Monomolecular conversion of light alkanes over H-ZSM-5

The monomolecular conversion of light n-alkanes (propane to n-hexane) over H-ZSM-5 was investigated between 723 and 823 K. The rates and energies of activation of the individual reactions were determined and a kinetic model for the conversion is presented. The results suggest that carbonium ions are intermediates for all primary reactions. Depending upon the nature of the carbonium ion in the transition state, three parallel primary reactions were identified, leading to hydrogen exchange, dehydrogenation, and cracking. With increasing size of the n-alkane, the rate of reaction increases due to the increase in the adsorption constant of the hydrocarbon. The true energies of activation are independent of the hydrocarbon chain length and the position of the carbon-carbon bond to be cleaved.