Influence of the Zeolite Topology

The topology of the zeolite host is also crucial for the diffusion of the guest through the interior it controls the maximum uptake achievable. Zeolites with tridi-rectional structures are more accessible and allow diffusion readily, whereas diffusion in monodirectional zeolites is seriously affected [68]. 

Influence of structure on the number and strength of available Brdnsted acid sites was investigated on a series of dealuminated zeolites (HY, mordenite, ZSM-5 and 

Contrary to this behavior, various structures with high Si/Al ratio (H-ZSM-5, H-ZSM-12, HY and H-mordenite) were found to exhibit almost the same adsorption energies measured at 480 K, suggesting that the isolated Bronsted acid sites in these materials are identical [76]. Authors observed that the strength of Bronsted acid sites associated with framework A1 atoms does not vary in a given zeolite, and they suggest that Bronsted acid sites in unsteamed zeolites are independent of the sample (what means, independent of Si/ A1 ratio) and equal in concentration to the framework aluminum content [77]. 

Dlltaienllil Heat (KJtmal) Differential Heal (kjfn )l) 

It can be concluded that the heat curves should be similar only when the solids contain exlusively isolated sites where the next-nearest neighbors (NNN) are identical. It appears that the NNN determines Bronsted acidity, in fact, it can be said that zeolite geometry has an influence on acidity due to long-range effects as well as on the local structure of the acid sites. 

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