What do vanadium framework sites look like in redox model silicate zeolites?

Ab initio periodic DFT Calculations on the structural and energy properties of different model vanadium framework sites in vanadium-substituted zeolites containing sodalite cavities are presented and related to experimental FTIR measurements on V containing SiBEA zeolite. The vanadium framework sites are characterized by their calculated geometrical parameters, vibrational frequencies and deprotonation energies. Vanadium(V) is stabilized in the zeolite framework in two different tetrahedral sites: one in the form of a very stable vanadyl group and the other possessing a hydroxyl group. Tetrahedral vanadium(IV) sites, although much less favorable, are also present with a acidic hydroxyl group. Hydration of vanadium-substituted zeolites is an athermic process. Water does not affect the coordination of vanadium and remains in the center of the cavity. These results are fully consistent with experimental data and allow to identify the molecular structure of vanadium sites in a zeolite framework. (C) 2008 Elsevier Inc. All rights reserved.