Center for Molecular Modeling - W. Chen (Wei - CMM)

Dynamic Evolution and Stability of Ketenes in MAPO-18 (M = Si or Mg): Molecular Insights into the Reaction Mechanism for CO2-to-Hydrocarbons

wei — Fri, 19 Dec 2025 21:01:12 +0000

W. Chen (Wei - CMM), M. Bocus, U. Olsbye, V. Van Speybroeck

Chinese Journal of Catalysis

2026

Abstract

AEI topology molecular sieves (MAPO-18) have shown promising properties as components of OX-ZEO type tandem catalysts, where the Brønsted acid sites (BAS) introduced by different framework substitutions lead to distinct catalytic mechanisms using ketene as key intermediates in the CO2-to-hydrocarbons conversion. This study provides molecular-level insights into the reactions of three ketenes (ketene, methyl ketene, and dimethyl ketene) with the BAS in MAPO-18 (M = Si, Mg) molecular sieves at operando conditions through firstprinciples molecular dynamics (FPMD) simulations combined with enhanced sampling techniques. Free energy surfaces constructed from FPMD simulations revealed distinct kinetic and thermodynamic preferences, linking them to different reaction routes for the production of olefins. Prior studies suggested that ketenes and their protonated analogues are key intermediates in two different pathways to olefins formation, and the three ketenes exhibited higher kinetic stability than their protonated forms in H-SAPO-18 compared to H-MgAPO-18, suggesting a high tendency for olefin production via the (cyclo)addition-decarboxylation route in H-SAPO-18. In contrast, the increased stability of the cationic intermediates and low protonation barrier for methyl and dimethyl ketenes in MgAPO-18 favor their direct decarbonylation to olefins. Surface-bound species displayed decreasing stability from surface acetate to surface propionate to surface isobutyrate, aligning with established trends for surface alkoxides. Moreover, a comparison with static calculations demonstrates their limited ability to capture the entropic contributions and dynamic effects that dominate the behavior of active intermediates under realistic reaction conditions, highlighting the necessity of MD approaches for accurate mechanistic modeling of catalytic reactions. Overall, this study provides key steps of ketene reactivity in zeolite frameworks, bridging computational and experimental insights into CO2-to-hydrocarbon conversion pathways. These results emphasize how subtle variations in the framework composition and substituents dictate the reaction mechanisms, offering guidance for the rational design of molecular sieves tailored for selective catalytic transformations.

DOI

http://dx.doi.org/

Understanding the entanglement between diffusion and reaction by probing the mobility of ketene in chabazites

wei — Fri, 12 Sep 2025 13:22:26 +0000

W. Chen (Wei - CMM), P. Cnudde, V. Van Speybroeck

Journal of Catalysis

453, 116546

2026

Abstract

In zeolite catalysis, diffusion and reaction are generally viewed as separate processes that independently affect catalytic performance due to the significant variation in timescales for diffusion and reaction. Nevertheless, this study reveals that reaction and diffusion can be intertwined, a phenomenon hitherto unexplored. In particular, we highlight this complex relationship for ketene intermediates in chabazite topologies, where the diffusion properties of ketene are notably affected by the reactivity with Brønsted acid sites (BAS) and guest molecules present in the zeolite pores. Ketene is an important intermediate in zeolite catalyzed methanol-to-hydrocarbons and COx-to-hydrocarbons conversion and its diffusion and reaction behavior directly impacts the catalytic performance. Our ab initio molecular dynamics simulations reveal that ketene diffusion is significantly facilitated by hydrogen bonding interactions with BAS during the diffusion through the 8-ring windows of chabazite, and that ketene can also readily react with other guest species along the diffusion pathway. This entanglement between reaction and diffusion can be attributed to the high activity of ketene, resulting in a strong competition between reaction and diffusion, which cannot be viewed as two independent processes. Therefore, our findings concerning the complex interconnection between diffusion and reaction not only contribute to the fundamental understanding of ketene chemistry in chabazite but also have important consequences for other fields of catalysis involving highly active intermediates.

