Application of Density Functional Theory to Al Distribution in Mordenite

Abstract

Mordenite zeolites are well known for their acid cracking abilities, but are often hindered by coke formation which limits their life. The dealumination and generation of Bronsted acid sites in the MOR structure will have significant implications as to their catalytic activity. Density functional theory (DFT) has been applied to determine preferred aluminum siting in the Na-mordenite zeolite structure. DFT correctly reproduces the 6–31G* Hartree-Fock predictions for the relative stabilities of the four T sites of mordenite in a T(OH)4 cluster. Larger cluster sizes influence the preferred Al siting with DFT predicting T2 as the preferred tetrahedral site. Since DFT computational requirements are considerably smaller than Hartree-Fock theory, it is an attractive alternative for studying zeolites. The calculations performed were based on fixed geometries obtained from crystallographic data. Further work employing local geometry optimization in the vicinity of the substituted Al is underway.

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Acknowledgments

The authors wish to thank Cray Research, Inc. for a generous allocation of computer time and for access to the UniChem software package. We wish to thank Air Products and Chemicals, Inc. for permission to publish this work.

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Correspondence to G. Fitzgerald.

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Fitzgerald, G., Coe, C., Klotz, H. et al. Application of Density Functional Theory to Al Distribution in Mordenite. MRS Online Proceedings Library 291, 239–245 (1992). https://doi.org/10.1557/PROC-291-239

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