Analysis of MD trajectories as a jump diffusion process: Butene isomers in zeolite types TON and MEL

Research output: Contribution to journalArticle

Abstract

We have studied, by molecular dynamics, the self-diffusion of the four butene isomers in zeolite types TON and MEL at 623 K, for several loadings. Even if both systems present low-energy barriers to the diffusion (less than 10 kJ/mol), an essential difference appears between the two zeolite types. On one hand, TON presents unidirectional straight channels, and therefore there is almost no change of entropy during the migration of a guest molecule in the channel, so that their most probable position at 623 K corresponds to their minimum energy position. On the other hand, MEL presents intersecting straight channels, and while the minimum energy positions are located in the channels, the most probable positions are at the intersections, due to entropy effects which are larger than the energy change at 623 K. Using transition rate constants for siteto-site jumps estimated from the molecular dynamics trajectories, we have modeled the behavior of the four isomers of butene by a jump diffusion model (JDM). This appears to reproduce reasonably well their meansquare displacement in zeolite MEL, both at infinite dilution and at nonzero loading, due to the high free energy barriers attributed to the entropy effects. In zeolite TON, the self-diffusivities computed from a JDM are systematically underestimated as compared to those computed by molecular dynamics, due to the insufficient thermalization of the molecules. To better represent this diffusion mechanism, we have introduced a correlated jump diffusion model that accounts for insufficient thermalization by supposing that a given molecule has a larger probability to jump in the same direction as its previous jump than in the reverse direction. This correlated jump diffusion model reproduces well the diffusivity of cis-2-butene and isobutene in zeolite TON, but not that of trans-2-butene and 1 -butene. The difference probably originates in the "fitting" of the guest molecules in the channels, as well as the guest-guest interactions.
Original languageEnglish
Pages (from-to)4717-4732
Number of pages16
JournalJournal of physical chemistry B
Volume101
Publication statusPublished - 12 Jun 1997

Fingerprint

Butenes
Isomers
Trajectories
Molecular dynamics
Molecules
Entropy
Energy barriers
Free energy
Dilution
Rate constants

Cite this

@article{1b67044c2e994e3f80c7db579db714cd,
title = "Analysis of MD trajectories as a jump diffusion process: Butene isomers in zeolite types TON and MEL",
abstract = "We have studied, by molecular dynamics, the self-diffusion of the four butene isomers in zeolite types TON and MEL at 623 K, for several loadings. Even if both systems present low-energy barriers to the diffusion (less than 10 kJ/mol), an essential difference appears between the two zeolite types. On one hand, TON presents unidirectional straight channels, and therefore there is almost no change of entropy during the migration of a guest molecule in the channel, so that their most probable position at 623 K corresponds to their minimum energy position. On the other hand, MEL presents intersecting straight channels, and while the minimum energy positions are located in the channels, the most probable positions are at the intersections, due to entropy effects which are larger than the energy change at 623 K. Using transition rate constants for siteto-site jumps estimated from the molecular dynamics trajectories, we have modeled the behavior of the four isomers of butene by a jump diffusion model (JDM). This appears to reproduce reasonably well their meansquare displacement in zeolite MEL, both at infinite dilution and at nonzero loading, due to the high free energy barriers attributed to the entropy effects. In zeolite TON, the self-diffusivities computed from a JDM are systematically underestimated as compared to those computed by molecular dynamics, due to the insufficient thermalization of the molecules. To better represent this diffusion mechanism, we have introduced a correlated jump diffusion model that accounts for insufficient thermalization by supposing that a given molecule has a larger probability to jump in the same direction as its previous jump than in the reverse direction. This correlated jump diffusion model reproduces well the diffusivity of cis-2-butene and isobutene in zeolite TON, but not that of trans-2-butene and 1 -butene. The difference probably originates in the {"}fitting{"} of the guest molecules in the channels, as well as the guest-guest interactions.",
author = "F. Jousse and Laurence Leherte and Daniel Vercauteren",
note = "Copyright 2004 Elsevier Science B.V., Amsterdam. All rights reserved.",
year = "1997",
month = "6",
day = "12",
language = "English",
volume = "101",
pages = "4717--4732",
journal = "Journal of physical chemistry B",
issn = "1089-5647",
publisher = "American Chemical Society",

}

TY - JOUR

T1 - Analysis of MD trajectories as a jump diffusion process

T2 - Butene isomers in zeolite types TON and MEL

AU - Jousse, F.

