PFG n.m.r. study of diffusion anisotropy in oriented ZSM-5 type zeolite crystallites

Hong, U.; Kärger, Jörg; Kramer, R.; Pfeifer, H.; Seiffert, G.; Müller, Ulrich; Unger, Klaus K.; Lück, H.B.; Itō, Tarō

doi:10.1016/s0144-2449(05)80061-2

Cited by 88 publications

(51 citation statements)

References 16 publications

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“…When a molecule enters an intersection, it will proceed to one of the four adjacent ones with a probability independent of the channel section from which it has come from. This assumption was not in conflict with the experimental data [7][8][9] and has been, moreover, supported by the evidence of molecular dynamics ͑MD͒ simulations [10][11][12] for simple, spherical molecules like xenon and methane. For sufficiently long alkanes, however, as a consequence of the spatial extension of the molecule, molecular propagation from one channel intersection to the next one cannot be expected anymore to be independent of the trajectory.…”

Section: Introductionsupporting

confidence: 65%

“…As a consequence of the small size of zeolite crystallites, the measurement of diffusion anisotropy either by transient uptake techniques [4][5][6] or by the pulsed field gradient ͑PFG͒ nuclear magnetic resonance ͑NMR͒ method [7][8][9] is subjected to substantial experimental uncertainty, which may be expected to be on the order of magnitude of the effects of correlated motion. Quantitatively, the effect of correlated motion results in an interdependence of the main elements of the diffusion tensor.…”

Section: Introductionmentioning

confidence: 99%

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“Two-step” model of molecular diffusion in silicalite

Kärger

Demontis

Suffritti

et al. 1999

The Journal of Chemical Physics

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The influence of the particle ''memory'' on long-range diffusion in the channel network of silicalite is taken into account by considering pairs of subsequent steps between the channel intersections. It is shown that in this case the correlation rule between the principal elements of the diffusion tensor has to be modified by including an additional term, which takes account of the deviation of molecular propagation from complete randomness. The obtained relations are discussed in terms of molecular dynamics simulations of ethane in silicalite.

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Section: Introductionsupporting

confidence: 65%

Section: Introductionmentioning

confidence: 99%

“Two-step” model of molecular diffusion in silicalite

Kärger

Demontis

Suffritti

et al. 1999

The Journal of Chemical Physics

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“…Once the values of D iso and D ∆ have been quantified, the directional dependence of the signal could be used to estimate the orientation distribution function by, e.g., spherical deconvolution. 54 In its current form, the method is ideal for accurate quantification of diffusion anisotropy in, e.g., lyotropic liquid crystals and porous solids without the need for tedious sample preparation procedures to either completely align the microscopic domains 32 or to assure that they have an isotropic orientation distribution.…”

Section: Discussionmentioning

confidence: 99%

NMR diffusion-encoding with axial symmetry and variable anisotropy: Distinguishing between prolate and oblate microscopic diffusion tensors with unknown orientation distribution

Eriksson

Lasič

Nilsson

et al. 2015

The Journal of Chemical Physics

173

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We introduce a nuclear magnetic resonance method for quantifying the shape of axially symmetric microscopic diffusion tensors in terms of a new diffusion anisotropy metric, DΔ, which has unique values for oblate, spherical, and prolate tensor shapes. The pulse sequence includes a series of equal-amplitude magnetic field gradient pulse pairs, the directions of which are tailored to give an axially symmetric diffusion-encoding tensor b with variable anisotropy bΔ. Averaging of data acquired for a range of orientations of the symmetry axis of the tensor b renders the method insensitive to the orientation distribution function of the microscopic diffusion tensors. Proof-of-principle experiments are performed on water in polydomain lyotropic liquid crystals with geometries that give rise to microscopic diffusion tensors with oblate, spherical, and prolate shapes. The method could be useful for characterizing the geometry of fluid-filled compartments in porous solids, soft matter, and biological tissues.

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“…Using randomly oriented polycrystalline samples greatly increases the complexity of the data analysis. However, if sufficiently large crystals can be synthesized they may be aligned in a single orientation in a matrix of capillary tubes [10]. If the knowledge of the diffusion pattern through the transition metal substituted ZSM-5 could be improved, a better understanding of the different catalytic activity of the metal might result.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Large Crystal Transition Metal Substituted Zeolite ZSM-5

Schaeffer¹,

Kirkby²

2008

TOICJ

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Crystals of ZSM-5 containing Cu, Mn, and Fe have been synthesized up to 85 μm in length along the long axis. This is 1 to 2 orders of magnitude larger than any previously reported. Phase identification was accomplished by powder XRD. A modified Charnel's method was used to chelate the transition metal and the aluminum in the synthesis gel. Elemental analysis was performed by ICP-AES, confirming the presence of the metals. The metals are resistant to leaching under ion exchange and, as determined by partial dissolution, incorporated throughout the volume of the crystals.

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PFG n.m.r. study of diffusion anisotropy in oriented ZSM-5 type zeolite crystallites

Cited by 88 publications

References 16 publications

“Two-step” model of molecular diffusion in silicalite

“Two-step” model of molecular diffusion in silicalite

NMR diffusion-encoding with axial symmetry and variable anisotropy: Distinguishing between prolate and oblate microscopic diffusion tensors with unknown orientation distribution

Synthesis of Large Crystal Transition Metal Substituted Zeolite ZSM-5

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