A molecular dynamics investigation of the diffusion characteristics of cavity-type zeolites with 8-ring windows

Krishna, Rajamani; Baten, J.M. van

doi:10.1016/j.micromeso.2010.08.026

Cited by 93 publications

(131 citation statements)

References 54 publications

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“…Krishna et al used this approach to study methane diffusion in several 8-ring 5 zeolites. 34,46 They found very similar diffusion coefficients for the simulations with a rigid and flexible zeolite, summarized the link between ring diameter and diffusion coefficient, and confirmed an exponential trend. Awati et al 33 investigated the ring diameter distribution in great detail, more specifically ring anharmonicity and ring shape (circular versus elliptical, framed 'dimensionality' in Ref.…”

mentioning

confidence: 82%

“…This explicit derivation of diffusivities has been extensively studied in literature, e.g. by Awati et al 33 , Krishna et al 34 , Smit and Maessen et al 26 , Garcia and Dubbeldam et al 35 , O'Malley et al 32 , Kiel et al [36][37][38][39] in various materials, for various hydrocarbons. For processes where diffusion barriers are too high, MD runs may be too slow to efficiently generate particle trajectories over the time-scale of the diffusion process.…”

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confidence: 98%

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Shape-Selective Diffusion of Olefins in 8-Ring Solid Acid Microporous Zeolites

et al. 2015

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The diffusion of olefins through 8-ring solid acid microporous zeolites is investigated using molecular dynamics simulations techniques and using a newly developed flexible force field. Within the context of the Methanol to Olefin (MTO) process and the observed product distribution, knowledge on the diffusion paths is essential to obtain molecular level control over the process conditions. Eight-ring zeotype materials are favorably used for the MTO process as they give a selective product distribution towards low carbon olefins. To investigate how composition, acidity and flexibility influence the diffusion paths of ethene and propene, a series of isostructural aluminosilicates (zeolites) and silicoaluminophosphates (AlPOs and SAPOs) are investigated with and without randomly distributed acidic sites. Distinct variations in diffusion of ethene are observed in terms of temperature, composition, acidity, and topology (AEI, CHA, AFX). In general, diffusion of ethene is an activated process for which free energy barriers for individual rings may be determined. We observe ring dependent diffusion behavior which can not solely be described in terms of the composition and topology of the rings. A new descriptor had to be introduced namely the accessible window area (AWA), inspired by implicit solvation models of proteins and small molecules. The AWA may be determined throughout the molecular dynamics trajectories and correlates well with the number of ring crossings at the molecular level and the free energy barriers for ring crossings from one cage to the other. The overall observed diffusivity is determined by molecular characteristics of individual rings for which AWA is a proper descriptor. Temperature-induced changes in framework dynamics and diffusivity may be captured by following the new descriptor throughout the simulations.

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confidence: 82%

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confidence: 98%

Shape-Selective Diffusion of Olefins in 8-Ring Solid Acid Microporous Zeolites

et al. 2015

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“…However, "static" effects, such as the average window size, have been proven to be very crucial to transport in zeolites. [12][13][14][15] In this light, the modeling approach chosen again proves to be realistic enough for drawing valid "real-world" conclusions while being efficient for the demanding transient molecular dynamics simulations.…”

Section: Modelsmentioning

confidence: 99%

“…But most evidence points today at the fact that the influence is minor, particularly for rather small molecules such as methane. [12][13][14][15] Purely dynamic effects, such as the "breathing window", 10 do most likely not have any significant influence. The term refers to the idea that the window atoms of a zeolite structure move as soon as a guest molecule appears so that the window size increases and the passage of the guest molecule is considerably facilitated.…”

