Simulating non-framework cation location in aluminosilicate zeolites

Newsam, J. M.; Freeman, C. M.; Gorman, A. M.; Vessal, B.

doi:10.1039/cc9960001945

Cited by 31 publications

(19 citation statements)

References 8 publications

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“…For probing the host−guest potential energy surface, we used a simple methodology combining the packing of a guest molecule into the zeolitic host structure followed by a fixed-lattice energy minimization of the host−guest system. This is often referred to as the Monte Carlo packing procedure; it has been successfully used for probing the binding sites of organic molecules in microporous sorbents , and was extended more recently to the study of cation positioning in zeolites. , The calculations are equivalent to 0 K calculations for a single sorbate molecule and correspond to the zero-coverage limit.…”

Section: Computational Approachmentioning

confidence: 99%

Localization of Adsorbed Cyclohexane in the Acid Form of Zeolite Y. A Powder Neutron Diffraction and Computational Study

1997

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The crystal structure of the deuterated acid form of zeolite Y with adsorbed cyclohexane (∼1 molecule/supercage) has been determined by powder neutron diffraction at 5 K. The structure was refined by the Rietveld least-squares method in the cubic space group Fd3m [a = 24.711(2) Å, R p = 3.13%, Rwp = 4.28%]. Deuterium atoms were located, in order of decreasing occupancy, on O(3)[33(3)%], O(1)[10(2)%], O(4)[3(3)%] and O(2)[2(3)%]. Approximately half of the adsorbed cyclohexane molecules were located in the chair conformation in the 12-ring window. Energy minimization calculations predict various types of binding sites for cyclohexane in siliceous Y. One type of site is found in the 12-ring window and is in excellent agreement with the position determined from the diffraction analysis. Other binding sites in low-symmetry positions are predicted, where cyclohexane is coordinated to 4-ring and 6-ring windows; these could not be detected by the diffraction analysis. Our calculations suggest that cyclohexane molecules experience a rather flat potential surface in zeolite Y.

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Section: Computational Approachmentioning

confidence: 99%

Localization of Adsorbed Cyclohexane in the Acid Form of Zeolite Y. A Powder Neutron Diffraction and Computational Study

1997

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“…15,[18][19][20][21] Theoretical models 10,[22][23][24][25][26][27] and computational approaches have also been used to predict cation location in this material 13,[28][29][30][31] as well as in other zeolites. [48][49][50] The cation distribution is usually described as follows (see Figure 1). Na + can occupy sites I, located in the hexagonal prisms which connect sodalite cages.…”

Section: Introductionmentioning

confidence: 99%

Distribution of Sodium Cations in Faujasite-Type Zeolite: A Canonical Parallel Tempering Simulation Study

et al. 2003

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A Monte Carlo replica exchange (MCRE) algorithm was used to compute the sodium cation distribution in bare faujasite zeolite with a number of cations per unit cell ranging from zero (Si:Al → ∞) to 96 (Si:Al = 1). Eight independent realizations of the system were simulated simultaneously, in the temperature range 300-2325 K. The resulting distributions at room temperature were found to be in very good agreement with both available experiments and the analytical quasi-chemical model of Mortier and co-workers. A single canonical simulation at room temperature using site-to-site hopping yields identical results. The main advantage of the MCRE method is that no assumption is needed on the actual cation adsorption sites. One could thus, in principle, predict cation locations and distributions in a nanoporous solid for which the precise location of extraframework cations is not known.

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“…A variety of theoretical and computational studies have been reported on the locations of cations in zeolites. Mortier and co-workers have developed lattice models to rationalize the temperature dependence of experimentally determined cation site occupancies. , Off-lattice Monte Carlo simulations have also been performed to explain and predict cation occupancies ,− and ordering in zeolites. Electronic structure calculations have been performed to generate potential energy surfaces for cation−frame interactions in sodalite-type zeolites .…”

Section: Introductionmentioning

confidence: 99%

New Force Field for Na Cations in Faujasite-Type Zeolites

1999

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We have developed and validated a new force field for cations in zeolites, which explicitly distinguishes Si and Al atoms, as well as different types of oxygens in the framework. Our new force field gives excellent agreement with experimental data on cation positions, site occupancies and vibrational frequencies. Energy minimizations show that Na cations in site I are not at the centers of hexagonal prisms, but rather are in one of two symmetric S I sites displaced by about 0.6 Å along the [111] direction. Molecular dynamics (MD) simulations show that most cations are immobile in Na-X and Na-Y on the MD time scale, even at 1000 K. Only Na-X cations in site III′ exhibit diffusive motion at 1000 K, with a self-diffusivity from MD of 3.6 × 10 -10 m 2 s -1 . The MD simulations also show that cation movement is highly correlated, composed of jumps involving at least 4 cations or more.

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Simulating non-framework cation location in aluminosilicate zeolites

Cited by 31 publications

References 8 publications

Localization of Adsorbed Cyclohexane in the Acid Form of Zeolite Y. A Powder Neutron Diffraction and Computational Study

Localization of Adsorbed Cyclohexane in the Acid Form of Zeolite Y. A Powder Neutron Diffraction and Computational Study

Distribution of Sodium Cations in Faujasite-Type Zeolite: A Canonical Parallel Tempering Simulation Study

New Force Field for Na Cations in Faujasite-Type Zeolites

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