Center for Molecular Modeling - S. Svelle

Acidity effect on benzene methylation kinetics over substituted H-MeAlPO-5 catalysts

cnudde — Mon, 24 Jan 2022 08:51:50 +0000

M. Morten, T. Cordero-Lanzac, P. Cnudde, E. A. Redekop, S. Svelle, V. Van Speybroeck, U. Olsbye

Journal of Catalysis

404, 594-606

2021

Abstract

Methylation of aromatic compounds is a key reaction step in various industrial processes such as the aromatic cycle of methanol-to-hydrocarbons chemistry. The study of isolated methylation reactions and of the influence of catalyst acidity on their kinetics is a challenging task. Herein, we have studied unidirectional metal-substituted H-MeAlPO-5 materials to evaluate the effect of acid strength on the kinetics of benzene methylation with DME. First-principle simulations showed a direct correlation between the methylation barrier and acid site strength, which depends on the metal substituent. Three H-MeAlPO-5 catalysts with high (Me = Mg), moderate (Me = Si) and low acidity (Me = Zr) were experimentally tested, confirming a linear relationship between the methylation activation energy and acid strength. The effects of temperature and reactant partial pressure were evaluated, showing significant differences in the byproduct distribution between H-MgAlPO-5 and H-SAPO-5. Comparison with propene methylation suggested that the Mg substituted catalyst is also the most active for the selective methylation of alkenes.

Open Access version available at UGent repository

Gold Open Access

DOI

http://dx.doi.org/10.1016/j.jcat.2021.11.002

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1-s2.0-S0021951721004619-main (1).pdf

Collective action of water molecules in zeolite dealumination

kristof — Tue, 26 Mar 2019 14:48:15 +0000

M. Nielsen, A. Hafreager, R. Brogaard, K. De Wispelaere, H. Falsig, P. Beato, V. Van Speybroeck, S. Svelle

Catalysis Science & Technology

9 (14), 3721-3725

2019

Abstract

When exposed to steam, zeolite catalysts are irreversibly deactivated by loss of acidity and framework degradation caused by dealumination. Steaming typically occurs at elevated temperatures, making it challenging to investigate the mechanism with most approaches. Herein, we follow the dynamics of zeolite dealumination in situ, in the presence of a realistic loading of water molecules by means of enhanced sampling molecular dynamics simulations. H-SSZ-13 zeolite is chosen as a target system. Monte Carlo simulations predict a loading of more than 3 water molecules per unit cell at representative steaming conditions (450 °C, 1 bar steam). Our results show that a higher water loading lowers the free energy barrier of dealumination, as water molecules cooperate to facilitate hydrolysis of Al–O bonds. We find free energies of activation for dealumination that agree well with the available experimental measurements. Clearly, the use of enhanced sampling molecular dynamics yields a major step forward in the molecular level understanding of the dealumination; insight which is very hard to derive experimentally.

Gold Open Access

DOI

http://dx.doi.org/10.1039/c9cy00624a

Understanding zeolite-catalyzed benzene methylation reactions by methanol and dimethyl ether at operating conditions from first principle microkinetic modeling and experiments

kristof — Tue, 28 Nov 2017 15:22:45 +0000

K. De Wispelaere, J. S. Martínez-Espín, M. J. Hoffmann, S. Svelle, U. Olsbye, T. Bligaard

Catalysis Today

312, 35-43

2018

Abstract

In methanol-to-hydrocarbon chemistry, methanol and dimethyl ether (DME) can act as methylating agents. Therefore, we focus on the different reactivity of methanol and DME towards benzene methylation in H-ZSM-5 at operating conditions by combining first principles microkinetic modeling and experiments. Methylation reactions are known to follow either a concerted reaction path or a stepwise mechanism going through a framework-bound methoxide. By constructing a DFT based microkinetic model including the concerted and stepwise reactions, product formation rates can be calculated at conditions that closely mimic the experimentally applied conditions. Trends in measured rates are relatively well reproduced by our DFT based microkinetic model. We find that benzene methylation with DME is faster than with methanol but the difference decreases with increasing temperature. At low temperatures, the concerted mechanism dominates, however at higher temperatures and low pressures the mechanism shifts to the stepwise pathway. This transition occurs at lower temperatures for methanol than for DME, resulting in smaller reactivity differences between methanol and DME at high temperature. Our theory-experiment approach shows that the widely assumed rate law with zeroth and first order in oxygenate and hydrocarbon partial pressure is not generally applicable and depends on the applied temperature, pressure and feed composition.

