Center for Molecular Modeling - S. Bailleul

Ab initio enhanced sampling kinetic study on MTO ethene methylation reaction

michel — Mon, 20 Apr 2020 11:56:04 +0000

S. Bailleul, K. Dedecker, P. Cnudde, L. Vanduyfhuys, M. Waroquier, V. Van Speybroeck

Journal of Catalysis

388, 38-51

2020

Abstract

The methylation reaction of ethene with methanol over the Brønsted acidic ZSM-5 catalyst is one of theprototype reactions within zeolite catalysis for which experimental kinetic data is available. It is one ofthe premier reactions within the methanol-to-olefins process and has been the subject of extensive the-oretical testing to predict the reaction rates. Herein, we apply, for the first time, first principle moleculardynamics methods to determine the intrinsic reaction kinetics taking into account the full configurationalentropy. As chemical reactions are rare events, enhanced sampling methods are necessary to obtain suf-ficient sampling of the configurational space at the activated region. A plethora of methods is availablewhich depend on specific choices like the selection of collective variables along which the dynamics isenhanced. Herein, a thorough first principle molecular dynamics study is presented to determine thereaction kinetics via various enhanced MD techniques on an exemplary reaction within zeolite catalysisfor which reference theoretical and experimental data are available.

Green Open Access

DOI

http://dx.doi.org/10.1016/j.jcat.2020.04.015

Private attachment

Bailleul JCAT 2020 kinetics.pdf

Bailleul JCAT 2020 kinetics ESI.pdf

A Supramolecular View on the Cooperative Role of Brønsted andLewis Acid Sites in Zeolites for Methanol Conversion

samuel — Wed, 11 Sep 2019 08:32:20 +0000

S. Bailleul, I. Yarulina, A.E.J. Hoffman, A. Dokania, E. Abou-Hamad, A. Dutta Chowdhury, G. Pieters, J. Hajek, K. De Wispelaere, M. Waroquier, J. Gascon, V. Van Speybroeck

JACS (Journal of the American Chemical Society)

141 (37), 14823-14842

2019

Abstract

A systematic molecular level and spectroscopic investigation is presented to show the cooperative role of Brønsted acid and Lewis acid sites in zeolites for the conversion of methanol. Extra-framework alkaline-earth metal containing species and aluminum species decrease the number of Brønsted acid sites, as protonated metal clusters are formed. A combined experimental and theoretical effort shows that postsynthetically modified ZSM-5 zeolites, by incorporation of extra-framework alkaline-earth metals or by demetalation with dealuminating agents, contain both mononuclear [MOH]+ and double protonated binuclear metal clusters [M(μ-OH)2M]2+ (M = Mg, Ca, Sr, Ba, and HOAl). The metal in the extra-framework clusters has a Lewis acid character, which is confirmed experimentally and theoretically by IR spectra of adsorbed pyridine. The strength of the Lewis acid sites (Mg > Ca > Sr > Ba) was characterized by a blue shift of characteristic IR peaks, thus offering a tool to sample Lewis acidity experimentally. The incorporation of extra-framework Lewis acid sites has a substantial influence on the reactivity of propene and benzene methylations. Alkaline-earth Lewis acid sites yield increased benzene methylation barriers and destabilization of typical aromatic intermediates, whereas propene methylation routes are less affected. The effect on the catalytic function is especially induced by the double protonated binuclear species. Overall, the extra-framework metal clusters have a dual effect on the catalytic function. By reducing the number of Brønsted acid sites and suppressing typical catalytic reactions in which aromatics are involved, an optimal propene selectivity and increased lifetime for methanol conversion over zeolites is obtained. The combined experimental and theoretical approach gives a unique insight into the nature of the supramolecular zeolite catalyst for methanol conversion which can be meticulously tuned by subtle interplay of Brønsted and Lewis acid sites.

