Mechanism of Carbon Monoxide Dissociation on a Cobalt Fischer–Tropsch Catalyst

Chen, W Wei; Zijlstra, Bart; Filot, Ivo A. W.; Pestman, Robert; Hensen, Emiel J. M.

doi:10.1002/cctc.201701203

Cited by 47 publications

(48 citation statements)

References 36 publications

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“…58 By combining 12 C 16 O/ 13 C 18 O isotopic scrambling with in situ infrared spectroscopy, we have demonstrated earlier that direct CO dissociation proceeds predominantly on step-edge sites. 37 This is consistent with the expected strong structure sensitivity of the CO dissociation reaction.…”

Section: Discussionsupporting

confidence: 87%

“…The detailed preparation of this catalyst can be found in the literature. 37 The accessible surface area of 116.7 μmol of Co atoms/g of catalyst was determined by H 2 -chemisorption (ASAP 2010, Micromeritics). The average cobalt particle size of 15 nm was determined by TEM analysis (FEI Tecnai 20) and confirmed by in situ XRD (D/max-2600, Rigaku).…”

Section: Methodsmentioning

confidence: 99%

“…We have previously shown that CO disproportionation via the Boudouard reaction is a structure-sensitive reaction. 37 It occurs at a high rate in the absence of H 2 but suffers from rapid deactivation due to the buildup of carbon. In the present work, we characterize in more detail the carbon species deposited during the Boudouard reaction and their propensity toward hydrogenation.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Carbon Deposits on the Cobalt-Catalyzed Fischer–Tropsch Reaction: Evidence of a Two-Site Reaction Model

et al. 2018

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One of the well-known observations in the Fischer–Tropsch (FT) reaction is that the CH4 selectivity for cobalt catalysts is always higher than the value expected on the basis of the Anderson–Schulz–Flory (ASF) distribution. Depositing graphitic carbon on a cobalt catalyst strongly suppresses this non-ASF CH4, while the formation of higher hydrocarbons is much less affected. Carbon was laid down on the cobalt catalyst via the Boudouard reaction. We provide evidence that the amorphous carbon does not influence the FT reaction, as it can be easily hydrogenated under reaction conditions. Graphitic carbon is rapidly formed and cannot be removed. This unreactive form of carbon is located on terrace sites and mainly decreases the CO conversion by limiting CH4 formation. Despite nearly unchanged higher hydrocarbon yield, the presence of graphitic carbon enhances the chain-growth probability and strongly suppresses olefin hydrogenation. We demonstrate that graphitic carbon will slowly deposit on the cobalt catalysts during CO hydrogenation, thereby influencing CO conversion and the FT product distribution in a way similar to that for predeposited graphitic carbon. We also demonstrate that the buildup of graphitic carbon by 13CO increases the rate of C–C coupling during the 12C3H6 hydrogenation reaction, whose products follow an ASF-type product distribution of the FT reaction. We explain these results by a two-site model on the basis of insights into structure sensitivity of the underlying reaction steps in the FT mechanism: carbon formed on step-edge sites is involved in chain growth or can migrate to terrace sites, where it is rapidly hydrogenated to CH4. The primary olefinic FT products are predominantly hydrogenated on terrace sites. Covering the terraces by graphitic carbon increases the residence time of CHx intermediates, in line with decreased CH4 selectivity and increased chain-growth rate.

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Section: Discussionsupporting

confidence: 87%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Influence of Carbon Deposits on the Cobalt-Catalyzed Fischer–Tropsch Reaction: Evidence of a Two-Site Reaction Model

et al. 2018

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“…As outlined above, we have demonstrated that direct CO dissociation on the same Co/SiO 2 catalyst is possible and can be correlated to a minority site at the surface. 53 Therefore, the minor increase in CO coverage will significantly influence the reaction kinetics. This scenario will be discussed in a companion paper.…”

Section: Resultsmentioning

confidence: 99%

“…30,48−52 Although it is difficult to disprove an H-assisted CO dissociation mechanism on a surface that contains adsorbed CO and H, we have recently demonstrated by isotopic exchange of a 12 C 16 O/ 13 C 18 O mixture that CO dissociation is fast and reversible on an empty cobalt surface. 53 …”