Section: Modelsmentioning

confidence: 99%

Transport into Nanosheets: Diffusion Equations Put to Test

2013

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Ultrathin porous materials, such as zeolite nanosheets, are prominent candidates for performing catalysis, drug supply, and separation processes in a highly efficient manner due to exceptionally short transport paths. Predictive design of such processes requires the application of diffusion equations that were derived for macroscopic, homogeneous surroundings to nanoscale, nanostructured host systems. Therefore, we tested different analytical solutions of Fick’s diffusion equations for their applicability to methane transport into two different zeolite nanosheets (AFI, LTA) under instationary conditions. Transient molecular dynamics simulations provided hereby concentration profiles and uptake curves to which the different solutions were fitted. Two central conclusions were deduced by comparing the fitted transport coefficients. First, the transport can be described correctly only if concentration profiles are used and the transport through the solid–gas interface is explicitly accounted for by the surface permeability. Second and most importantly, we have unraveled a size limitation to applying the diffusion equations to nanoscale objects. This is because transport-diffusion coefficients, D T, and surface permeabilities, α, of methane in AFI become dependent on nanosheet thickness. Deviations can amount to factors of 2.9 and 1.4 for D T and α, respectively, when, in the worst case, results from the thinnest AFI nanosheet are compared with data from the thickest sheet. We present a molecular explanation of the size limitation that is based on memory effects of entering molecules and therefore only observable for smooth pores such as AFI and carbon nanotubes. Hence, our work provides important tools to accurately predict and intuitively understand transport of guest molecules into porous host structures, a fact that will become the more valuable the more tiny nanotechnological objects get.

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“…147 Los procesos de separación basados en zeolitas intercambiadas se llevan a cabo a través de la formación de complejos de tipo π, los cuales se forman cuando iones de Cu o Ag, previamente adicionados a la estructura zeolíti-ca, interaccionan con las moléculas insaturadas, 148,149 mientras que en el caso de separaciones que involucran zeolitas puramente silíceas la separación se da por efectos de tamizado molecular. 20,21,141,150 En este capítulo se estudia la dinámica de la red cristalina y las consecuencias que el modelamiento de la flexibilidad de dicha red tendrá sobre la movilidad de las especies adsorbidas. Para este fin usaremos la técnica de Dinámica Molecular…”

Section: Términos No-enlazantesunclassified

Difusión Selectiva de Hidrocarburos en Zeolitas de Poro Pequeño a Partir de Técnicas de Simulación Molecular

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A Germán Sastre, director de mi tesis, por su incondicional apoyo y por su excepcional trabajo como tutor de mi trabajo doctoral.A Avelino Corma, por darme la oportunidad de trabajar en el ITQ, y por ser una fuente inagotable de inspiración.A Amparo Mifsud, por su ayuda y disposición, y por hacer del ITQ un lugar mucho mas amable.A Jaime Primo, un agradecimiento especial por su paciencia y por sus consejos.A Mónica, Inma y Marcos: su trabajo es altamente apreciado, su colaboración, sin duda alguna, hace mas fácil el camino.A José Sanchez Marín, profesor de la Universidad de Valencia, por su diligencia y colaboración.Un agradecimiento especial a Diego Gómez, por las muchas y fructíferas conversaciones sobre ciencia y computadores, pero sobre todo por ser un excelente compañero.A Siris, Peter, Angeles, Mer, Tirso, Adela por hacer del laboratorio un lugar de trabajo muy agradable.A Peter Vennestrøm una mención especial por su colaboración por hacer que el primer contacto que un grupo muy especial de niños tuvo con la ciencia fuera tan divertido y seguramente inolvidable.The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' but 'That's funny ...' Isaac Asimov II Un agradecimiento muy especial a Yuriy Bushuev, por las enriquecedoras conversaciones que tuvimos mientras estuvo en el ITQ, y las que sin ninguna duda se darán en el futuro.Mis agradecimientos no estarían completos si no incluyeran a la persona que me abrió las puertas de la química teórica y computacional, a Scott M. Auerbach, por mostrarme el camino que seguramente seguiré recorriendo en el futuro.

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A molecular dynamics investigation of the diffusion characteristics of cavity-type zeolites with 8-ring windows

Cited by 93 publications

References 54 publications

Shape-Selective Diffusion of Olefins in 8-Ring Solid Acid Microporous Zeolites

Shape-Selective Diffusion of Olefins in 8-Ring Solid Acid Microporous Zeolites

Transport into Nanosheets: Diffusion Equations Put to Test

Difusión Selectiva de Hidrocarburos en Zeolitas de Poro Pequeño a Partir de Técnicas de Simulación Molecular

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