Bridging the Gap between the Direct and Hydrocarbon Pool Mechanisms of the Methanol‐to‐Hydrocarbons Process

Chowdhury, Abhishek Dutta; Paioni, Alessandra Lucini; Houben, Klaartje; Whiting, Gareth T.; Baldus, Marc; Weckhuysen, Bert M.

doi:10.1002/anie.201803279

Cited by 112 publications

(194 citation statements)

References 50 publications

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“…The authors believed that these species were produced from the carbonylation reaction between CO and methoxy species, in agreement with previous report . The observation of these C−C bond species provides a route to bridge the direct and the indirect (HP) mechanisms . As shown in Scheme , after methyl acetate and acetic acid are formed, these species could be transformed into ketene by dehydration, which is followed by methylation with methanol and subsequent splitting off C 2 = −C 4 = as the initial alkenes.…”

Section: C1 Species and C−c Bond Formationsupporting

confidence: 84%

Mechanism of Methanol‐to‐hydrocarbon Reaction over Zeolites: A solid‐state NMR Perspective

Wang¹,

Xu²

2020

ChemCatChem

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The versatile methanol‐to‐hydrocarbon (MTH) process on acidic zeolites allows for a production of olefins, aromatics and gasoline from a wide range of non‐fossil resources. Elucidation of the MTH reaction mechanism is helpful to improve product selectivity as well as develop high performance catalysts. The application of solid‐state NMR in the investigation of MTH reaction has significantly contributed to get insight into the MTH chemistry. In this review, we summarize mechanistic insight that has been gained into the MTH reaction by using solid‐state NMR spectroscopy. Special emphasis is given to the observation and determination of C1 species and active intermediates particularly cyclic carbocations to uncover the exact reaction route for the initial C−C bond formation and the hydrocarbon pool mechanism. The detection of host‐guest interactions involved in the MTH reaction with the advanced 13C‐27Al double‐resonance NMR is discussed for a better understanding of the active sites and the reactivity of hydrocarbon pool species.

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Section: C1 Species and C−c Bond Formationsupporting

confidence: 84%

Mechanism of Methanol‐to‐hydrocarbon Reaction over Zeolites: A solid‐state NMR Perspective

Wang¹,

Xu²

2020

ChemCatChem

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“…[13,19,20] Despite being commercialized, the MTO process still draws a lot of attention from both academia and industry due to its complex reaction mechanism. [8][9][10]28,29] Intensive research performed in the last decades to elucidate the complex MTO reaction mechanism led to the general acceptance of the hydrocarbon pool (HP) mechanism. In this mechanism, an organic compound that is trapped in the catalyst pores acts as a co-catalyst.…”

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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“…Various direct mechanisms have been proposed for the conversion of methanol/DME to primary olefins. 12 These direct mechanisms are known by their intermediates and include oxonium ylide, 13,14 carbene, 15 methane-formaldehyde, 16,17 carbon monoxide, [18][19][20] methoxymethyl, 21,22 and surface methoxy groups. [23][24][25][26] Using density functional theory (DFT) calculations, Lesthaeghe et al [27][28][29] refuted some direct mechanisms based on high activation energy barriers and highly unstable intermediates.…”

mentioning

confidence: 99%

“…Nonetheless, the methoxymethyl pathway was more kinetically and thermodynamically favorable. Liu et al, 18 Chowdhury et al, 19,20 and Plessow and Studt 33,34 provided spectroscopic and theoretical evidence for a carbon monoxide mechanism. The formation of the first C-C bond (surface acetate group) was shown to involve a low activation barrier of 80 kJ mol −1 .…”

mentioning

confidence: 99%

“…This was also evidenced by Liu et al 18 and Wei et al 21 In this paper, we investigate the induction period during the formation of primary olefins from DME at 300 • C by conducting novel step response experiments in a temporal analysis of products (TAP) reactor. Nine reaction schemes obtained from the literature [18][19][20][21][22] were compared and used as a basis for a microkinetic model. The experimental data were simulated to extract kinetic parameters that describe the formation of primary olefins from DME over fresh ZSM-5 catalysts.…”

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confidence: 99%

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Transient kinetic studies and microkinetic modeling of primary olefin formation from dimethyl ether over ZSM‐5 catalysts

Omojola

Lukyanov

Veen

2019

Int J of Chemical Kinetics

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The formation of primary olefins from dimethyl ether (DME) was studied over ZSM‐5 catalysts at 300°C using a novel step response methodology in a temporal analysis of products (TAP) reactor. For the first time, the TAP reactor framework was used to conduct single‐ and multiple‐step response cycles of DME (balance argon) over a shallow bed with the continuous flow panel. Propylene is the major primary olefin and portrays an S‐shaped profile with a preceding induction period when it is not observed in the gas phase. Methanol and water portray overshoot profiles due to their different rates of generation and consumption. DME effluent shows a rapid rise halfway to its steady‐state value leading to a slow rise thereafter because of its high desorption rates followed by subsequent reactions involving DME in further steps during the induction period. To analyze the experimental data quantitatively, nine reaction schemes were compared, and kinetic parameters were obtained by solving a transient plug flow reactor model with coupled dispersion, convection, adsorption, desorption, and reaction steps. The methoxymethyl pathway involving dimethoxyethane and methyl propenyl ether gives the closest match to experimental data in agreement with recent density functional theory studies. Gaseous dispersion coefficients of ca. 10−9 m2 s−1 were obtained in the TAP reactor. The novel experimental data validated against the transient kinetic model suggests that after the formation of initial species, the bottleneck in propylene formation is the transformation of the initial C–C bond, that is dimethoxyethane formed initially from DME and methoxymethyl groups. DME adsorption on ZSM‐5 catalyst generates surface methoxy groups, which further react with the feed to give methoxymethyl groups. These methoxymethyl groups are regenerated through a series of reactions involving intermediates such as dimethoxymethane and methyl propenyl ether before propylene formation.

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Bridging the Gap between the Direct and Hydrocarbon Pool Mechanisms of the Methanol‐to‐Hydrocarbons Process

Cited by 112 publications

References 50 publications

Mechanism of Methanol‐to‐hydrocarbon Reaction over Zeolites: A solid‐state NMR Perspective

Mechanism of Methanol‐to‐hydrocarbon Reaction over Zeolites: A solid‐state NMR Perspective

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

Transient kinetic studies and microkinetic modeling of primary olefin formation from dimethyl ether over ZSM‐5 catalysts

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