Molecular Dynamics Simulations of Self-Diffusivities, Corrected Diffusivities, and Transport Diffusivities of Light Gases in Four Silica Zeolites To Assess Influences of Pore Shape and Connectivity

Skoulidas, Anastasios I.; Sholl, David S.

doi:10.1021/jp0354301

Cited by 184 publications

(236 citation statements)

References 42 publications

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“…For methane in MFI-type zeolite, support for the concentration independence was found almost up to high, but not maximum loading. 1,33 B. Lattice Models and Correlations. Diffusion is often studied by considering particles' movements as a hopping process on a lattice.…”

Section: Diffusion Theorymentioning

confidence: 99%

“…1,2,5,6,24,55,56 Zeolites exist in a wide variety of structures. Currently, over 130 different topologies are known.…”

Section: Zeolite Structuresmentioning

confidence: 99%

“…This makes the diffusion behavior of adsorbed molecules in these materials very different from diffusion in a bulk fluid. [1][2][3][4][5][6][7][8][9][10] Although these systems are well-studied, their diffusion properties remain poorly understood. An intensive research effort to measure diffusion rates in nanoporous materials augmented the possibilities of determining diffusion rates in nanoporous materials, such as zeolites, metal-organic frameworks, ion channels, etc.…”

Section: Introductionmentioning

confidence: 99%

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Loading Dependence of the Diffusion Coefficient of Methane in Nanoporous Materials

2006

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In this work, we use molecular simulations to study the loading dependence of the self-and collective diffusion coefficients of methane in various zeolite structures. To arrive at a microscopic interpretation of the loading dependence, we interpret the diffusion behavior in terms of hopping rates over a free-energy barrier. These free-energy barriers are computed directly from a molecular simulation. We show that these free-energy profiles are a convenient starting point to explain a particular loading dependence of the diffusion coefficient. On the basis of these observations, we present a classification of zeolite structures for the diffusion of methane as a function of loading: three-dimensional cagelike structures, one-dimensional channels, and intersecting channels. Structures in each of these classes have their loading dependence of the free-energy profiles in common. An important conclusion of this work is that diffusion in nanoporous materials can never be described by one single effect so that we need to distinguish different loading regimes to describe the diffusion over the entire loading range.

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Section: Diffusion Theorymentioning

confidence: 99%

“…1,2,5,6,24,55,56 Zeolites exist in a wide variety of structures. Currently, over 130 different topologies are known.…”

Section: Zeolite Structuresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Loading Dependence of the Diffusion Coefficient of Methane in Nanoporous Materials

2006

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“…Many studies have addressed the diffusion of gases in zeolites, finding a wide variety in diffusion behavior [8][9][10][11]. In many chemical engineering applications it is assumed that the corrected diffusion coefficient of particles in confinement is independent of loading [3,4,[12][13][14].…”

mentioning

confidence: 99%

“…In many chemical engineering applications it is assumed that the corrected diffusion coefficient of particles in confinement is independent of loading [3,4,[12][13][14]. In an elaborate study, comparing the diffusion of four gases in four zeolite topologies, Skoulidas and Sholl confirmed the validity of this assumption (the so-called Darken assumption) for one system only: CH 4 in MFI; in other systems it was refuted, but a general rationale for these phenomena was not discovered [5,11]. Despite the importance for many applications, conventional methods cannot explain when and why, for a given system, the diffusion will increase, decrease, or remain constant as a function of loading.…”

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confidence: 99%

Molecular Understanding of Diffusion in Confinement

2005

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We introduce a computational method to directly relate diffusivities to the microscopic behavior of the adsorbed molecules. We apply this method to gases in an MFI-type molecular sieve, the reference system in this field. Transitions in the number and nature of adsorption sites result in temporary local increases in the diffusion. This occurs at different loadings in each of the x, y, and z directions, giving rise to the complex loading behavior found experimentally. Our method can be applied to any adsorbent-adsorbate system, and provides a fundamental understanding of diffusion in confinement on a molecular level.

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Modeling of Transport and Accessibility in Zeolites

Calero¹

2010

Zeolites and Catalysis

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IntroductionModeling plays an important role in the field of zeolites and related porous materials. The use of molecular simulations allows the prediction of adsorption and diffusion coefficients in these materials and also provides important information about the processes taking place inside the porous structures at the molecular level [1-10]. Hence, molecular modeling is a very good complement to experimental work in the understanding of the molecular behavior inside the pores.Despite the great interest and the applicability of zeolites, there are still many facets of the molecular mechanisms for a given reaction inside their pores that are poorly understood. These mechanisms are important for (i) the way the zeolite adsorbs, diffuses, and concentrates the adsorbates near the specific active sites; (ii) the interactions between the zeolite and the adsorbates and the effect on the electronic properties of the system; (iii) the chemical conversion at the active site; and (iv) the way the zeolite disperses the final product. Detailed knowledge on the molecular mechanisms involved will eventually lead to an increase in the reaction efficiency.This chapter focuses on molecular modeling of transport and accessibility in zeolites. It describes how simulations have contributed to a better understanding of these materials and provides a summary of the state of the art as well as of current challenges. The chapter is organized as follows. First, common models and potentials are briefly described. This is followed by a general overview on current simulation methods to compute adsorption, diffusion, free energies, surface areas, and pore volumes. The chapter continues with some examples on applications of molecular modeling to processes of interest from the industrial and environmental point of view. Finally, the chapter closes with a summary and some remarks on future challenges.

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Molecular Dynamics Simulations of Self-Diffusivities, Corrected Diffusivities, and Transport Diffusivities of Light Gases in Four Silica Zeolites To Assess Influences of Pore Shape and Connectivity

Cited by 184 publications

References 42 publications

Loading Dependence of the Diffusion Coefficient of Methane in Nanoporous Materials

Loading Dependence of the Diffusion Coefficient of Methane in Nanoporous Materials

Molecular Understanding of Diffusion in Confinement

Modeling of Transport and Accessibility in Zeolites

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