Zeolite predicted frequencies

The hydroxyl groups of the first kind are already absent in faujasites, quite in accordance with the cluster model predictions. Instead, two other bands with fundamental stretching vibration frequencies of 3640 and 3650 cm-1 were observed in Y zeolites. They were assigned to OH-II groups located within the large cavities (3650 cm 1) and to OH-II groups positioned inside the hexagonal prisms (3555 cm 1) (82). 

For the conversion of m-xylene, the activity of H-faujasite depends strongly on its degree of dealumination. Maximum catalytic activity is obtained for aluminum T-atom fractions equal to 0.10. Surprisingly, in contrast to both theoretical predictions and to the behaviour of H-ZSM-5, for dealuminated H-faujasites the turnover frequency per protonic aluminum site exhibits a pronounced maximum when the aluminum T-atom fraction is 0.09. The present results can be rationalized if, besides the classical predictions on zeolite acidity, a new concept of "hidden acid sites" is handled. Changes of the m-xylene isomerisation and disproportionation selectivities with the degree of dealumination of faujasite are in agreement with this concept. 

All theoretical models on zeolite acidity predict that the acid strength, and consequently the turnover frequency decreases with increasing aluminum T-atom... 

P-24 - Theoretical prediction of IR spectra of guest molecules in zeolites the stretching frequency of CO adsorbed at various cationic sites in ZSM-5... 

The atomic multipole expansion of the BI electrostatic potential is extremely useful, when the long-range, purely point-multipolar part of the potential yields an important contribution. This is the case in crystals, where the multipolar sums (up to the quadrupolar potential) are conditionally convergent lattice sums. Special techniques, like Ewald summation method [130, 131] and its generalizations [132] are needed to handle properly these infinite sums. Recently we applied the multipolar BI method, coupled with Ewald summation for the evaluation of electrostatic potentials and fields in zeolite cavities [133] and for the prediction of the IR frequency sequence of the different acidic sites in H-faujasite [134]. 

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