Methylation of benzene by methanol: Single-site kinetics over H-ZSM-5 and H-beta zeolite catalysts

Mynsbrugge, Jeroen Van der; Visur, Melina; Olsbye, Unni; Beato, Pablo; Bjørgen, Morten; Speybroeck, Véronique Van; Svelle, Stian

doi:10.1016/j.jcat.2012.05.015

Cited by 129 publications

(148 citation statements)

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“…The role of catalyst topology has also extensively been studied for methylation reactions of alkenes and aromatics. 28,35,36,65 An optimal fit of the guest molecules in the zeolite pores seemed to be a determining factor for the reaction kinetics. 56 Next to reactivity, the catalyst topology and acidity were also found to impact diffusion rates of reaction products.…”

Section: Catalysis Science and Technology Papermentioning

confidence: 99%

“…Space -and time resolved spectroscopic techniques are nowadays able to image single particles and molecules 9,10,27 and kinetic measurements can yield information on isolated reaction steps. 28,29 Such kinetic information can at later instance be introduced in a micro-kinetic model to study the steadystate behavior of the process. [30][31][32][33] Also from a theoretical perspective many efforts to obtain profound understanding of the chemistry behind the MTH process have been performed and we refer the reader to some interesting reviews on this topic.…”

Section: Introductionmentioning

confidence: 99%

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Towards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditions

Wispelaere

Bailleul

Speybroeck

2016

Catal. Sci. Technol.

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Title: Towards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditions Advanced ab initio molecular dynamics techniques enable study of the infl uence of catalyst topology and acidity, reaction temperature and the presence of additional guest molecules on methylation reactions of benzene and propene, which are crucial reaction steps in the conversion of methanol into hydrocarbons. Our advanced simulations provide detailed insight into how operating conditions impact the competition of the concerted and stepwise methylation mechanism and thus the reaction kinetics. As featured in:See and mechanism of individual reaction steps at operating conditions. Herein we use state-of-the-art advanced ab initio molecular dynamics techniques to study the influence of catalyst topology and acidity, reaction temperature and the presence of additional guest molecules on elementary reactions. Such advanced modeling techniques provide complementary insight to experimental knowledge as the impact of individual factors on the reaction mechanism and kinetics of zeolite-catalyzed reactions may be unraveled. We study key reaction steps in the conversion of methanol to hydrocarbons, namely benzene and propene methylation. These reactions may occur either in a concerted or stepwise fashion, i.e. methanol directly transfers its methyl group to a hydrocarbon or the reaction goes through a framework-bound methoxide intermediate. The DFT-based dynamical approach enables mimicking reaction conditions as close as possible and studying the competition between two methylation mechanisms in an integrated fashion. The reactions are studied in the unidirectional AFI-structured H-SSZ-24, H-SAPO-5 and TON-structured H-ZSM-22 materials. We show that varying the temperature, topology, acidity and number of protic molecules surrounding the active site may tune the reaction mechanism at the molecular level. Obtaining molecular control is crucial in optimizing current zeolite processes and designing emerging new technologies bearing alternative feedstocks.

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Section: Catalysis Science and Technology Papermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Towards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditions

Wispelaere

Bailleul

Speybroeck

2016

Catal. Sci. Technol.

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“…[6] Consequently, numerous studies focused on the methylation by methanol, dimethyl ether or methoxides of aromatics and alkenes in the framework of the MTO process. [16,17,26,42,44,46,82,83] It should be mentioned that the static approach with finite cluster models as applied in most of these studies has been very successful in reproducing and predicting experimentally measured kinetic data. [16,17] However, a similar approach is not applicable for the study of methylation reactions in the large pore AFI structured H-SSZ-24 as will be demonstrated in this case study.…”

Section: Case Study Ii: Simulating Competing Pathways For Benzene Metmentioning

confidence: 99%

“…Similar observations were reported earlier for the methylation of benzene in H-ZSM-5 and H-Beta. [17] Step 1 (R-IM) 138.5 43.6…”

Section: Case Study Ii: Simulating Competing Pathways For Benzene Metmentioning

confidence: 99%

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Complex Reaction Environments and Competing Reaction Mechanisms in Zeolite Catalysis: Insights from Advanced Molecular Dynamics

Wispelaere

Ensing

Ghysels

et al. 2015

Chemistry A European J

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The methanol to olefins process is a show case example of complex zeolite-catalyzed chemistry. At real operating conditions, many factors such as framework flexibility, adsorption of various guest molecules and competitive reaction pathways, affect reactivity. In this paper we show the strength of first principle molecular dynamics techniques to capture this complexity by means of two case studies. Firstly, the adsorption behavior of methanol and water in H-SAPO-34 at 350 °C is investigated. Hereby we observed an important degree of framework flexibility and proton mobility. Secondly, we studied the methylation of benzene by methanol via a competitive direct and stepwise pathway in the AFI topology. Both case studies clearly show that a first principle molecular dynamics approach enables to obtain unprecedented insights into zeolite-catalyzed reactions at the nanometer scale.Keywords: ab initio calculations, molecular dynamics, proton mobility, methylation, zeolites 3 IntroductionChemical conversions in zeolites play an essential role in today's industrial catalysis. [1][2][3] Within the field of heterogeneous catalysis, the conversion of methanol to hydrocarbons (MTH) or olefins (MTO) over acidic zeolites received a lot of attention during the last decades, due to its relevance in the search for alternative processes to produce hydrocarbon products. [4][5][6][7] The MTO process has experimentally been developed in the past 3-4 decades and is currently being industrialized. [5] Methanol can be obtained from coal, natural gas or biomass and is in turn converted into ethene, propene or other hydrocarbons. The process proved extremely difficult to unravel at the nanoscale level due to various factors such as pressure, temperature and the occurrence of competing reaction mechanisms, which highly influence the catalytic performance of the system. Due to its complexity, it is a very challenging case study for theoretical modeling studies. [8] Currently, there is a consensus that a hydrocarbon pool (HP) mechanism operates during the methanol conversion process. Herein, an organic center is trapped in the zeolite pores and acts as co-catalyst. [9][10][11] The HP may be of aromatic or aliphatic nature and the two corresponding types of catalytic cycles are in close connection with each other, a concept that is called the dual cycle. [12] Depending on the catalyst topology and operating conditions either one or both cycles may be responsible for olefin formation during the methanol conversion process. [12][13][14] Theoretical contributions have proven to be indispensable within MTO research.Methodological developments and a steady increase in computer power, contributed to the fact that many properties, in particular rate coefficients of well-defined elementary reactions, are now routinely calculated with high accuracy. [8,[15][16][17] However, theoretical chemists are still confronted with paramount challenges to thoroughly explain experimental observations. The true challenge lies in linking the model system wit...

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Theoretical Tool Box for a Better Catalytic Understanding

Waroquier

Wispelaere

Hajek

et al. 2017

Nanotechnology in Catalysis

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Methylation of benzene by methanol: Single-site kinetics over H-ZSM-5 and H-beta zeolite catalysts

Cited by 129 publications

References 45 publications

Towards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditions

Towards molecular control of elementary reactions in zeolite catalysis by advanced molecular simulations mimicking operating conditions

Complex Reaction Environments and Competing Reaction Mechanisms in Zeolite Catalysis: Insights from Advanced Molecular Dynamics

Theoretical Tool Box for a Better Catalytic Understanding

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