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

Abstract

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 sodalite 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.