Sorption of light alkanes on H-ZSM5 and H-mordenite

The sorption of light n- and iso-alkanes on H-ZSM5 and H-MOR was studied by means of calorimetry, gravimetry and in situ infrared spectroscopy. Alkanes sorb preferentially localized on the strong Brønsted acid sites of H-ZSM5 and H-MOR. Two n-alkane, but only one iso-alkane molecule can be simultaneously accommodated on the Brønsted acid sites of H-ZSM5. In contrast, only one alkane molecule interacts with a strong Brønsted acid site of H-MOR, and, moreover, only a third of these sites are strongly interacting at all with alkanes because of steric reasons. For both zeolites, the heat of adsorption increases with increasing size of the hydrocarbon. The linear relationship between the enthalpies and the entropies of sorption suggests that the molecular motions of the sorbed molecules are restricted in proportion to the strength of interaction with the zeolite.