Open Access version available at UGent repository

Gold Open Access

DOI

https://doi.org/10.1021/jacs.9b07484

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jacs.9b07484.pdf

Insight into the role of water on the methylation of hexamethylbenzene in H-SAPO-34 from first principle molecular dynamics simulations

sven — Thu, 13 Jun 2019 10:11:51 +0000

S. Bailleul, S.M.J. Rogge, L. Vanduyfhuys, V. Van Speybroeck

ChemCatChem

11 (16), 3993-4010

2019

Abstract

The methylation of hexamethylbenzene with methanol is one of the key reactions in the methanol‐to‐olefins hydrocarbon pool reaction cycle taking place over the industrially relevant H‐SAPO‐34 zeolite. This methylation reaction can occur either via a concerted or via a stepwise mechanism, the latter being the preferred pathway at higher temperatures. Herein, we systematically investigate how a complex reaction environment with additional water molecules and higher concentrations of Brønsted acid sites in the zeolite impacts the reaction mechanism. To this end, first principle molecular dynamics simulations are performed using enhanced sampling methods to characterize the reactants and products in the catalyst pores and to construct the free energy profiles. The most prominent effect of the dynamic sampling of the reaction path is the stabilization of the product region where water is formed, which can either move freely in the pores of the zeolite or be stabilized through hydrogen bonding with the other protic molecules. These protic molecules also stabilize the deprotonated Brønsted acid site, created due to the formation of the heptamethylbenzenium cation, via a Grotthuss‐type mechanism. Our results provide fundamental insight in the experimental parameters that impact the methylation of hexamethylbenzene in H‐SAPO‐34, especially highlighting and rationalizing the crucial role of water in one of the main reactions of the aromatics‐based reaction cycle.

Gold Open Access

DOI

http://dx.doi.org/10.1002/cctc.201900618

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cctc.201900618.pdf

Structure–performance descriptors and the role of Lewis acidity in the methanol-to-propylene process

wim — Tue, 26 Jun 2018 06:37:22 +0000

I. Yarulina, K. De Wispelaere, S. Bailleul, J. Goetze, M. Radersma, E. Abou-Hamad, I. Vollmer, M. Goesten, B. Mezari, E.J.M. Hensen, J. S. Martínez-Espín, M. Morten, S. Mitchell, J. Perez-Ramirez, U. Olsbye, B.M. Weckhuysen, V. Van Speybroeck, F. Kapteijn, J. Gascon

Nature Chemistry

10 (8), 804-812

2018

Abstract

The combination of well-defined acid sites, shape-selective properties and outstanding stability places zeolites among the most practically relevant heterogeneous catalysts. The development of structure–performance descriptors for processes that they catalyse has been a matter of intense debate, both in industry and academia, and the direct conversion of methanol to olefins is a prototypical system in which various catalytic functions contribute to the overall performance. Propylene selectivity and resistance to coking are the two most important parameters in developing new methanol-to-olefin catalysts. Here, we present a systematic investigation on the effect of acidity on the performance of the zeolite ‘ZSM-5’ for the production of propylene. Our results demonstrate that the isolation of Brønsted acid sites is key to the selective formation of propylene. Also, the introduction of Lewis acid sites prevents the formation of coke, hence drastically increasing catalyst lifetime.

DOI

http://dx.doi.org/10.1038/s41557-018-0081-0

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s41557-018-0081-0.pdf

Suppression of the Aromatic Cycle in Methanol-to-Olefins Reaction over ZSM-5 by Post-Synthetic Modification Using Calcium

kristof — Fri, 15 Jan 2016 15:18:56 +0000

I. Yarulina, S. Bailleul, A. Pustovarenko, J. Ruiz-Martinez, K. De Wispelaere, J. Hajek, B.M. Weckhuysen, K. Houben, M. Baldus, V. Van Speybroeck, F. Kapteijn, J. Gascon

ChemCatChem

8 (19) 3057–3063

2016

Abstract

Incorporation of Ca in ZSM-5 results in a twofold increase of propylene selectivity (53 %), a total light-olefin selectivity of 90 %, and a nine times longer catalyst lifetime (throughput 792 gMeOH gcatalyst−1) in the methanol-to-olefins (MTO) reaction. Analysis of the product distribution and theoretical calculations reveal that post-synthetic modification with Ca2+ leads to the formation of CaOCaOH+ that strongly weaken the acid strength of the zeolite. As a result, the rate of hydride transfer and oligomerization reactions on these sites is greatly reduced, resulting in the suppression of the aromatic cycle. Our results further highlight the importance of acid strength on product selectivity and zeolite lifetime in MTO chemistry.