DOI

http://dx.doi.org/10.1016/j.jcat.2025.116546

Formaldehyde-Mediated Initial Carbon–Carbon Bond Formation in Zeolite-Catalyzed Methanol-to-Hydrocarbon Conversion

wei — Wed, 18 Jun 2025 21:40:16 +0000

W. Chen (Wei - CMM), J. Sobalska, W. Fu, K. A. Tarach, M. Bocus, T. Tang, K. Góra-Marek, V. Van Speybroeck

JACS (Journal of the American Chemical Society)

147, 28, 24719–24733

2025

Abstract

Zeolite-catalyzed methanol-to-hydrocarbon conversion is a promising technology for the sustainable production of valuable hydrocarbon products. However, the mechanism behind the formation of the first carbon–carbon bond has been a subject of controversy for several decades. By comprehensive consideration of previous experimental phenomena and theoretical studies, a formaldehyde (HCHO)-based first carbon–carbon formation mechanism is proposed. Within the new mechanism, hydrated or methylated products of HCHO (methanediol, methyloxymethanol, and dimethyloxymethane) with much weaker C–H bond strengths replace methane in the traditional methane-HCHO mechanism, allowing energetically and kinetically favorable pathways to form the first C–C bond. The formed C–C bond products are further converted to ketene and olefins via the methylation-decarbonylation route. The plausibility of the newly proposed mechanism is confirmed by both theoretical calculations and experiments in various MTH zeolite catalysts. A key intermediate in this mechanism is glycolaldehyde, which was captured in situ by both mass spectrometry and Fourier transform infrared spectroscopy. The viability of the mechanism in different zeolites, as predicted theoretically, was also confirmed by gas chromatography. Not only does this new mechanism introduce an innovative pathway for the first C–C bond formation, but it also provides a comprehensive explanation of the specific role of HCHO in the early stage of the MTH process and associated reactions.

Open Access version available at UGent repository

Gold Open Access

DOI

http://dx.doi.org/10.1021/jacs.5c06141

Private attachment

formaldehyde-mediated-initial-carbon-carbon-bond-formation-in-zeolite-catalyzed-methan.pdf

Carbocation chemistry confined in zeolites: spectroscopic and theoretical characterizations

wei — Sat, 27 Jul 2024 03:44:09 +0000

W. Chen (Wei - CMM), X. Yi, Z. Liu, X. Tang, A. Zheng

Chemical Society Reviews

51, 11, 4337-4385

2022

Published while none of the authors were employed at the CMM

Abstract

Acid-catalyzed reactions inside zeolites are one type of broadly applied industrial reactions, where carbocations are the most common intermediates of these reaction processes, including methanol to olefins, alkene/aromatic alkylation, and hydrocarbon cracking/isomerization. The fundamental research on these acid-catalyzed reactions is focused on the stability, evolution, and lifetime of carbocations under the zeolite confinement effect, which greatly affects the efficiency, selectivity and deactivation of zeolite catalysts. Therefore, a profound understanding of the carbocations confined in zeolites is not only beneficial to explain the reaction mechanism but also drive the design of new zeolite catalysts with ideal acidity and cages/channels. In this review, we provide both an in-depth understanding of the stabilization of carbocations by the pore confinement effect and summary of the advanced characterization methods to capture carbocations in zeolites, including UV-vis spectroscopy, solid-state NMR, fluorescence microscopy, IR spectroscopy and Raman spectroscopy. Also, we clarify the relationship between the activity and stability of carbocations in zeolite-catalyzed reactions, and further highlight the role of carbocations in various hydrocarbon conversion reactions inside zeolites with diverse frameworks and varying acidic properties.

