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

The coordination of extra-framework Li(+) in faujasite (FAU) and the interaction between H(2) 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(+): site SI', the most stable one, in the socialite cage; site SII in the six-ring windows of the sodalite unit and sites SIII and 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' > SII, consistent with the calculated Li-H distance and the charge on H(2). The H-H stretching frequencies of adsorbed species at 4286-4346 cm(-1) are by about 7-67 cm(-1) lower than in the free hydrogen molecules. The small bathochromic harmonic H(2) frequency shift is in agreement with the small H(2) bond elongation. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.