We determine the mechanism of the initiation of Al−O(H) bond breaking for zeolitic structures mordenite (MOR), faujasite (FAU), MFI, and chabazite (CHA) with high Si/Al ratio occurring during dealumination. Periodic density functional theory calculations demonstrate that water adsorption on the Al atom takes place in anti position to the Brønsted acid site, via a penta-or tetracoordinated Al species. A subsequent 1,2-dissociation of water on adjacent framework oxygen atoms leads to the first Al−O(H) bond breaking (with activation energies of ∼76−125 kJ/mol). A Brønsted−Evans−Polanyi relationship to estimate transition states (TS) is established and opens the door to predictions of which crystallographic sites are able to initiate dealumination.

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