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

The experimental determination of Al siting in zeolites involves the u se of multiple techniques. Great effort has been made on both, experim ental and theoretical approaches. The present study presents a novel m ethodology for calculating Al/Si replacement energies. Simple semiempi rical calculations were applied on Modenite, Ferrierite and ZSM-5 zeol ites, resulting in good agreement with the experimetal evidences. We h ave found that the favored Al substitution sites are T3 and T4 in Mord enite, while T2 and T4 are in Ferrierite, and only the T9 site is favo red in ZSM-5. The method presented is based on an average of partial A l/Si replacement energies, evaluated for all rings belonging to each T site, rather than in the calculation of a total replacement energy ev aluated for only one representative aggregate.