Methane selectivity of hydrogenolysis reactions on nickel

Hydrogenolysis of straight-chain pentane and octane was investigated on different nickel catalysts. A pure primary cracking is difficult to observe, because the whole process is a continuous multicracking on the surface of the catalyst. This seems to be a primary process without desorption and readsorption, a hypothesis verified by the very small effect of the space velocity on the selectivities (readsorption of a primary product and its further cracking would have given a strongly retention time-dependent selectivity pattern). The aim was to determine the effect of temperature on the multicracking process and the change of selectivities with temperature and with the liquid hourly space velocity (LHSV). Hydrogenolysis was the only reaction observed. Methane selectivity increased with temperature increase, whereas the selectivities for other hydrocarbons decreased. Methane was mainly produced by primary multicracking. Catalyst carrier had no effect on methane selectivity. It is suggested that the multicracking of a hydrocarbon is mainly primary and not a combination of primary and secondary processes.