Mikosch Hans, Uzunova Ellie L, St Nikolov Georgi
Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9/E164/EC, Vienna A-1060, Austria.
J Phys Chem B. 2005 Jun 9;109(22):11119-25. doi: 10.1021/jp0451795.
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.
采用密度泛函理论（DFT）中的B3LYP方法，研究了N₂和O₂与沸石骨架外阳离子的相互作用。考虑了位于FAU沸石双六元环（D6R）附近的骨架外阳离子位点（SI、SI'、SIII'），并选取组成式为(Mₙ⁺)₂/ₙH₁₂Si₁₀Al₂O₁₈（M = Li⁺、Na⁺、K⁺、Ca²⁺）的团簇来代表吸附中心。单六元环（S6R）中心的阳离子位点SII用[M(I)H₁₂Si₄Al₂O₆]⁻和M(II)H₁₂Si₄Al₂O₆团簇进行建模。对于SIII'阳离子位点的Li⁺阳离子，N₂和O₂的吸附能最高，而对于SI'和SII位点，吸附能按Ca²⁺ > Na⁺ > Li⁺的顺序降低。计算得出Li⁺阳离子在SII位点的N₂吸附能较小，这表明这些位点不参与吸附过程，这与核磁共振研究和蒙特卡罗模拟的结果一致。与骨架外阳离子形成的N₂吸附络合物是线性的，而O₂的吸附络合物无论骨架外阳离子位置如何都是弯曲的。就N₂吸附容量和N₂/O₂选择性而言，SIII'阳离子位点是最有利的；SII位点选择性较低，而SI位点不可达。
