Adsorption and coadsorption of molecular hydrogen isotopes in zeolites. II. Infrared analyses of H2, HD, and D2 in NaA

Abstract

The infrared analysis of the induced bands of molecular hydrogen isotopes, adsorbed in NaA zeolite, shows several features; (i) when the amount of adsorbed molecules increases, the bands become complex, showing three components, which can be related to different energetic situation of the molecules in the cavity; (ii) the band frequency is lower than the gas frequency; for each species the shifts are proportional to the inverse square root of the mass (same interaction with the crystal); (iii) the absolute intensity increases when the temperature decreases, this is due to the fact that the molecule remains longer in the vicinity of the adsorption site where the electric field is the highest. Its amplitude is deduced from the absolute intensities measured at the lowest temperature (∼1010 V/m, in agreement with other results).

Electric-field-dependent empirical potentials for molecules and crystals: A first application to flexible water molecule adsorbed in zeolites

“…This finding is in line with previous experimental 27,28 and theoretical work, both for natrolite in 29 and for the extended use of relatively small clusters for representing specific sites of zeolites in ab initio calculations, which compare fairly well the full-crystal ones, when available. 57 Work is in progress to refine the potential functions in order to attain a better reproduction of the experimental data and to extend the calculations to zeolites containing different ions or of different structural groups.…”

A review of the computational studies of proton- and metal-exchanged chabazites as media for molecular hydrogen storage performed with the CRYSTAL code

“…New calculations have also been added to the present review, in which the H 2 molecule is described by the aug-ccpVDZ basis set and the framework atoms are treated with a better basis set as described in Ref. [14]. Because, in the present case, the energy of interactions are very small, this better basis set ensures a balanced treatment of all components of the interaction energy.…”

“…Such a difference can be explained on the basis of the local environment of the Na þ cation in the different cases. In the first zeolite, the cation is located in sixmember rings where it is well-coordinated by the surrounding [14,15] Enthalpies are derived from variable-temperature infrared spectroscopy studies and extrapolated at 100 K. Some structural features of the zeolites are also included. Window diameters in Å , frequencies and shifts in cm À1 and enthalpies in kJ/mol.…”

“…The feasibility of this method of storage is basically ruled by the interaction between H 2 and the host material; therefore, the understanding of this interaction is crucial to infer the potential of different materials as storage media. With this objective, several experimental studies on the H 2 interaction with diverse zeolites have been reported in the last years [10,[12][13][14][15][16][17][18][19][20][21][22][23][24][25], focused mainly on the estimation of adsorption enthalpies by means of variable-temperature infrared spectroscopy [26,27]. A summary of the data obtained in these experimental works is presented in Table 1, where it is worth noticing that beside the structural properties of the various studied zeolites (e.g.…”

New frontier in transmission IR spectroscopy of molecules adsorbed on high surface area solids: Experiments below liquid nitrogen temperature

“…As this is the spectral region where the n(HH) mode of molecularly adsorbed H 2 is expected [30,63,[80][81][82][83][84][85][86][87][88][89][90], the authors ascribed the three complex components centered at about 4126-4122, 4099-4093 and 4081-4076 cm À1 to Mg 5c 2+ (H 2 ), Mg 4c 2+ (H 2 ) and Mg 3c 2+ (H 2 ) molecular adducts, respectively. The expected ortho-para splitting (of 6 cm À1 ) is clearly visible for the doublet at 4099-4093 cm À1 , while just results in a band broadening for the remaining two.…”