Molecular dynamics studies on zeolites.  4.  Diffusion of methane in silicalite

Demontis, Pierfranco; Fois, Ettore; Suffritti, Giuseppe Baldovino; Quartieri, Simona

doi:10.1021/j100373a083

Cited by 179 publications

(99 citation statements)

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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: 64%

“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: 64%

“Two-step” model of molecular diffusion in silicalite

Kärger

Demontis

Suffritti

et al. 1999

The Journal of Chemical Physics

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“…We have previously devised a ''two-step'' model for the molecular diffusion in silicalite, which considerably improves the random-walk description of the diffusion of ethane at different loading and temperature 15 and of linear diatomic and triatomic flexible molecules at infinite dilution. 16 This observation shows that, while the RW uncorrelated picture may be appropriate in the case of small spherical sorbates such as methane and xenon, 1,[17][18][19][20] the motion of small linear species in silicalite can exhibit significant correlation effects. The two-step model merges each pair of two successive displacements between channel intersections and represents the molecular motion as a sequence of such double steps.…”

Section: Introductionmentioning

confidence: 97%

Two- and N-step correlated models for the analysis of molecular dynamics trajectories of linear molecules in silicalite

Demontis

Suffritti

Tilocca

2000

The Journal of Chemical Physics

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Recent molecular dynamics data on the diffusion of linear diatomic and triatomic molecules in the zeolite silicalite are analyzed in terms of a new correlated model ͓F. Jousse, S. M. Auerbach, and D. P. Vercauteren, J. Chem. Phys. 112, 1531 ͑2000͔͒ capable to account for both first-and higher-order correlation effects. This ''N-step'' model reproduces very well our calculated mean square displacements and diffusion coefficients of the molecules considered. The improvements with respect to the results obtained with our previous ''two-step'' model ͓P. Demontis, J. Kärger, G. B. Suffritti, and A. Tilocca, Phys. Chem. Chem. Phys. 2, 1455 ͑2000͔͒ are remarkable for all molecules except chlorine, showing that only in this case the effect of ͑negative͒ correlations spanning more than two jumps between channel intersections ͑ϳ20 Å͒ can be neglected. The basic trajectory analysis in terms of single-and two-step models, besides being an useful reference, provides all the input data needed for the application of the N-step model. Indeed, in its silicalite formulation, the N-step model is strongly linked to the two-step one because it calculates the probability of a sequence of jumps in the same channel by means of the correlations between any two consecutive jumps. Finally, the possibility to obtain qualitative insight into the diffusive mechanism through various kind of correlation coefficients is discussed.

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“…Zeolite pores are narrow as the pore width is usually smaller than 1.5 nm. An accurate textural characterization of microporous materials is of crucial importance for their application, for example in catalysis and separation technology [6,7,8,9,10]. The pore architecture, i.e.…”

Section: Introductionmentioning

confidence: 99%