THEORETICAL CALCULATIONS ON ZEOLITES - THE ALUMINUM SUBSTITUTION IN MORDENITE, FERRIERITE AND ZSM-5

The experimental determination of Al siting in zeolites involves the use of multiple techniques. Great effort has been made on both, experimental and theoretical approaches. The present study presents a novel methodology for calculating Al/Si replacement energies. Simple semiempirical calculations were applied on Modenite, Ferrierite and ZSM-5 zeolites, resulting in good agreement with the experimetal evidences. We have found that the favored Al substitution sites are T3 and T4 in Mordenite, while T2 and T4 are in Ferrierite, and only the T9 site is favored in ZSM-5. The method presented is based on an average of partial Al/Si replacement energies, evaluated for all rings belonging to each T site, rather than in the calculation of a total replacement energy evaluated for only one representative aggregate.