The mechanism of dehydrocyclization has been investigated with a group of branched C6 and C7 isomeric hydrocarbons containing only four or five carbon atoms in the main chain on Ni and Co catalysts of small and medium dispersion in the temperature range 573-650 K. At low H2 HC ratios transformation of 2-methylpentane, 3-methylpentane, and 3-ethylpentane yields toluene and ethylbenzene, respectively, besides benzene. Evidence is presented that the formation of benzene takes place via CHx-addition to a vinylic group, 1,6-ring closure, and CHx-abstraction in the adsorbed phase. In the proposed reaction sequence the rate of CHx insertion is regarded as the rate-limiting step of aromatization. Participation of the bond-shift or the C5-cyclization route of aromatization is not significant over Ni and Co.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry