Mechanism of Isomerization of C6-Alkanes over Pt Catalyst

The isomerization of 2, 3-dimethylbutane, 3-methylpentane and methylcyclopentane over Pt-C catalyst was studied at 460°C, under the hydrogen atmospheric pressure.The dehydrogenation was observed with all the hydrocarbons mentioned above before the isomerization took place, and alkenes and cycloalkenes possessing the same skeletal structures as raw materials were produced approximately in thermodynamic equilibrium. Both isomerization and hydrogenolysis were observed to take place to acomparable extent for 2, 3-dimethylbutane and also for 3-methylpentane, whereas isomerization of methylcyclopentane was found extremely limited. Remarkable cyclization was noted only for 3-methylpentane forming methylcyclopentane.The initial isomerization products from 2, 3-dimethylbutane were 2-methylpentane and 2, 2-dimethylbutane. Those from 3-methylpentane were 2-methylpentane, n-hexane and 2, 2-dimethylbutane. The isomerization products from methylcyclopentane were detected in the form of 1, 3-cyclohexadiene and benzene in this study. The formation of 2, 2-dimethylbutane could be explained in terms of the C-C bond shift of sp2-carbon forming a double bond with a surface atom to sp3-carbon in the 1, 3-diadsorbed intermediate.The concurrent formation of methylcyclopentenes and methylenecyclopentane suggested that the cyclization of 3-methylpentane took place via complex pathways, under the conditions used in this study.