AU - Leherte, Laurence

AU - Vercauteren, Daniel

N1 - Copyright 2004 Elsevier Science B.V., Amsterdam. All rights reserved.

PY - 1997/6/12

Y1 - 1997/6/12

N2 - We have studied, by molecular dynamics, the self-diffusion of the four butene isomers in zeolite types TON and MEL at 623 K, for several loadings. Even if both systems present low-energy barriers to the diffusion (less than 10 kJ/mol), an essential difference appears between the two zeolite types. On one hand, TON presents unidirectional straight channels, and therefore there is almost no change of entropy during the migration of a guest molecule in the channel, so that their most probable position at 623 K corresponds to their minimum energy position. On the other hand, MEL presents intersecting straight channels, and while the minimum energy positions are located in the channels, the most probable positions are at the intersections, due to entropy effects which are larger than the energy change at 623 K. Using transition rate constants for siteto-site jumps estimated from the molecular dynamics trajectories, we have modeled the behavior of the four isomers of butene by a jump diffusion model (JDM). This appears to reproduce reasonably well their meansquare displacement in zeolite MEL, both at infinite dilution and at nonzero loading, due to the high free energy barriers attributed to the entropy effects. In zeolite TON, the self-diffusivities computed from a JDM are systematically underestimated as compared to those computed by molecular dynamics, due to the insufficient thermalization of the molecules. To better represent this diffusion mechanism, we have introduced a correlated jump diffusion model that accounts for insufficient thermalization by supposing that a given molecule has a larger probability to jump in the same direction as its previous jump than in the reverse direction. This correlated jump diffusion model reproduces well the diffusivity of cis-2-butene and isobutene in zeolite TON, but not that of trans-2-butene and 1 -butene. The difference probably originates in the "fitting" of the guest molecules in the channels, as well as the guest-guest interactions.

AB - We have studied, by molecular dynamics, the self-diffusion of the four butene isomers in zeolite types TON and MEL at 623 K, for several loadings. Even if both systems present low-energy barriers to the diffusion (less than 10 kJ/mol), an essential difference appears between the two zeolite types. On one hand, TON presents unidirectional straight channels, and therefore there is almost no change of entropy during the migration of a guest molecule in the channel, so that their most probable position at 623 K corresponds to their minimum energy position. On the other hand, MEL presents intersecting straight channels, and while the minimum energy positions are located in the channels, the most probable positions are at the intersections, due to entropy effects which are larger than the energy change at 623 K. Using transition rate constants for siteto-site jumps estimated from the molecular dynamics trajectories, we have modeled the behavior of the four isomers of butene by a jump diffusion model (JDM). This appears to reproduce reasonably well their meansquare displacement in zeolite MEL, both at infinite dilution and at nonzero loading, due to the high free energy barriers attributed to the entropy effects. In zeolite TON, the self-diffusivities computed from a JDM are systematically underestimated as compared to those computed by molecular dynamics, due to the insufficient thermalization of the molecules. To better represent this diffusion mechanism, we have introduced a correlated jump diffusion model that accounts for insufficient thermalization by supposing that a given molecule has a larger probability to jump in the same direction as its previous jump than in the reverse direction. This correlated jump diffusion model reproduces well the diffusivity of cis-2-butene and isobutene in zeolite TON, but not that of trans-2-butene and 1 -butene. The difference probably originates in the "fitting" of the guest molecules in the channels, as well as the guest-guest interactions.

UR - http://www.scopus.com/inward/record.url?scp=0000519822&partnerID=8YFLogxK

M3 - Article

VL - 101

SP - 4717

EP - 4732

JO - Journal of physical chemistry B

JF - Journal of physical chemistry B

SN - 1089-5647

ER -