Interaction of Molecular Nitrogen and Oxygen with Extraframework Cations in Zeolites with Double Six-Membered Rings of Oxygen-Bridged Silicon and Aluminum Atoms:  A DFT Study

Abstract

The interaction of N(2) and O(2) with extraframework cations of zeolite frameworks was studied by DFT, using the B3LYP method. The extraframework cation sites located in the vicinity of the double six-member rings (D6R) of FAU zeolites (SI, SI', SIII') were considered and clusters with composition (M(n)(+))(2/)(n)()H(12)Si(10)Al(2)O(18), M = Li(+), Na(+), K(+), Ca(2+), were selected to represent the adsorption centers. The cation sites SII in the center of single six-membered rings (S6R) were modeled by [M(I)H(12)Si(4)Al(2)O(6)](-) and M(II)H(12)Si(4)Al(2)O(6) clusters. The adsorption energy of N(2) and O(2) is the highest for Li(+) cations at the SIII' cation sites, while for the SI' and SII sites the adsorption energies decrease in the order Ca(2+) > Na(+) > Li(+). The calculated small N(2) adsorption energy for Li(+) cations at SII sites suggests that these sites do not take part in the sorption process in agreement with results of NMR studies and Monte Carlo simulations. The N(2) adsorption complexes with the extraframework cations are linear, while those of O(2) are bent regardless of the extraframework cation location. The SIII' cation sites are the most favorable ones with respect to N(2) adsorption capacity and N(2)/O(2) selectivity; the SII sites are less selective and the SI sites are not accessible.

Molecular orbital model of the influence of interaction between O2 and aluminosilicate sites on the triplet–singlet energy gap and reactivity

“…3), we can also show that the O 2 molecule was not on the straight line with the O-H bond of the acid site. These findings are in agreement with the DFT results reported by Mikosch et al [31] who states that O 2 forms a bent structure.…”

“…In a recent study, interactions of O 2 and N 2 with extraframework cations of aluminosilicate materials were investigated using the B3LYP density functional by Mikosch et al [31]. They concluded that the N 2 adsorption complexes with the extraframework cations are linear, while those with O 2 are bent regardless of the extraframework cations location.…”

Thermodynamic study of LiNaKLSX zeolites with different Li exchange rate for N2/O2 separation process

“…These cages enclose large supercages with a free diameter of 12.7 Å. The supercages are accessible via 12 membered-ring windows with a diameter of 7.4 Å [6,7]. The monovalent and divalent extra-framework cations preferentially occupy different crystallographic sites (Fig.…”

“…Adsorption capacity increases in inverse proportion to the size of the compensation cation, i.e. when K + cations are replaced by Na + cations or Na + cations are replaced by Li + cations [6][7][8]. The Si/Al ratio also has an influence and better results were obtained when Si/Al tends to 1 [3,9].…”

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

“…The cluster we choose consists of a sodalite cage and D6Rs, which extend the study by a large series of bare extraframework cations or the clusters limited to S6Rs (a single six-membered ring) or D6Rs [22][23][24]. One framework Si atom was replaced by aluminium and the charge was compensated for by a Li + cation.…”