Subject with zeolite mordenite

Bates et al. (172-174) considered the energetics, locations, and conformations of alkanes ranging from butane to decane in a variety of different all-silica zeolites. Calculations similar to those described already were performed for alkanes in mordenite, zeolite rho, faujasite, ferrierite, and zeolite A. A linear increase in the calculated heat of adsorption with increasing carbon number was found for all zeolites. Less experimental information is available to compare with the calculated heats of adsorption, and thus the performance of the technique and parameters cannot be subjected to quite the same scrutiny as the results for silicalite (111). Nonetheless, where... 

Mass-transfer Effects. - Zeolites possess a large internal surface area and are necessarily subject to mass-transfer effects, although there have been relatively few studies of these. Swabb and Gates observed that for H-mordenite at low temperatures (155°C), rate was independent of crystallite size for methanol dehydration, but at higher temperature rate variation was consistent with a Thiele model. 

Microcalorimetric studies of several zeolites (H-mordenite, USY, H-ZSM-5), treated in such a way as to contain a noticeable amount of extra-framework aluminum, have shown that the distribution of the sites with respect to the differential heats of NH3 adsorption is exponential for the I wis sites (Freundlich isotherm) and linear for the Brdnsted sites (Temkin isotherm) [82,83]. In most cases, the catalytic activity is related to the number of Brdnsted sites rather than Lewis acid sites. However, the influence of acidic Lewis sites in catalytic reactions over zeolites is still subject to controversy and cannot be neglected. 

In some instances the materials were also repeatedly subjected to this two-step treatment to enhance the degree of dealumination, e.g., in [89]. In the case of zeolites resistant to acids due to high framework Si/Al ratios, e.g.,mordenite and ZSM-5, acid leaching may also precede the hydrothermal treatment [ 10,23]. In this case, healing of framework hydroxyl nests left by aluminum release is the lattice-stabilizing process. The hydrothermal stability of steamed Y zeolites was found to increase upon removal of extra-framework aluminum by extraction with acids [94]. 

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