Center for Molecular Modeling - G. Sastre

Light Olefin Diffusion during the MTO Process on H-SAPO-34: a Complex Interplay of Molecular Factors

cnudde — Sun, 15 Mar 2020 16:53:30 +0000

P. Cnudde, R. Demuynck, S. Vandenbrande, M. Waroquier, G. Sastre, V. Van Speybroeck

JACS (Journal of the American Chemical Society)

142 (13), 6007-6017

2020

Abstract

The methanol-to-olefins process over H-SAPO-34 is characterized by its high shape selectivity toward light olefins. The catalyst is a supramolecular system consisting of nanometer-sized inorganic cages, decorated by Brønsted acid sites, in which organic compounds, mostly methylated benzene species, are trapped. These hydrocarbon pool species are essential to catalyze the methanol conversion but may also clog the pores. As such, diffusion of ethene and propene plays an essential role in determining the ultimate product selectivity. Enhanced sampling molecular dynamics simulations based on either force fields or density functional theory are used to determine how molecular factors influence the diffusion of light olefins through the 8-ring windows of H-SAPO-34. Our simulations show that diffusion through the 8-ring in general is a hindered process, corresponding to a hopping event of the diffusing molecule between neighboring cages. The loading of different methanol, alkene, and aromatic species in the cages may substantially slow down or facilitate the diffusion process. The presence of Brønsted acid sites in the 8-ring enhances the diffusion process due to the formation of a favorable π-complex host–guest interaction. Aromatic hydrocarbon pool species severely hinder the diffusion and their spatial distribution in the zeolite crystal may have a significant effect on the product selectivity. Herein, we unveil how molecular factors influence the diffusion of light olefins in a complex environment with confined hydrocarbon pool species, high olefin loadings, and the presence of acid sites by means of enhanced molecular dynamics simulations under operating conditions.

DOI

http://dx.doi.org/10.1021/jacs.9b10249

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Cnudde_Diffusion_JACS.pdf

Vibrational fingerprint of the absorption properties of UiO-type MOF materials

andy — Wed, 16 Sep 2015 12:38:04 +0000

A. Van Yperen-De Deyne, K. Hendrickx, L. Vanduyfhuys, G. Sastre, P. Van der Voort, V. Van Speybroeck, K. Hemelsoet

Theoretical Chemistry Accounts

135, 4, 102

2016

Abstract

The absorption properties of UiO-type metal–organic frameworks are computed using TD-DFT simulations on the organic linkers. A set of nine isoreticular structures, including the UiO-66 and UiO-67 materials and functionalized variants, are examined. The excitation energies from a static geometry optimization are compared with dynamic averages obtained from sampling the ground-state potential energy surface using molecular dynamics. The vibrational modes that impact the excitation energy are identified. This analysis is done using a recently proposed tool based on power spectra of the velocities and the excitation energies. The applied procedure allows including important factors influencing the absorption spectra, such as the periodic framework, linker variation and dynamical effects including harmonic and anharmonic nuclear motions. This methodology allows investigating in detail the vibrational fingerprint of the excitation energy of advanced materials such as MOFs and gives perspectives to tailor materials toward new light-based applications.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1007/s00214-016-1842-8

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16-TheorChemAcc-135-102-VanYperenDeDeyne.pdf

Shape-selective diffusion of olefins in 8-ring solid acid microporous zeolites

michel — Fri, 19 Jun 2015 20:01:35 +0000

A. Ghysels, S.L. Moors, K. Hemelsoet, K. De Wispelaere, M. Waroquier, G. Sastre, V. Van Speybroeck

Journal of Physical Chemistry C

119, 41, 23721-23734

2015

Abstract

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.

Open Access version available at UGent repository

Green Open Access

DOI

http://dx.doi.org/10.1021/acs.jpcc.5b06010

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15-JPhysChemC-xxxx-Ghysels.pdf

acs%2Ejpcc%2E5b06010.pdf

Correction to “Shape-Selective Diffusion of Olefins in 8-Ring Solid Acid Microporous Zeolites”

wim — Mon, 05 Feb 2018 12:12:12 +0000

A. Ghysels, S.L. Moors, K. Hemelsoet, K. De Wispelaere, M. Waroquier, G. Sastre, V. Van Speybroeck

JOURNAL OF PHYSICAL CHEMISTRY C

2017

pubs.acs.org

Selective diffusion of small hydrocarbons in acidic zeolites with 8-rings

kristof — Mon, 12 Jan 2015 09:24:57 +0000

A. Ghysels, S.L. Moors, K. Hemelsoet, K. De Wispelaere, G. Sastre, V. Van Speybroeck

ISBN/ISSN:

Poster

Conference / event / venue

2nd Euro-Asia Zeolite Conference

Nice, France

Sunday, 25 January, 2015 to Wednesday, 28 January, 2015

Abstract (private)

Abstract Euro-Asian Conference 2015 -VeroniqueVanSpeybroeck.pdf

Molecular dynamics study of shape-selective diffusion in 8-ring acidic zeolites

wim — Wed, 15 Oct 2014 06:40:41 +0000

A. Ghysels, S.L. Moors, K. Hemelsoet, K. De Wispelaere, G. Sastre, V. Van Speybroeck

ISBN/ISSN:

Talk

Conference / event / venue

WATOC 2014 Satellite Meeting on Large Condensed and Biological Systems

Concepción, Chili

Monday, 13 October, 2014 to Tuesday, 14 October, 2014

Conference reference

WATOC 2014 Satellite Meeting on Large Condensed and Biological Systems

Selective diffusion of small hydrocarbons through acidic zeolites with 8- membered rings

wim — Mon, 13 Oct 2014 07:11:59 +0000

A. Ghysels, S.L. Moors, K. Hemelsoet, K. De Wispelaere, G. Sastre, V. Van Speybroeck

ISBN/ISSN:

Poster

Conference / event / venue

WATOC 2014

Santiago de Chile, Chile

Sunday, 5 October, 2014 to Friday, 10 October, 2014

Abstract (private)

2014_WATOC2014_AG_sapos.pdf

Conference reference

WATOC 2014

Molecular dynamics study of shape-selective diffusion in 8-ring acidic zeolites

sam — Mon, 29 Sep 2014 15:03:10 +0000

S.L. Moors, A. Ghysels, K. De Wispelaere, G. Sastre, K. Hemelsoet, M. Waroquier, V. Van Speybroeck

105

ISBN/ISSN:

Talk

Conference / event / venue

6 th FEZA Conference 2014

Leipzig, Germany

Monday, 8 September, 2014 to Thursday, 11 September, 2014

Abstract (private)

abstract_s_moors.pdf

Conference reference

FEZA 2014