On the link between CO surface coverage and selectivity to CH4 during CO2 hydrogenation over supported cobalt catalysts

Bredy, Pauline; Farrusseng, David; Schuurman, Y.; Meunier, Frédéric

doi:10.1016/j.jcat.2022.05.001

Cited by 18 publications

(13 citation statements)

References 21 publications

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“…One possibility is incomplete reduction of the carbide surface due to ligand retention, which is supported by the low initial activity and long induction period described above. Additionally, the lack of CO* site density but moderate H* site density suggests that another possibility for the high methane selectivity for the OAm-MoC 1– x /C catalyst is a comparatively high H*/CO x * ratio on this catalyst surface after the induction period, leading to complete hydrogenation to methane. − In contrast, the t -BuNH 2 –MoC 1– x /C catalyst reduced at 250 °C exhibited greater CO* site density with a H* site density in the same order-of-magnitude, suggesting a lower H*/CO x * ratio, and subsequently, a lower hydrogenation selectivity to CH 4 . Comparing the selectivity for the t -BuNH 2 -MoC 1– x /C catalyst reduced at 250 °C to both catalysts pretreated at 450 °C revealed similar product slates (Figure S8).…”

Section: Resultsmentioning

confidence: 99%

Activating Molybdenum Carbide Nanoparticle Catalysts under Mild Conditions Using Thermally Labile Ligands

Karadaghi

Habas

et al. 2022

Chem. Mater.

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Transition-metal carbides are promising low-cost materials for various catalytic transformations due to their multifunctionality and noble-metal-like behavior. Nanostructuring transition-metal carbides offers advantages resulting from the large surface-area-to-volume ratios inherent in colloidal nanoparticle catalysts; however, a barrier for their utilization is removal of the long-chain aliphatic ligands on their surface to access active sites. Annealing procedures to remove these ligands require temperatures greater than the catalyst synthesis and catalytic reaction temperatures and may further result in coking or particle sintering that can reduce catalytic performance. One way to circumvent this problem is by replacing the long-chain aliphatic ligands with smaller ligands that can be easily removed through low-temperature thermolytic decomposition. Here, we present the exchange of native oleylamine ligands on colloidal α-MoC1–x nanoparticles for thermally labile tert-butylamine ligands. Analyses of the ligand exchange reaction by solution 1H NMR spectroscopy, FT-IR spectroscopy, and thermogravimetric analysis–mass spectrometry (TGA-MS) confirm the displacement of 60% of the native oleylamine ligands for the thermally labile tert-butylamine, which can be removed with a mild activation step at 250 °C. Catalytic site densities were determined by carbon monoxide (CO) chemisorption, demonstrating that the mild thermal treatment at 250 °C activates ca. 25% of the total binding sites, while the native oleylamine-terminated MoC1–x nanoparticles showed no available surface binding sites after this low-temperature treatment. The mild pretreatment at 250 °C also shows distinctly different initial activities and postinduction period selectivities in the CO2 hydrogenation reaction for the ligand exchanged MoC1–x nanoparticle catalysts and the as-prepared material.

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Section: Resultsmentioning

confidence: 99%

Activating Molybdenum Carbide Nanoparticle Catalysts under Mild Conditions Using Thermally Labile Ligands

Karadaghi

Habas

et al. 2022

Chem. Mater.

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“…Operando DRIFTS experiments were performed on a modified high-temperature DRIFT cell (from Spectra-Tech, Hong Kong) fitted with CaF 2 windows using a Collector II assembly. A description and properties of the cell can be found in earlier references [28][29][30]. The spectrophotometer used was a Nicolet 8700 (ThermoFischer Scientific, Waltham, MA, USA) fitted with a liquid-N 2 cooled MCT detector.…”

Section: Methodsmentioning

confidence: 99%

Differentiating the Reactivity of ZrO2-Bound Formates Formed on Cu/ZrO2 during CO2 Hydrogenation

et al. 2022

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The surface species formed during the hydrogenation of CO2 with H2 over a ZrO2-supported Cu catalyst were investigated by operando diffuse reflectance FT-IR spectroscopy at 220 °C and 3 bar. The reactivity of two different formates located on zirconia could be unraveled. The data pointed to ZrO2 hydroxyl groups at 3755 cm−1 as the sites on which carbonates and then formates were hydrogenated to methoxy species. Formate hydrogenation appeared as the slowest step. The most reactive ZrO2-bound formates exhibited a rate constant of reaction about 65 times higher than that of the slower formate.

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“…Using operando IR spectroscopy, they found that the selectivity toward methane is related to the CO* coverage. 410 When shifting from a CO-rich to a CO 2 -rich feed, the CO* coverage decreases and methane selectivity increases. A possible explanation for the increased methane yield is the higher H* coverage when CO* coverage decreases.…”

Section: Co-and Ru-based Co 2 -Ftsmentioning

confidence: 99%

“…On cobalt, high CO partial pressures are necessary to induce chain growth, as shown by DFT calculations by the Saeys group and the Iglesia group and experiments by the Meunier group and the Weststrate group. ,,, While the groups of Iglesia and Saeys mainly focused on CO-FT, the group of Meunier investigated the surface of the cobalt catalysts under CO 2 hydrogenation conditions. Using operando IR spectroscopy, they found that the selectivity toward methane is related to the CO* coverage . When shifting from a CO-rich to a CO 2 -rich feed, the CO* coverage decreases and methane selectivity increases.…”

Section: Co2-fts: Revival Of the Century-old Fischer–tropsch Process?mentioning

confidence: 99%

Molecular Views on Fischer–Tropsch Synthesis

Rommens

Saeys

2023

Chem. Rev.

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For nearly a century, the Fischer–Tropsch (FT) reaction has been subject of intense debate. Various molecular views on the active sites and on the reaction mechanism have been presented for both Co- and Fe-based FT reactions. In the last 15 years, the emergence of a surface-science- and molecular-modeling-based bottom-up approach has brought this molecular picture a step closer. Theoretical models provided a structural picture of the Co catalyst particles. Recent surface science experiments and density functional theory (DFT) calculations highlighted the importance of realistic surface coverages, which can induce surface reconstruction and impact the stability of reaction intermediates. For Co-based FTS, detailed microkinetic simulations and mechanistic experiments are moving toward a consensus about the active sites and the reaction mechanism. The dynamic phase evolution of Fe-based catalysts under the reaction conditions complicates identification of the surface structure and the active sites. New techniques can help tackle the combinatorial complexity in these systems. Experimental and DFT studies have addressed the mechanism for Fe-based catalysts; the absence of a clear molecular picture of the active sites, however, limits the development of a molecular view of the mechanism. Finally, direct CO2 hydrogenation to long-chain hydrocarbons could present a sustainable pathway for FT synthesis.

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On the link between CO surface coverage and selectivity to CH4 during CO2 hydrogenation over supported cobalt catalysts

Cited by 18 publications

References 21 publications

Activating Molybdenum Carbide Nanoparticle Catalysts under Mild Conditions Using Thermally Labile Ligands

Activating Molybdenum Carbide Nanoparticle Catalysts under Mild Conditions Using Thermally Labile Ligands

Differentiating the Reactivity of ZrO2-Bound Formates Formed on Cu/ZrO2 during CO2 Hydrogenation

Molecular Views on Fischer–Tropsch Synthesis

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