DOI

http://dx.doi.org/10.1039/d1cs00966d

Carbocation chemistry confined in zeolites: spectroscopic and theoretical characterizations

wei — Sat, 27 Jul 2024 03:40:00 +0000

W. Chen (Wei - CMM), X. Yi, Z. Liu, X. Tang, A. Zheng

Chemical Society Reviews

51, 11, 4337-4385

2022

Published while none of the authors were employed at the CMM

Abstract

DOI

http://dx.doi.org/10.1039/d1cs00966d

Protonated methylcyclopropane is an intermediate providing complete 13C-label scrambling at C4 olefin isomerization in zeolite

wei — Sat, 27 Jul 2024 03:24:31 +0000

W. Chen (Wei - CMM), M. Huang, X. Yi, Y. Hui, P. Gao, G. Hou, A. G. Stepanov, Y. Qin, L. Song, S.-B. Liu, Z. Chen, A. Zheng

Chem Catalysis

3, 2, 100503

2023

Published while none of the authors were employed at the CMM

Abstract

Carbocations play crucial roles during catalytic reactions by dictating the reaction pathways and genuine mechanisms, but the instability of carbocations prevents thorough observations. The stabilization of carbocations would greatly help us gain a deep understanding of the reaction mechanisms. By means of ab initio molecular dynamics (AIMD) simulations and an in situ experimental approach, a complete scrambling of 13C-labeled C4= products was observed during the isomerization reaction in the H-ZSM-5 zeolite at room temperature, and the corner-protonated methylcyclopropanes (as a non-classical carbocation) featuring the three-center two-electron (3c–2e) bonds were confirmed to be the highly active metastable intermediates of C4 isomerization. Our results not only uncover the nature of facile C shift in carbocations during zeolite-catalyzed reactions but also bring some fundamental understandings to carbocation chemistry in a zeolite confined environment.

DOI

http://dx.doi.org/10.1016/j.checat.2022.100503

Charge-separation driven mechanism via acylium ion intermediate migration during catalytic carbonylation in mordenite zeolite

wei — Sat, 27 Jul 2024 03:18:39 +0000

W. Chen (Wei - CMM), K. A. Tarach, X. Yi, Z. Liu, X. Tang, K. Góra-Marek, A. Zheng

Nature Communications

13, 7106

2022

Published while none of the authors were employed at the CMM

Abstract

By employing ab initio molecular dynamic simulations, solid-state NMR spectroscopy, and two-dimensional correlation analysis of rapid scan Fourier transform infrared spectroscopy data, a new pathway is proposed for the formation of methyl acetate (MA) via the acylium ion (i.e.,CH3 − C ≡ O+) in 12-membered ring (MR) channel of mordenite by an integrated reaction/diffusion kinetics model, and this route is kinetically and thermodynamically more favorable than the traditional viewpoint in 8MR channel. From perspective of the complete catalytic cycle, the separation of these two reaction zones, i.e., the C-C bond coupling in 8MR channel and MA formation in 12MR channel, effectively avoids aggregation of highly active acetyl species or ketene, thereby reducing undesired carbon deposit production. The synergistic effect of different channels appears to account for the high carbonylation activity in mordenite that has thus far not been fully explained, and this paradigm may rationalize the observed catalytic activity of other reactions.

Gold Open Access

DOI

http://dx.doi.org/10.1038/s41467-022-34708-5

Frustrated Lewis Pair in Zeolite Cages for Alkane Activations

wei — Sat, 27 Jul 2024 03:13:44 +0000

W. Chen (Wei - CMM), J. Han, Y. Wei, A. Zheng

Angewandte Chemie int. Ed.

61, e202116269

2022

Published while none of the authors were employed at the CMM

Abstract

The frustrated Lewis pair (FLP) concept in homogeneous catalysis was extended to heterogeneous catalysis via the supramolecular system of FLP between deprotonated zeolite framework oxygens and confined carbocations in methanol-to-olefin (MTO) reactions. In this FLP, the polymethylbenzenium (PMB+) functioned as the Lewis acid to accept an electron pair, and the deprotonated framework oxygen site acted as the Lewis base to donate an electron pair. This FLP theoretically demonstrated the ability to undergo H2 heterolysis and alkanes dehydrogenation, and this was further confirmed by gas chromatography–mass spectrometer (GC-MS) catalytic experiments inside FLP-containing chabazite zeolites. All these findings not only bring new recognition to the carbocation chemistry in zeolite cages but also put forward a new reaction pathway as one part of MTO reactions.