DOI

http://dx.doi.org/10.1016/j.cattod.2018.02.042

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1-s2.0-S0920586118301159-main.pdf

Hydrogen transfer versus methylation: on the genesis of aromatics formation in the Methanol-To-Hydrocarbons over H-ZSM-5

kristof — Fri, 19 May 2017 22:58:55 +0000

J. S. Martínez-Espín, K. De Wispelaere, T. V. Janssens, S. Svelle, K. P. Lillerud, P. Beato, V. Van Speybroeck, U. Olsbye

ACS Catalysis

7, 5773–5780

2017

Abstract

The catalytic conversion of methanol (MeOH) and dimethyl ether (DME) into fuels and chemicals over zeolites (MTH process) is industrially emerging as an alternative route to conventional oil-derived processes. After 40 years of research, a detailed mechanistic understanding of the intricate reaction network is still not fully accomplished. The overall reaction is described as two competitive catalytic cycles, dominated by alkenes and arenes, which are methylated and cracked or dealkylated to form effluent products. Herein, we present the reaction of isobutene with methanol and DME as an efficient tool for measuring the relative formation rates of alkenes and arenes, and we provide detailed mechanistic insight into the hydrogen-transfer reaction. We provide experimental and theoretical evidence that manifest a strong competition of methylation and hydrogen transfer of isobutene by methanol, while methylation is substantially favored by DME. Experiments performed at higher conversion facilitate projection of the results to the product distribution obtained when using MeOH or DME as feedstock during the MTH reaction.

DOI

http://dx.doi.org/10.1021/acscatal.7b01643

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acscatal.7b01643.pdf

Benzene co-reaction with methanol and dimethyl ether over zeolite and zeotype catalysts: Evidence of parallel reaction paths to toluene and diphenylmethane

kristof — Sun, 18 Sep 2016 19:16:42 +0000

J. S. Martínez-Espín, K. De Wispelaere, M. Westgård Erichsen, S. Svelle, T. V. Janssens, V. Van Speybroeck, P. Beato, U. Olsbye

Journal of Catalysis

349, 136-148

2017

Abstract

The reactivity of methanol (MeOH) and dimethyl ether (DME) toward benzene was studied over zeolitic materials with different topology and acid strength (H-ZSM-5, H-SSZ-24, and H-SAPO-5) at 250–350 °C. Higher rates of methylation, and subsequent de-alkylation reactions, were observed with DME compared to MeOH. In addition, significant differences in product distribution based on the choice of methylating agent were observed. For reactions between MeOH and benzene a fraction of diphenylmethanes (DPMs) was formed, while this product group was nearly absent during reactions between DME and benzene. A range of co-feed and isotopic labeling experiments was performed, mainly over H-ZSM-5, in order to elucidate mechanistic information on the pathway from methanol and benzene to DPMs. Overall, these studies revealed that DPM formation involves the dehydrogenation of methanol to formaldehyde on the Brønsted acid site, followed by subsequent reaction with two benzene molecules. Theoretical calculations confirmed the higher reactivity of DME compared to MeOH toward benzene methylation and suggested a plausible route from formaldehyde and benzene to DPM.

Open Access version available at UGent repository

Green Open Access

DOI

http://dx.doi.org/10.1016/j.jcat.2017.03.007

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1-s2.0-S0021951717300842-main.pdf

How zeolitic acid strength and composition alter the reactivity of alkenes and aromatics towards methanol

michel — Wed, 10 Sep 2014 11:53:49 +0000

M.W. Erichsen, K. De Wispelaere, K. Hemelsoet, S.L. Moors, T. Deconinck, M. Waroquier, S. Svelle, V. Van Speybroeck, U. Olsbye

