Regioselectivity of Al–O Bond Hydrolysis during Zeolites Dealumination Unified by Brønsted–Evans–Polanyi Relationship

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 tetra-coordinated 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