Hydrogenolysis of saturated hydrocarbons: III. Selectivity in hydrogenolysis of various aliphatic hydrocarbons on platinum/alumina

Abstract

The reactions with hydrogen of various aliphatic hydrocarbons ranging from C 4 to C 8 have been studied over Pt Al 2O 3 as catalyst. The main reaction is hydrogenolysis, parallel isomerization and dehydrocyclization being very slow if the hydrocarbon chain is less than four carbon atoms long. Whenever 1,5-diadsorbed species can be formed, the rates of isomerization and dehydrocyclization are increased. The rates of hydrogenolysis of a variety of different carbon-carbon bonds have been measured and tabulated. The reactivity of a bond depends not only on the substitution of the two carbon atoms involved, but also on the substitution of the neighboring atoms. Bonds in the β position to a tertiary carbon atom are extensively broken. On the contrary, with a quaternary carbon atom, the hydrogenolysis in the α position to this atom is more rapid than in the β position. The results cannot all be rationalized by a single reaction mechanism, but support the view that 1,2-, 1,3-, 1,4-, and 1,5-diadsorbed species can all play a role in reaction between hydrogen and hydrocarbons on platinum.