Methylation of Ethene by Surface Methoxides: A Periodic PBE+D Study across Zeolites

Mazar, M. N.; Al-Hashimi, Saleh; Bhan, Aditya; Cococcioni, Matteo

doi:10.1021/jp306003e

Cited by 30 publications

(34 citation statements)

References 106 publications

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“…A number of theoretical studies already addressed the importance of a stepwise mechanism. [73,[81][82][83]. In particular, it has been reported the stepwise mechanism becomes important at high temperature due to the entropic effect of the intermediate release of a water molecule [73,82].…”

Section: Adsorption Behaviour From Molecular Dynamics Simulationsmentioning

confidence: 99%

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

Erichsen

Wispelaere

Hemelsoet

et al. 2015

Journal of Catalysis

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a b s t r a c tThis 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°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 C 4+ 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°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.

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Section: Adsorption Behaviour From Molecular Dynamics Simulationsmentioning

confidence: 99%

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

Erichsen

Wispelaere

Hemelsoet

et al. 2015

Journal of Catalysis

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“…In this stepwise mechanism, methanol first reacts with the catalyst framework, forming a methoxide species, which then transfers its methyl group to the HP species . Literature suggests that both mechanisms occur within the zeolite and the prevailing mechanism largely depends on the topology and the operating conditions . The studies show that with increasing temperature and decreasing pressure the prevailing mechanism shifts from concerted to stepwise .…”

Section: Introductionmentioning

confidence: 99%

“…[38][39][40][41][42][43][44] Literature suggests that both mechanisms occur within the zeolite and the prevailing mechanism largely depends on the topology and the operating conditions. [40][41][42][43][44][45][46][47][48][49] The studies show that with increasing temperature and decreasing pressure the prevailing mechanism shifts from concerted to stepwise. [45] This effect is attributed to the entropic gain of the intermediate release of water during the stepwise mechanism.…”

Section: Introductionmentioning

confidence: 99%

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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“…Then, they identified the number of van der Waals interactions and calculated the E LDE of the species of interest by applying the appropriate van der Waals coefficients. 7 De Moor and co-workers studied adsorption of alkanes in zeolites and showed that smaller pores lead to a tighter fit of adsorbates and thus to stronger adsorption, mainly due to higher contributions of the stabilizing van der Waals interactions between the n-alkane and the zeolite. 8 According to Sacchetto and co-workers, the knowledge of host−guest interactions occurring in zeolites could be helpful to improve adsorption properties of these materials, thus extending their application fields.…”

Section: Introductionmentioning

confidence: 99%

Study of Confinement and Catalysis Effects of the Reaction of Methylation of Benzene by Methanol in H-Beta and H-ZSM-5 Zeolites by Topological Analysis of Electron Density

et al. 2018

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In this work we studied the host–guest interactions between confined molecules and zeolites and their relationship with the energies involved in the reaction of methylation of benzene by methanol in H-ZSM-5 and H-Beta zeolites employing density functional theory (DFT) methods and the quantum theory of atoms in molecules. Results show that the strength of the interactions related to adsorption and coadsorption processes is higher in the catalyst with the larger cavity; however, the confinement effects are higher in the smaller zeolite, explaining, from an electronic viewpoint, the reason why the stabilization energy is higher in H-ZSM-5 than in H-Beta. The confinement effects of the catalyst on the confined species for methanol adsorption, benzene coadsorption, and the formed intermediates dominate this stabilization. For the transition state (TS), the stability of the TS is achieved due to the stabilizing effect of the surrounding zeolite framework on the formed carbocationic species (CH3 +) which is higher in H-ZSM-5 than in H-Beta. In both TSs the methyl cation is multicoordinated forming the following H2O···CH3 +···CB concerted bonds. It is demonstrated that, through the electron density analysis, the criteria can be defined to discriminate between interactions related to the confinement effects and the reaction itself (adsorption, coadsorption, and bond-breaking and bond-forming processes) and, thus, to discriminate the relative contributions of the degree of confinement to the reaction energies for two zeolite catalysts with different topologies.

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Methylation of Ethene by Surface Methoxides: A Periodic PBE+D Study across Zeolites

Cited by 30 publications

References 106 publications

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

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

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

Study of Confinement and Catalysis Effects of the Reaction of Methylation of Benzene by Methanol in H-Beta and H-ZSM-5 Zeolites by Topological Analysis of Electron Density

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