A Re-Examination of Evidence for Carbene (CH2:) As An Intermediate in the Conversion of Methanol to Gasoline. The Effect of Added Propane

Dass, D.V.; Martin, R. Wayne; Odell, A. L.; Quinn, G

doi:10.1016/s0167-2991(09)60510-3

Cited by 7 publications

(5 citation statements)

References 4 publications

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“…They linked lower iso/normal (butane) ratios to sp 3 insertion of carbene into H–C bonds. Furthermore, Dass and colleagues also came to a similar conclusion after investigations on methanol–propane interactions over ZSM-5. Besides these experimental approaches, computational chemists have also focused on the formation and stabilization of carbenes in zeolite catalyzed MTH reactions. − Overall, computational studies revealed that it is energy demanding to form carbenes from surface methoxy groups; however, its bonding on the zeolite framework is strong enough to remain stable to further react with other molecules.…”

Section: Carbene Chemistry In Zeolite Catalysismentioning

confidence: 64%

“…Nonetheless, all of these were hypothetical; there was even no indirect evidence showing the presence of carbenes in zeolite catalyzed MTH reactions at that time. In the 1980s, some researchers attempted to provide experimental evidence of carbenes in the MTH reaction network. − However, all of these provided only indirect evidence; they were based on mechanistic discussions constructed on the products obtained upon the reaction. For instance, Chang and Chu interpreted the carbene formation and participation in MTH chemistry through butane isomer ratios (iso/normal) upon the reaction of the 13 C labeled methanol and unlabeled propane over ZSM-5 .…”

Section: Carbene Chemistry In Zeolite Catalysismentioning

confidence: 99%

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First-Generation Organic Reaction Intermediates in Zeolite Chemistry and Catalysis

Gong

Çağlayan

et al. 2022

Chem. Rev.

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Zeolite chemistry and catalysis are expected to play a decisive role in the next decade(s) to build a more decentralized renewable feedstock-dependent sustainable society owing to the increased scrutiny over carbon emissions. Therefore, the lack of fundamental and mechanistic understanding of these processes is a critical “technical bottleneck” that must be eliminated to maximize economic value and minimize waste. We have identified, considering this objective, that the chemistry related to the first-generation reaction intermediates (i.e., carbocations, radicals, carbenes, ketenes, and carbanions) in zeolite chemistry and catalysis is highly underdeveloped or undervalued compared to other catalysis streams (e.g., homogeneous catalysis). This limitation can often be attributed to the technological restrictions to detect such “short-lived and highly reactive” intermediates at the interface (gas–solid/solid–liquid); however, the recent rise of sophisticated spectroscopic/analytical techniques (including under in situ/operando conditions) and modern data analysis methods collectively compete to unravel the impact of these organic intermediates. This comprehensive review summarizes the state-of-the-art first-generation organic reaction intermediates in zeolite chemistry and catalysis and evaluates their existing challenges and future prospects, to contribute significantly to the “circular carbon economy” initiatives.

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Section: Carbene Chemistry In Zeolite Catalysismentioning

confidence: 64%

Section: Carbene Chemistry In Zeolite Catalysismentioning

confidence: 99%

First-Generation Organic Reaction Intermediates in Zeolite Chemistry and Catalysis

Gong

Çağlayan

et al. 2022

Chem. Rev.

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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%

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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“…Several mechanisms have been used to describe the induction period of the methanol-to-olefin conversion over zeolite catalysts. These include: (1) carbene, − (2) carbon monoxide, − (3) methane-formaldehyde, − and (4) methoxymethyl cation. , Each mechanism involves a similar set of steps, namely: adsorption and desorption of methanol, dimethyl ether, and water, olefin (ethylene and/or propylene) formation, and release. These adsorption and desorption steps occur as the catalysts evolve from fresh catalysts to working catalysts at steady-state.…”

Section: Resultsmentioning

confidence: 99%

Site-Specific Activity Maps Observed during Methanol-to-Olefin Conversion over ZSM-5 Catalysts

Omojola

2024

Ind. Eng. Chem. Res.

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The Sabatier principle has been applied to nonuniform site ensembles of ZSM-5 catalysts of different compositions (Si/Al = 25, 36, and 135) during the induction period of the conversion of methanol and dimethyl ether to propylene. For the first time, site-specific volcano-plots and site-specific activity-maps have been observed following microkinetic simulations of the temperature-programmed surface reaction of methanol and dimethyl ether over ZSM-5 catalysts in a temporal analysis of products reactor. The microkinetic simulations are constructed using coupled 1D nonlinear partial differential equations that connect reactions at the active site to convection and dispersion through the reactor. The methoxymethyl cation pathway predicts the formation of propylene from methanol and dimethyl ether via dimethoxyethane. Site-specific scaling relations are observed between the acid site density and the barriers of the dissociative desorption of dimethyl ether with the barrier of methoxymethyl cation formation during the induction period of propylene formation from methanol and dimethyl ether, respectively. During the induction period of methanol conversion to propylene, depending on the barrier to methoxymethyl cation formation, the active site density should not be too low such that site cooperation is inhibited and not too high such that site competition is promoted. The optimum site density is ca. 5 × 10–4 mmol g–1 of active sites over the high-temperature active sites of ZSM-5 (Si/Al = 36) catalysts. Over the high-temperature active sites on ZSM-5 (25) catalysts, we observe a maximum rate of propylene formation at an optimum site density of 7 × 10–4 mmol g–1 active sites. During the induction period of dimethyl ether conversion, the binding energies should not be too weak to activate dimethyl ether and not too strong to inhibit its release into the gas phase. The binding energy of methoxymethyl cation should be between −80 kJ mol–1 and −100 kJ mol–1 for maximum propylene formation over the low-temperature active sites of ZSM-5 (Si/Al = 36) catalysts. Over the medium-temperature active sites of ZSM-5 (Si/Al = 36) catalysts, the maximum rate constant of propylene formation is observed between a binding energy of dimethyl ether of −135 kJ mol–1 and −145 kJ mol–1. The site-specific activity maps show that the catalytic activity of methanol-to-olefin conversion varies across the different site ensembles. In each site-specific activity map, the direction of the maximum rate constant of propylene formation changes with zeolite composition and site-ensemble. The precision given by this site-specific control shows that the catalytic activity can be tailored to the site characteristics.

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A Re-Examination of Evidence for Carbene (CH2:) As An Intermediate in the Conversion of Methanol to Gasoline. The Effect of Added Propane

Cited by 7 publications

References 4 publications

First-Generation Organic Reaction Intermediates in Zeolite Chemistry and Catalysis

First-Generation Organic Reaction Intermediates in Zeolite Chemistry and Catalysis

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

Site-Specific Activity Maps Observed during Methanol-to-Olefin Conversion over ZSM-5 Catalysts

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