Mechanistic Aspects of the Zeolite Catalyzed Methylation of Alkenes and Aromatics with Methanol: A Review

Svelle, Stian; Visur, Melina; Olsbye, Unni; Saepurahman,; Bjørgen, Morten

doi:10.1007/s11244-011-9697-7

Cited by 114 publications

(123 citation statements)

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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%

“…[5,6,26] There is still an ongoing debate about the exact reaction mechanism, for which 6 two possible reaction routes have been proposed. [26] On the one hand, the methylation can occur in a concerted fashion, meaning that protonation of methanol, water formation and the methyl transfer occur simultaneously. On the other hand, there is the stepwise mechanism in which methanol protonation, water formation and the formation of a framework bound methoxide occur prior to the actual methylation.…”

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confidence: 99%

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

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

confidence: 99%

mentioning

confidence: 99%

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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“…While spectroscopic evidence for the existence of surface-bound methoxy groups has been presented, and the fundamental viability of a stepwise mechanism has been verified, experimental kinetic measurements are readily explained by the concerted pathway [26,28]. For this reason, the latter mechanism will be presumed in the current article.…”

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confidence: 99%

“…As far as the mechanism of the zeolite-catalyzed methylation reaction is concerned, two different proposals have been advocated in literature: a stepwise route that involves a surfacebound methoxy group intermediate, and a concerted mechanism in which physisorbed methanol directly interacts with the species to be methylated [22,26,27]. While spectroscopic evidence for the existence of surface-bound methoxy groups has been presented, and the fundamental viability of a stepwise mechanism has been verified, experimental kinetic measurements are readily explained by the concerted pathway [26,28].…”

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

Mynsbrugge

Visur

Olsbye

et al. 2012

Journal of Catalysis

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Benzene methylation by methanol is studied on acidic zeolites H-ZSM-5 (MFI) and H-beta (BEA) to investigate the influence of the catalyst topology on the reaction rate. Experimental kinetic measurements at 350 °C using extremely high feed rates to suppress side reactions show that methylation occurs considerably faster on H-ZSM-5 than on H-beta. Theoretical rate constants, obtained from first-principles simulations on extended zeolite clusters, reproduce a higher methylation rate on H-ZSM-5 and provide additional insight into the various molecular effects that contribute to the overall differences between the two catalysts. The calculations indicate this higher methylation rate is primarily due to an optimal confinement of the reacting species in the medium pore material. Co-adsorption of methanol and benzene is energetically favored in H-ZSM-5 compared with H-beta, to the extent that the stabilizing host-guest interactions outweigh the greater entropy loss upon benzene adsorption in H-ZSM-5 vs. in Hbeta.

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Chemistry ofCCBond Formation Reactions Used in Biomass Upgrading: Reaction Mechanisms, Site Requirements, and Catalytic Materials

Bui

Duong

Anaya

et al. 2019

Chemical Catalysts for Biomass Upgrading

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Mechanistic Aspects of the Zeolite Catalyzed Methylation of Alkenes and Aromatics with Methanol: A Review

Cited by 114 publications

References 68 publications

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

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

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

Chemistry ofCCBond Formation Reactions Used in Biomass Upgrading: Reaction Mechanisms, Site Requirements, and Catalytic Materials

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