On the origin of the difference between type A and type B skeletal isomerization of alkenes catalyzed by zeolites: The crucial input of ab initio molecular dynamics

Rey, Jérôme; Gomez, Axel; Raybaud, Pascal; Chizallet, Céline

doi:10.1016/j.jcat.2019.04.014

Cited by 46 publications

(97 citation statements)

References 82 publications

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“…The error bars are also reported in Table S4 and Table S5. Before discussing in depth the numerical results, it is important to acknowledge that obtaining accurate free energies from enhanced sampling molecular dynamics simulations is extremely challenging, certainly when the sampling has been performed based on first principle simulations which poses limits on the number of simulations and the length of the simulations that may be performed within a feasible computational time . For the interested reader an estimate of the computational time used for the reactions under study has been given in Table S6 of the ESI.…”

Section: Resultsmentioning

confidence: 99%

“…As reviewed earlier, the accuracy of the final results depends on the level of theory used to describe the system, the sampling protocol, and the estimator to obtain the free energy differences . For DFT based reactions in zeolites only a few works are available which assess each of the components on the finally obtained free energies …”

Section: Resultsmentioning

confidence: 99%

“…enhanced sampling molecular dynamics simulations is extremely challenging, certainly when the sampling has been performed based on first principle simulations which poses limits on the number of simulations and the length of the simulations that may be performed within a feasible computational time. [55] For the interested reader an estimate of the computational time used for the reactions under study has been given in Table S6 of the ESI. As reviewed earlier, the accuracy of the final results depends on the level of theory used to describe the system, the sampling protocol, and the estimator to obtain the free energy differences.…”

Section: Influence Of Water On the Reaction Free Energy Profilementioning

confidence: 99%

“…The temperature and entropic effects make this reaction especially interesting to demonstrate the importance of a good description of the reaction conditions and entropic contributions using dynamic methods instead of static modeling techniques. Recent theoretical modeling work is more and more focused on the use of molecular dynamic (MD) techniques . Nevertheless, regular MD simulations have the disadvantage of mainly sampling the most probable regions of the phase space making the elementary reactions that are interesting in most reaction mechanism rare events and thus difficult to examine.…”

Section: Introductionmentioning

confidence: 99%

“…Recent theoretical modeling work is more and more focused on the use of molecular dynamic (MD) techniques. [13,28,[50][51][52][53][54][55] Nevertheless, regular MD simulations have the disadvantage of mainly sampling the most probable regions of the phase space making the elementary reactions that are interesting in most reaction mechanism rare events and thus difficult to examine. This hurdle can be overcome via enhanced sampling methods that steer the system to cross the reaction barrier.…”

Section: Introductionmentioning

confidence: 99%

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Insight into the Role of Water on the Methylation of Hexamethylbenzene in H‐SAPO‐34 from First Principle Molecular Dynamics Simulations

et al. 2019

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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.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Influence Of Water On the Reaction Free Energy Profilementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Insight into the Role of Water on the Methylation of Hexamethylbenzene in H‐SAPO‐34 from First Principle Molecular Dynamics Simulations

et al. 2019

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Dynamic Features of Transition States for β‐Scission Reactions of Alkenes over Acid Zeolites Revealed by AIMD Simulations

et al. 2020

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Zeolite-catalyzed alkene cracking is key to optimize the size of hydrocarbons. The nature and stability of intermediates and transition states (TS) are, however, still debated. We combine transition path sampling and blue moon ensemble density functional theory simulations to unravel the behavior of C 7 alkenes in CHA zeolite. Free energy profiles are determined, linking p-complexes, alkoxides and carbenium ions, for B 1 (secondary to tertiary) and B 2 (tertiary to secondary) b-scissions. B 1 is found to be easier than B 2. The TS for B 1 occurs at the breaking of the CÀC bond, while for B 2 it is the proton transfer from propenium to the zeolite. We highlight the dynamic behaviors of the various intermediates along both pathways, which reduce activation energies with respect to those previously evaluated by static approaches. We finally revisit the ranking of isomerization and cracking rate constants, which are crucial for future kinetic studies. Scheme 1. b-scission mechanisms: a) type B 1 involving secondary 4,4dimethyl-penten-2-ium to tertiary tert-butylium cation. b) type B 2 involving tertiary 2,4-dimethyl-penten-2-ium to secondary propenium cation.

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Reference‐Quality Free Energy Barriers in Catalysis from Machine Learning Thermodynamic Perturbation Theory

Rey,

Chizallet,

Rocca

et al. 2023

Angewandte Chemie

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For the first time, we report calculations of the free energies of activation of cracking and isomerization reactions of alkenes that combine several different electronic structure methods with molecular dynamics simulations. We demonstrate that the use of a high level of theory (here Random Phase Approximation—RPA) is necessary to bridge the gap between experimental and computed values. These transformations, catalyzed by zeolites and proceeding via cationic intermediates and transition states, are building blocks of many chemical transformations for valorization of long chain paraffins originating, e.g., from plastic waste, vegetable oils, Fischer–Tropsch waxes or crude oils. Compared with the free energy barriers computed at the PBE+D2 production level of theory via constrained ab initio molecular dynamics, the barriers computed at the RPA level by the application of Machine Learning thermodynamic Perturbation Theory (MLPT) show a significant decrease for isomerization reaction and an increase of a similar magnitude for cracking, yielding an unprecedented agreement with the results obtained by experiments and kinetic modeling.

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On the origin of the difference between type A and type B skeletal isomerization of alkenes catalyzed by zeolites: The crucial input of ab initio molecular dynamics

Cited by 46 publications

References 82 publications

Insight into the Role of Water on the Methylation of Hexamethylbenzene in H‐SAPO‐34 from First Principle Molecular Dynamics Simulations

Insight into the Role of Water on the Methylation of Hexamethylbenzene in H‐SAPO‐34 from First Principle Molecular Dynamics Simulations

Dynamic Features of Transition States for β‐Scission Reactions of Alkenes over Acid Zeolites Revealed by AIMD Simulations

Reference‐Quality Free Energy Barriers in Catalysis from Machine Learning Thermodynamic Perturbation Theory

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