Methylcyclohexane transformation over HFAU, HBEA, and HMFI zeolites: I. Reaction scheme and mechanisms

The transformation of methylcyclohexane was investigated at 450 degreesC fo r several contact times over six previously characterized HFAU, HMFI, and H BEA zeolites having framework Si/AI ratios either close to 15 or between 26 and 47. With all of the fresh samples, C-2-C-7 alkenes and alkanes, cyclop entane and methylcyclopentane (cracking products), dimethylcyclopentanes an d ethylcyclopentane (isomers), and aromatics appear as primary products. Hy drogen and methane are also directly formed (methylcyclohexane protolysis) with HBEA-15, which presents very strong protonic sites, and with HMFI samp les. A simplified kinetic model was established, and the rate constants lea ding to good agreement between experimental data and calculated yields of t he main products were determined. Large differences in the rate constants a re observed between the zeolite samples, which can be related to difference s in acid strength and particularly to a pronounced influence of the zeolit e pore structure.