Hydrogenolysis of saturated hydrocarbons on a nickel catalyst: II. Selectivity of hydrogenolytic cleavage of some aliphatic and alicyclic hydrocarbons and their reactivity

Abstract

The hydrogenolysis of octane, decane, isooctane, neohexane, and some alicyclic hydrocarbons, like alkylcyclopentanes, alkylcycloheptanes, and dialkylcyclohexanes, in the gaseous phase on a nickel catalyst containing 8% (wt) Al 2O 3 was studied at 220 °C under atmospheric pressure of hydrogen. In the hydrogenolysis of these hydrocarbons the predominant reaction was successive degradation to methane and a hydrocarbon containing one carbon atom less than the starting hydrocarbon. In the case of isoparaffins, only the methyl groups bonded to secondary or tertiary carbon atoms and not those from quarternary carbon atoms were split off. With dialkylcyclohexanes the alkyl groups were successively removed. The cleavage of the cyclohexane ring did not take place under the reaction conditions. The splitting of CC bonds in the side chains of alkylcyclopentanes and alkylcycloheptanes was accompanied by hydrogenolytic opening of the ring. The reactivity of branched-chain hydrocarbons was higher than that of corresponding hydrocarbons containing a straight chain. The high stability of the cyclohexane ring and the higher reactivity of alkylcyclohexanes than that of other alkylcyclanes is explained by the formation and electronic effect of a surface complex of quasiaromatic nature. The differences in the reactivity of hydrocarbons are discussed in terms of the participation of electronic and steric effects.