DOI

http://dx.doi.org/10.1002/cctc.201600650

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Yarulina_et_al-2016-ChemCatChem.pdf

Towards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditions

kristof — Mon, 30 Nov 2015 15:08:34 +0000

K. De Wispelaere, S. Bailleul, V. Van Speybroeck

Catalysis Science & Technology

6, 2686 – 2705

2016

Abstract

Zeolites are the workhorses of today’s chemical industry. For decades they have been successfully applied, however many features of zeolite catalysis are only superficially understood and in particular the kinetics and mechanism of individual reaction steps at operating conditions. Herein we use state-of-the-art advanced ab initio molecular dynamics techniques to study the influence of catalyst topology and acidity, reaction temperature and the presence of additional guest molecules on elementary reactions. Such advanced modeling techniques provide complementary insight to experimental knowledge as the impact of individual factors on the reaction mechanism and kinetics of zeolite-catalyzed reactions may be unraveled. We study key reaction steps in the conversion of methanol to hydrocarbons, namely benzene and propene methylation. These reactions may occur either in a concerted or stepwise fashion, i.e. methanol directly transfers its methyl group to a hydrocarbon or the reaction goes through a framework-bound methoxide intermediate. The DFT-based dynamical approach enables mimicking reaction conditions as close as possible and studying the competition between two methylation mechanisms in an integrated fashion. The reactions are studied in the unidirectional AFI-structured H-SSZ-24, H-SAPO-5 and TON-structured H-ZSM-22 materials. We show that varying the temperature, topology, acidity and number of protic molecules surrounding the active site may tune the reaction mechanism at the molecular level. Obtaining molecular control is crucial in optimizing current zeolite processes and designing emerging new technologies bearing alternative feedstocks.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1039/C5CY02073E

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c5cy02073e.pdf

Influence of topology, nature of the active site and operating conditions on the formation and growth of aromatics in zeolites

samuel — Tue, 14 Jan 2020 15:20:57 +0000

D. De Saegher

Master of Science in Chemical Engineering

2019

Supervisors

Prof. Dr. ir. Veronique Van Speybroeck, dr. Kristof De Wispelaere

Operando First Principle Simulations of Important Chemical Transformations over Zeolites within the Methanol-to-Olefin Process

samuel — Tue, 14 Jan 2020 10:39:34 +0000

S. Bailleul

Wed, 18/12/2019

Faculty of Engineering and Architecture, Jozef Plateaustraat, Ghent

https://biblio.ugent.be/publication/8642766

Supervisors

Prof. Dr. ir. Veronique Van Speybroeck

Attachment (private)

PhD_Simon_Bailleul_compressed.pdf

Enhanced sampling study of the temperature influence on the methylation of ethene in H-ZSM-5

cnudde — Tue, 10 Jul 2018 09:33:34 +0000

Period

Sunday, 15 July, 2018 to Friday, 15 March, 2019

Node days

3 360.00 days

Users

S. Bailleul, P. Cnudde

Remaining days

2 150.00 days

TIER1 reference n°

2018-43

Status

Approved

Modeling the influence of zeolite acidity on MTO methylation reactions

cnudde — Thu, 08 Mar 2018 09:30:10 +0000

Period

Monday, 5 March, 2018 to Monday, 5 November, 2018

Node days

4 960.00 days

Users

P. Cnudde, S. Bailleul, K. De Wispelaere

Remaining days

0.00 days

TIER1 reference n°

2018-12

Status

Approved