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H. Mikosch, E. Uzunova, G. Nikolov:
"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";
Journal of Physical Chemistry B, 109 (2005), S. 11119 - 11125.

The interaction of N2 and O2 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 (Mn+)2/nH12Si10Al2O18, M = Li+, Na+, K+, Ca2+, were selected to represent the adsorption centers. The cation sites SII in the center of single six-membered rings (S6R) were modeled by [MIH12Si4Al2O6]- and MIIH12Si4Al2O6 clusters. The adsorption energy of N2 and O2 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 Ca2+ > Na+ > Li+. The calculated small N2 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 N2 adsorption complexes with the extraframework cations are linear, while those of O2 are bent regardless of the extraframework cation location. The SIII' cation sites are the most favorable ones with respect to N2 adsorption capacity and N2/O2 selectivity; the SII sites are less selective and the SI sites are not accessible.

http://dx.doi.org/10.1021/jp0451795

http://pubs.acs.org/cgi-bin/article.cgi/jpcbfk/2005/109/i22/html/jp0451795.html