A DFT study of adsorption hydrogen on the Li-FAU zeolite

The coordination of extra-framework Li+Li+ in faujasite (FAU) and the interaction between H2 and Li-FAU were studied by the generalized-gradient approximation (GGA) of density functional theory (DFT) with the Perdew–Burke–Ernzerhof (PBE) exchange-correction functional. Four adsorption sites have been found to be stable for Li+Li+: site SI′SI′, the most stable one, in the sodalite cage; site SII in the six-ring windows of the sodalite unit and sites SIII and SIII′SIII′ in the supercage. Hydrogen interacting with these sites prefers the side-on coordination geometry. Calculated adsorption energies decrease in the sequence of SIII′>SIII>SI′>SIISIII′>SIII>SI′>SII, consistent with the calculated Li–H distance and the charge on H2. The H–H stretching frequencies of adsorbed species at 4286–4346cm-1 are by about 7–67cm-1 lower than in the free hydrogen molecules. The small bathochromic harmonic H2 frequency shift is in agreement with the small H2 bond elongation.