Petroleum Chemistry, Vol.41, No.6, 383-394, 2001
The mechanism of selective aromatization of hexane to benzene on zeolite catalysts
Results of chemical transformations of n-hexane on modified acid zeolite catalysts in a hydrogen atmosphere at low conversions were considered. The catalyzate of a simpler composition, in which aromatic hydrocarbons were presented only by benzene or by benzene and toluene with C6H6 predominance, was obtained on certain specimens. Methane, n-butane, n-pentane, 2,2-dimethylpentane, and methylcyclopentane were also present, but neither ethane, nor propane, nor C-8-C-10 or higher aromatic hydrocarbons were found. It was suggested that on such selective catalysts n-hexane is protonated at the first carbon atom to afford supersaturated nonclassic carbocations C6H15+ with the following deep dehydrogenation to unsaturated primary carbocations C6H7+, which directly close to give benzene rings. The carbocations C6H15+ with a charge on the second carbon atom, which are formed as a result of isomerization of the primary nonclassic carbocations, play the determining role in the formation of other products. The formation pathways of all major products found in the catalyzates of the selectively operating specimens are analyzed.