THE MECHANISM OF CHAIN GROWTH IN THE FISCHER-TROPSCH HYDROCARBON SYNTHESIS

It is proposed that the slow step in chain growth during the Fischer-Tropsch hydrocarbon synthesis is the formation of an adsorbed ethylidene species from two adsorbed methylenes. Addition of a further methylene species gives a diadsorbed C3H6 entity, which leads to a singly attached carbonium ion. A 1,2 hydrogen shift then forms a methyl substituted ethylidene species, which is available for further polymerisation. Further hydrogen shift may occur, yielding an olefin and terminating the chain growth. The extent of chain branching is dictated by the relative stability of secondary and primary carbonium ions, as previously proposed by McCandlish,