Section: Introductionmentioning

confidence: 99%

Mechanism of Cobalt-Catalyzed CO Hydrogenation: 1. Methanation

et al. 2017

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The mechanism of CO hydrogenation to CH4 at 260 °C on a cobalt catalyst is investigated using steady-state isotopic transient kinetic analysis (SSITKA) and backward and forward chemical transient kinetic analysis (CTKA). The dependence of CHx residence time is determined by 12CO/H2 → 13CO/H2 SSITKA as a function of the CO and H2 partial pressure and shows that the CH4 formation rate is mainly controlled by CHx hydrogenation rather than CO dissociation. Backward CO/H2 → H2 CTKA emphasizes the importance of H coverage on the slow CHx hydrogenation step. The H coverage strongly depends on the CO coverage, which is directly related to CO partial pressure. Combining SSITKA and backward CTKA allows determining that the amount of additional CH4 obtained during CTKA is nearly equal to the amount of CO adsorbed to the cobalt surface. Thus, under the given conditions overall barrier for CO hydrogenation to CH4 under methanation condition is lower than the CO adsorption energy. Forward CTKA measurements reveal that O hydrogenation to H2O is also a relatively slow step compared to CO dissociation. The combined transient kinetic data are used to fit an explicit microkinetic model for the methanation reaction. The mechanism involving direct CO dissociation represents the data better than a mechanism in which H-assisted CO dissociation is assumed. Microkinetics simulations based on the fitted parameters confirms that under methanation conditions the overall CO consumption rate is mainly controlled by C hydrogenation and to a smaller degree by O hydrogenation and CO dissociation. These simulations are also used to explore the influence of CO and H2 partial pressure on possible rate-controlling steps.

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Ceria‐Supported Cobalt Catalyst for Low‐Temperature Methanation at Low Partial Pressures of CO₂

et al. 2022

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The direct catalytic conversion of atmospheric CO 2 to valuable chemicals is a promising solution to avert negative consequences of rising CO 2 concentration. However, heterogeneous catalysts efficient at low partial pressures of CO 2 still need to be developed. Here, we explore Co/CeO 2 as a catalyst for the methanation of diluted CO 2 streams. This material displays an excellent performance at reaction temperatures as low as 175 °C and CO 2 partial pressures as low as 0.4 mbar (the atmospheric CO 2 concentration). To gain mechanistic understanding of this unusual activity, we employed in situ X-ray photoelectron spectroscopy and operando infrared spectroscopy. The higher surface concentration and reactivity of formates and carbonyls -key reaction intermediates-explain the superior activity of Co/CeO 2 as compared to a conventional Co/ SiO 2 catalyst. This work emphasizes the catalytic role of the cobalt-ceria interface and will aid in developing more efficient CO 2 hydrogenation catalysts.

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Mechanism of Carbon Monoxide Dissociation on a Cobalt Fischer–Tropsch Catalyst

Cited by 47 publications

References 36 publications

Influence of Carbon Deposits on the Cobalt-Catalyzed Fischer–Tropsch Reaction: Evidence of a Two-Site Reaction Model

Influence of Carbon Deposits on the Cobalt-Catalyzed Fischer–Tropsch Reaction: Evidence of a Two-Site Reaction Model

Mechanism of Cobalt-Catalyzed CO Hydrogenation: 1. Methanation

Ceria‐Supported Cobalt Catalyst for Low‐Temperature Methanation at Low Partial Pressures of CO₂

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Mechanism of Carbon Monoxide Dissociation on a Cobalt Fischer–Tropsch Catalyst

Cited by 47 publications

References 36 publications

Influence of Carbon Deposits on the Cobalt-Catalyzed Fischer–Tropsch Reaction: Evidence of a Two-Site Reaction Model

Influence of Carbon Deposits on the Cobalt-Catalyzed Fischer–Tropsch Reaction: Evidence of a Two-Site Reaction Model

Mechanism of Cobalt-Catalyzed CO Hydrogenation: 1. Methanation

Ceria‐Supported Cobalt Catalyst for Low‐Temperature Methanation at Low Partial Pressures of CO2

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Ceria‐Supported Cobalt Catalyst for Low‐Temperature Methanation at Low Partial Pressures of CO₂