydrocarbons were heated and (iii) the kinetics of removal of the hydrocarbon from the surface in a flow of hydrogen using a gas chromatographic analytical technique to investigate the products. Results showed that all the hydrocarbons were very strongly bonded to the surface and there was evidence that
n
-pentane, 2,2-dimethylbutane and
cyclo
hexane were rapidly dissociated on heating to form the same surface species as formed by the dissociative adsorption of methane, but the surface radicals formed on the adsorption of
cyclo
hexene and of benzene were somewhat different. All hydrocarbons desorbed a very considerable fraction of their constituent hydrogen on heating
in vacuo
. Quantitative removal of carbon on reaction of surface radicals with excess hydrogen yielded methane as the almost exclusive product by a second-order reaction in which the rate was directly proportional to hydrogen pressure and amount of carbon remaining on the catalyst. Rate constants for methane formation from adsorbed species of the saturated hydrocarbons (including adsorbed methane) were equal but differed in magnitude from those found for the unsaturated compounds, though the same kinetic laws were obeyed. A reaction mechanism is proposed which accounts for these observations.