Reactions of hexane and 3-methylpentane on HZSM-5 at moderate temperatures in liquid phase and gas phase [1

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The reactivity of 3-methylpentane (3MP) and hexane (H) on HZSM-5 at 120–160 °C changes from gas (H > 3MP) to liquid phase (3MP > H), as does product selectivity. The liquid phase reactivity ratio is similar on HZSM-5 and in trifluoromethanesulfonic acid (TFMSA), where the reaction involves initiation by oxidation to allyl cations. In both cases, olefins are intermediates, but do not appear in the products. Because hydride transfer catalysis is absent in the reaction of H and the steric requirements for hydride transfer are smaller than for cracking, the mechanism involving protonation of sigma bonds, as in liquid superacids, does not operate in zeolites. The H:3MP reactivity ratio does not measure steric constraints in cavities.