Brønsted/Lewis acid sites synergistically promote the initial C–C bond formation in the MTO reaction

Chu, Y. P.; Yi, Xiaoyan; Li, Chengbin; Sun, Xianyong; Zheng, Anmin

doi:10.1039/c8sc02302f

Cited by 63 publications

(34 citation statements)

References 47 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Lastly, we focus on Brønsted acid sites, as they are present in the pores of the zeolite. However, other active site motifs such as surface Brønsted and Lewis acid sites [91][92][93][94], as well as extra-framework aluminum sites [50] may also play an important role.…”

Section: Methodsmentioning

confidence: 99%

Effect of Impurities on the Initiation of the Methanol-to-Olefins Process: Kinetic Modeling Based on Ab Initio Rate Constants

2021

View full text Add to dashboard Cite

The relevance of a selection of organic impurities for the initiation of the MTO process was quantified in a kinetic model comprising 107 elementary steps with ab initio computed reaction barriers (MP2:DFT). This model includes a representative part of the autocatalytic olefin cycle as well as a direct initiation mechanism starting from methanol through CO-mediated direct C–C bond formation. We find that the effect of different impurities on the olefin evolution varies with the type of impurity and their partial pressures. The reactivity of the considered impurities for initiating the olefin cycle increases in the order formaldehyde < di-methoxy methane < CO < methyl acetate < ethanol < ethene < propene. In our kinetic model, already extremely low quantities of impurities such as ethanol lead to faster initiation than through direct C–C bond formation which only matters in complete absence of impurities. Graphic Abstract

show abstract

Section: Methodsmentioning

confidence: 99%

Effect of Impurities on the Initiation of the Methanol-to-Olefins Process: Kinetic Modeling Based on Ab Initio Rate Constants

2021

View full text Add to dashboard Cite

show abstract

“…Zheng and co‐authors recently postulated a new synergetic reaction mechanism for the MTO reaction. They proposed that Brønsted‐Lewis acid synergy is necessary for the initial C−C bond formation within the MTO reaction . The proposed mechanism involves the methane‐formaldehyde reaction pathway promoted by a cooperation between the proton of the BAS and a LAS of a vicinal EFAl species.…”

Section: Beyond the Single‐site Approximation: Cooperative And Synergmentioning

confidence: 99%

“… Proposed mechanism of C−C bond formation at the synergistic Brønsted/Lewis acid sites in zeolite for methanol to olefin reaction . Reprinted with permission from Chem.…”

Section: Beyond the Single‐site Approximation: Cooperative And Synergmentioning

confidence: 99%

The Nature and Catalytic Function of Cation Sites in Zeolites: a Computational Perspective

Pidko

2018

ChemCatChem

104

View full text Add to dashboard Cite

Zeolites have a broad spectrum of applications as robust microporous catalysts for various chemical transformations. The reactivity of zeolite catalysts can be tailored by introducing heteroatoms either into the framework or at the extraframework positions that gives rise to the formation of versatile Brønsted acid, Lewis acid and redox‐active catalytic sites. Understanding the nature and catalytic role of such sites is crucial for guiding the design of new and improved zeolite‐based catalysts. This work presents an overview of recent computational studies devoted to unravelling the molecular level details of catalytic transformations inside the zeolite pores. The role of modern computational chemistry in addressing the structural problem in zeolite catalysis, understanding reaction mechanisms and establishing structure‐activity relations is discussed. Special attention is devoted to such mechanistic phenomena as active site cooperativity, multifunctional catalysis as well as confinement‐induced and multisite reactivity commonly encountered in zeolite catalysis.

show abstract

“…using a similar technical setup to analyse methyl transfer from the active site to olefins, we find that methyl transferring from the active site to ethene (ΔFforward = 123 kJ/mol), propene (ΔFforward = 112 kJ/mol) or trans-2-butene (ΔFforward = 108 kJ/mol) 60 , is more favourable than framework migration, indicating that in the presence of the hydrocarbon pool, methyl is unlikely to translate but rather to transfer to olefins. Also, previous studies proposed ethoxyde as an intermediate 74,75 which in our case, could be formed via a carbene insertion to methoxyde.…”

Section: Figure 5 Illustrations Of Reactions Considered For Methyl Bonded On Oal When Converted To Hydrogen and A Carbene Bonded Between mentioning

confidence: 50%

QM/MM Study of the Reactivity of Zeolite Bound Methoxy and Carbene Groups

Logsdail

Catlow²,

Nastase³

2021

Preprint

View full text Add to dashboard Cite

<div>The conversion of methanol-to-hydrocarbons (MTH) is known to occur via an autocatalytic process in zeolites, where framework-bound methoxy species play a pivotal role, especially during catalyst induction. Recent NMR and FT-IR experimental studies suggest that methoxylated zeolites are able to produce hydrocarbons by a mechanism involving carbene migration and association. In order to understand these observations, we have performed QM/MM computational investigations on a range of reaction mechanisms for the reaction of zeolite bound methoxy and carbene groups, which are proposed to initiate hydrocarbon formation in the MTH process. Our simulations demonstrate that it is kinetically unfavourable for methyl species to form on the framework away from the zeolite acid site, and both kinetically and thermodynamically unfavourable for methyl groups to migrate through the framework and aggregate around an acid site. Formation of carbene moieties was considered as an alternative pathway to the formation of C-C bonds; however, the reaction energy for conversion of a methyl to a carbene is unfavourable. Metadynamics simulations help confirm further that methyl species at the framework acid sites would be more reactive towards formed C<sub>2+</sub> species, rather than inter-framework migration and that the role of carbenes in the formation of the first –C bond will be via a concerted type of mechanism rather than stepwise. </div>

show abstract

Brønsted/Lewis acid sites synergistically promote the initial C–C bond formation in the MTO reaction

Abstract: The Lewis acid site combined with a Brønsted acid site in zeolite catalysts facilitates first C–C bond formation in the initiation step of the MTO reaction.

Cited by 63 publications

References 47 publications

Effect of Impurities on the Initiation of the Methanol-to-Olefins Process: Kinetic Modeling Based on Ab Initio Rate Constants

Effect of Impurities on the Initiation of the Methanol-to-Olefins Process: Kinetic Modeling Based on Ab Initio Rate Constants

The Nature and Catalytic Function of Cation Sites in Zeolites: a Computational Perspective

QM/MM Study of the Reactivity of Zeolite Bound Methoxy and Carbene Groups

Contact Info

Product

Resources

About