Center for Molecular Modeling - P. Beato

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

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

Private attachment

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

Private attachment

1-s2.0-S0021951717300842-main.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

Private attachment

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

The effects of methanol or dimethyl ether as methylating agent during zeolite catalysed benzene methylation

kristof — Tue, 14 Apr 2015 13:30:09 +0000

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

ISBN/ISSN:

Talk

Conference / event / venue

12th European Congress on Catalysis (Europacat XII)

Kazan, Russia

Sunday, 30 August, 2015 to Friday, 4 September, 2015

Abstract (private)

EuropaCat2015_MartinezEspin_Abstract_V4 (3).pdf