Journal of Catalysis

328, 186-196

2015

Abstract

This work encompasses a combined experimental and theoretical assessment of how zeolitic acid strength and composition affects acid-catalysed methylation reactions. Overall, higher methylation rates were observed over the material with higher acid strength. Co-reactions of methanol with benzene at 250 degrees C over the two isostructural AFI materials H-SSZ-24 and H-SAPO-5 revealed large differences in selectivity. While the stronger acidic H-SSZ-24 mainly produced toluene and polymethylbenzenes, high yields of C4+ aliphatics were observed over H-SAPO-5. These results strongly suggest that alkene methylation was preferred over H-SAPO-5 even at very low conversion during methanol/benzene co-reactions. Furthermore, a comparison of benzene and propene methylation at 350-400 degrees C revealed a significantly faster rate of benzene than propene methylation in H-SSZ-24, whereas the rates of benzene and propene methylation were similar in H-SAPO-5. The observed difference in reactivity of the two hydrocarbons in both catalysts could be understood by careful analysis of various molecular dynamics simulations of the co-adsorbed complexes. The probability to form protonated methanol was, as expected, higher in the more acidic material. However, in H-SSZ-24, the probability for methanol protonation was higher when co-adsorbed with benzene than when co-adsorbed with propene, while the same was not observed in H-SAPO-5. Furthermore, it was found that benzene and methanol are more likely to form a reactive co-adsorbed complex in H-SSZ-24 compared to propene and methanol, while the opposite was observed for H-SAPO-5. This work shows that molecular dynamics simulations provide insights into the adsorption behaviour of guest molecules in large pore AFI materials. The obtained insights correlate with the experimentally observed reactivities. (C) 2015 Elsevier Inc. All rights reserved.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1016/j.jcat.2015.01.013

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15_JCatalysis_328,186_Erichsen.pdf

Methylation of benzene by methanol: single-site kinetics over H-ZSM-5 and H-beta zeolite catalysts

jeroen — Wed, 29 Feb 2012 08:51:13 +0000

J. Van der Mynsbrugge, M. Visur, U. Olsbye, P. Beato, M. Bjørgen, V. Van Speybroeck, S. Svelle

Journal of Catalysis

292, 201-212

2012

Abstract

Benzenemethylation by methanol is studied on acidic zeolitesH-ZSM-5 (MFI) and H-beta (BEA) to investigate the influence of the catalyst topology on the reaction rate. Experimental kinetic measurements at 350 °C using extremely high feed rates to suppress side reactions show that methylation occurs considerably faster on H-ZSM-5 than on H-beta. Theoretical rate constants, obtained from first-principles simulations on extended zeolite clusters, reproduce a higher methylation rate on H-ZSM-5 and provide additional insight into the various molecular effects that contribute to the overall differences between the two catalysts. The calculations indicate this higher methylation rate is primarily due to an optimal confinement of the reacting species in the medium pore material. Co-adsorption of methanol and benzene is energetically favored in H-ZSM-5 compared with H-beta, to the extent that the stabilizing host–guest interactions outweigh the greater entropy loss upon benzene adsorption in H-ZSM-5 vs. in H-beta.

Open Access version available at UGent repository

DOI

http://dx.doi.org/10.1016/j.jcat.2012.05.015

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12 j. of catalysis 292 201 Van der Mynsbrugge.pdf

single-site_kinetics_zsm5_beta_published_manuscript.pdf

Benzene co-reaction with methanol and dimethyl ether over zeolitic catalysts

kristof — Tue, 16 May 2017 21:04:21 +0000

J. S. Martínez-Espín, K. De Wispelaere, M. Westgård Erichsen, S. Svelle, T. V. Janssens, V. Van Speybroeck, P. Beato, U. Olsbye

ISBN/ISSN:

Talk

Conference / event / venue

25th North American Meeting of the Catalysis Society (NAM25)

Denver, CO, USA

Sunday, 4 June, 2017 to Friday, 9 June, 2017

On the Formation and Special Role of Formaldehyde in the Conversion of Methanol into Hydrocarbons

kristof — Wed, 01 Mar 2017 22:53:44 +0000

K. De Wispelaere, J. S. Martínez-Espín, S. Svelle, P. Beato, U. Olsbye, V. Van Speybroeck

ISBN/ISSN:

Talk

Conference / event / venue

25th North American Meeting of the Catalysis Society (NAM25)

Denver, CO, USA

Sunday, 4 June, 2017 to Friday, 9 June, 2017

Combined Theoretical and Experimental Study on the Influence of Zeolitic Acid Strength on the Methanol Conversion Process

kristof — Mon, 26 Oct 2015 15:40:02 +0000

K. De Wispelaere, M. Westgård Erichsen, K. Hemelsoet, S.L. Moors, T. Deconinck, S. Svelle, M. Waroquier, U. Olsbye, V. Van Speybroeck

ISBN/ISSN:

Poster

Conference / event / venue

IAP Annual Meeting

Hasselt, Belgium

Friday, 11 September, 2015