Mechanism Studies of the Fischer-Tropsch Synthesis: The Incorporation of Radioactive Ethylene, Propionaldehyde and Propanol

Hall, W. Keith; Kokes, R. J.; Emmett, P. H.

doi:10.1021/ja01490a005

Cited by 126 publications

(45 citation statements)

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“…Popular pathways include (i) the ''carbide'' theory, originally proposed by Fischer and Tropsch [1], which involves direct CO adsorption and dissociation and subsequent hydrogenation of chemisorbed carbide (C*) to form chemisorbed *CH x monomer and (ii) the ''enolic'' theory, proposed by Storch et al [22] 25 years after the work of Fischer and Tropsch, involving chemisorption of CO molecules and the formation of oxygen-containing intermediates, the enol (HC*OH (hydroxycarbene)), whose condensation is responsible for the formation of the first C-C bond in each hydrocarbon product. Several other proposals have followed; they can be grouped into those involving direct dissociation of chemisorbed CO, followed by reaction of its C* and O* products (referred to as ''unassisted CO dissociation'') [23][24][25][26][27][28][29], and those in which chemisorbed hydrogen atoms add to chemisorbed CO molecules before the C-O bond cleavage (''hydrogenassisted CO dissociation'') [7,[29][30][31]. Both theories, i.e.…”

Section: Reaction Schemementioning

confidence: 99%

Detailed Kinetics of the Fischer–Tropsch Synthesis on Cobalt Catalysts Based on H-Assisted CO Activation

et al. 2011

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A complete mechanistic kinetic model of the Fischer-Tropsch synthesis (FTS) over a Co/Al 2 O 3 stateof-the-art catalyst is developed here under conditions relevant to industrial operation. On the basis of the most recent findings on the reaction mechanism, here described according to the H-assisted CO dissociation theory and the alkyl chain growth mechanism, and on the basis of the latest indications available on the rate determining step involved in the CO activation process, rate expressions for all the steps leading to CO and H 2 consumption and n-paraffins, a-olefins and H 2 O formation are derived. Such expressions are functions of the molar fraction of CO, H 2 and olefins in the liquid phase surrounding the catalyst pellets, that in turn are related to the gas-phase pressure and composition, and of the surface coverage of the adsorbed species. Thermodynamic and kinetic parameters involved in the model are estimated by nonlinear multi-response regression on a complete set of FTS experimental data collected in a lab-scale tubular reactor at steady-state conditions (P = 8-25 bar, T = 210-235°C, H 2 /CO feed ratio = 1.8-2.7 mol mol -1 , GHSV = 2,000-7,000 cm 3 (STP) h -1 g cat -1). Both the experimental CO conversion and the hydrocarbon distribution (up to N = 50) in FTS are well predicted by the model with 13 adaptive parameters, without the need of introducing any empirical parameter. Analysis of the model offers insight in the rates of the elementary steps associated with the reaction mechanism and in the surface coverages of the adsorbed species. Such information explains the peculiar reactivity observed over cobalt-based Fischer-Tropsch catalysts, and can provide guidelines for the design of more active and selective catalytic materials.

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Section: Reaction Schemementioning

confidence: 99%

Detailed Kinetics of the Fischer–Tropsch Synthesis on Cobalt Catalysts Based on H-Assisted CO Activation

et al. 2011

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“…Thus, total number of Brønsted acid sites presented in zeolite catalyst was depended on the aluminum framework. It was concluded that the frequencies of the strong vibrational modes observed between 400 and 1200 cm À1 in infrared spectra were depended on the zeolite aluminum content and could be used to determine the framework aluminum content of dealuminated zeolites (Hensen et al, 2004;Campbell et al, 1996a,b). Table 2 shows the aluminum framework determined in the fresh and used zeolites.…”

Section: Reduction Behavior Of the Catalystmentioning

confidence: 99%

Catalytic behaviors of bifunctional Fe-HZSM-5 catalyst in Fischer–Tropsch synthesis

Pour

Zare

Shahri

et al. 2009

Journal of Natural Gas Science and Engineering

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“…In contrast, the 'enol' mechanism [8,9] involves hydroxymethylenes (HCOH) formed by hydrogenation of adsorbed CO, which undergo condensation in the chain propagation step [16,17]. A third possibility is the COinsertion mechanism, in which CO undergoes hydrogenation and C-O bond scission to form an alkyl chain initiator, followed by insertion of CO which acts as the chain propagator [8,9].…”

Section: Introductionmentioning

confidence: 99%

CO Dissociation at Vacancy Sites on Hägg Iron Carbide: Direct Versus Hydrogen-Assisted Routes Investigated with DFT

Petersen

Rensburg

2015

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The mechanism of activation of CO remains under debate in Fe-catalysed Fischer-Tropsch synthesis, in which iron carbides form under reaction conditions. Direct and H-assisted paths for CO activation and dissociation are investigated at carbon vacancy and non-vacancy sites on the Fe 5 C 2 (010) surface of Hägg iron carbide using density functional theory. The calculated overall energy barrier for direct and for H-assisted dissociation of CO via formation of an HCO intermediate is the same, 1.42 and 1.41 eV, respectively, but the lowest energy paths are facilitated by different vacancy sites. Furthermore, dissociation at a nonvacancy site is only marginally higher in energy by 0.1 eV. Dissociation through formation of a hydroxymethylidyne (COH) intermediate is less competitive kinetically.

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Mechanism Studies of the Fischer-Tropsch Synthesis: The Incorporation of Radioactive Ethylene, Propionaldehyde and Propanol

Cited by 126 publications

References 0 publications

Detailed Kinetics of the Fischer–Tropsch Synthesis on Cobalt Catalysts Based on H-Assisted CO Activation

Detailed Kinetics of the Fischer–Tropsch Synthesis on Cobalt Catalysts Based on H-Assisted CO Activation

Catalytic behaviors of bifunctional Fe-HZSM-5 catalyst in Fischer–Tropsch synthesis

CO Dissociation at Vacancy Sites on Hägg Iron Carbide: Direct Versus Hydrogen-Assisted Routes Investigated with DFT

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