| Abstract
| - Cu+-exchanged Si/Al 11:1 chabazite has been studied ab initio using the periodic CRYSTAL03 computercode with Hartree−Fock and the hybrid B3LYP Hamiltonians to characterize the structures and energetics ofthe Cu+ ion sitting preference and its interaction with H2. Two sites (I and IV) have been found to be stablefor Cu+ ion: site I, the most stable one, envisaging coordination in a six-membered zeolite ring and site IVin which the Cu+ ion sits in the largest eight-membered ring. Interaction of H2 gives adsorption energies atB3LYP of −13 and −56 kJ/mol for sites I and IV, respectively. The B3LYP bathochromic harmonic H2frequency shifts are 847 and 957 cm-1 for adsorption at sites I and IV, respectively, in good agreement withthe shifts measured (1030 and 1081 cm-1) in the Cu−ZSM-5 system in which Cu+ ion is, respectively, threeand bi-coordinated by the oxygen atoms of the zeolite framework. Analysis of the components of the adsorptionenergy, carried out within the cluster approach, revealed that charge transfer from the Cu(3dπ) orbital throughthe antibonding H2(σu) and orbital polarization play a significant role in the H2 adsorption energy, and causethe large bathochromic H2 frequency shift.
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