Interaction of H2 with Alkali-Metal-Exchanged Zeolites: a Quantum Mechanical Study

Recently, zeolites have been proposed as media for hydrogen by means of molecular adsorption. The interaction of a dihydrogen molecule on alkali metal ions in high-silica zeolites has been theoretically studied in cluster and periodic models at the B3-LYP level of theory. The cluster models have been obtained by embedding Li+, Na+, and K+ in aluminosilicate rings of different sizes (Sin-1AlOnH2n, 4 <= n <= 6). The structure of Li, Na, and K-exchanged chabazite with Si/Al = 11:1 has been adopted as the periodic model. In both cases, the hydrogen molecule interacts side-on with the cations, forming T-shaped complexes. The results have been compared with similar data obtained for bare cations and previous experimental studies. Furthermore, the necessity of employing correlated methods for a proper description of the interaction has been verified at the MP2 level.