DOI

http://dx.doi.org/10.1002/anie.202116269

Molecular Understanding of the Catalytic Consequence of Ketene Intermediates under Confinement

wei — Sat, 27 Jul 2024 03:07:07 +0000

W. Chen (Wei - CMM), G. Li, X. Yi, S. J. Day, K. A. Tarach, Z. Liu, S.-B. Liu, S. C. E. Tsang, K. Góra-Marek, A. Zheng

JACS (Journal of the American Chemical Society)

143, 37, 15440–15452

2021

Published while none of the authors were employed at the CMM

Gold Open Access

DOI

http://dx.doi.org/10.1021/jacs.1c08036

Confinement Driven Dimethyl ether Carbonylation in Mordenite Zeolite as an Ultramicroscopic Reactor

wei — Mon, 01 Jul 2024 21:10:41 +0000

W. Chen (Wei - CMM), Z. Liu, X. Yi, A. Zheng

Accounts of Chemical Research

57, 19, 2804–2815

2024

Abstract

The conversion of C1 molecules to methyl acetate through the carbonylation of dimethyl ether in mordenite zeolite is an appealing reaction and a crucial step in the industrial coal-to-ethanol process. Mordenite zeolite has the large 12 membered ring (12MR) channels (7.0 Å × 6.5 Å) and small 8MR channels (5.7 Å × 2.6 Å) connected by a side pocket (4.8 Å × 3.4 Å), and this unique pore architecture supplies its high catalytic activity to the key step of carbonylation. However, the reaction mechanism of carbonylation in mordenite zeolite is not thoroughly established that be able to explain all experiment phenomena and improve its industrial applications, and the classical potential energy surface exerted by static density function theory calculations cannot reflect the reaction kinetics at realistic condition, because the diffusion kinetics of bulk DME (kinetic dimeter: 4.5 Å) and methyl acetate (MA, kinetic dimeter: 5.5 Å) were not well considered and their restrict diffusion in narrow side pocket and 8MR channels may greatly alter the integrated kinetics of DME carbonylation in mordenite zeolite. Moreover, the precise illustration of the dynamic behaviors of the ketene intermediate and its derivatives, specifically surface acetate and acylium ions, confined within various voids in mordenite, is not effectively portrayed. Advanced ab initio molecular dynamics (AIMD) simulations with or without the acceleration of enhanced sampling methods (metadynamics and umbrella sampling) provide tremendous opportunities for operando modeling of both reaction and diffusion processes and further identify the geometrical structure and chemical properties of the reactants, intermediates, and products in the different confined voids of mordenite under realistic reaction conditions, which enables high consistency between calculations and experiments, such as solid-state NMR, synchrotron radiation X-ray diffraction, and 2D correlation analysis of the FT-IR spectrum. In this account, the carbonylation process in mordenite is comprehensively described using the results of decades of continuous research and newly acquired knowledge from multiscale simulations and in situ or ex situ spectroscopic experiments. Three primary steps (DME demethylation to surface methyl species (SMS), carbon-carbon bond coupling between SMS and CO to acetyl species, and methyl acetate formation by acetyl species and methanol/DME) have been respectively studied with a careful consideration to different molecular factors (reactant’s distribution, concentration, and attacking mode). By utilizing the free energy surface of diffusion and reaction obtained from AIMD simulations, a comprehensive reaction/diffusion kinetics model was formulated for the first time, illustrating the entire zeolite catalytic process. In this context, a comprehensive and informative analysis of the reaction kinetics of carbonylation in mordenite, including the function of the 12MR channels, 8MR channels, and side pockets in the adsorption/diffusion/reaction of DME carbonylation, was performed. The mordenite channels contain a highly organized ultramicroscopic reactor that encompasses all ordered reaction steps.

DOI

http://dx.doi.org/10.1021/acs.accounts.4c00389