Understanding reaction-induced restructuring of well-defined FexOyCz compositions and its effect on CO2 hydrogenation

Skrypnik, Andrey S.; Yang, Qingxin; Матвиенко, А. А.; Bychkov, V. Yu.; Tulenin, Yuriy P.; Lund, Henrik; Petrov, Sergey A.; Kraehnert, Ralph; Arinchtein, Aleks; Weiß, Jana; Brueckner, Angelika; Kondratenko, Evgenii V.

doi:10.1016/j.apcatb.2021.120121

Cited by 38 publications

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“…In general, Fe 3 O 4 and Fe 5 C 2 are the main phases on spent catalysts (22,23). Skrypnik et al (24) investigated the steady-state composition of Fe x O y C z catalysts (mixture of -Fe, iron carbides, and oxides) along the catalyst bed, which suggests that Fe 3 O 4 , FeO, and Fe are converted into iron carbides under reaction conditions. Zhao et al (25) developed an Fe 2 N@C catalyst for selective CO 2 hydrogenation to hydrocarbons and found that iron nitrides are in situ converted to highly active iron carbides.…”

Section: Introductionmentioning

confidence: 99%

Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO ₂ hydrogenation

et al. 2022

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Identifying the dynamic structure of heterogeneous catalysts is crucial for the rational design of new ones. In this contribution, the structural evolution of Fe(0) catalysts during CO 2 hydrogenation to hydrocarbons has been investigated by using several (quasi) in situ techniques. Upon initial reduction, Fe species are carburized to Fe 3 C and then to Fe 5 C 2 . The by-product of CO 2 hydrogenation, H 2 O, oxidizes the iron carbide to Fe 3 O 4 . The formation of Fe 3 O 4 @(Fe 5 C 2 +Fe 3 O 4 ) core-shell structure was observed at steady state, and the surface composition depends on the balance of oxidation and carburization, where water plays a key role in the oxidation. The performance of CO 2 hydrogenation was also correlated with the dynamic surface structure. Theoretical calculations and controll experiments reveal the interdependence between the phase transition and reactive environment. We also suggest a practical way to tune the competitive reactions to maintain an Fe 5 C 2 -rich surface for a desired C 2+ productivity.

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Section: Introductionmentioning

confidence: 99%

Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO ₂ hydrogenation

et al. 2022

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“…The reaction has been reported to proceed in two steps: the reverse water gas shift reaction (RWGS), which reduces CO 2 to CO, and a subsequent hydrogenation of CO, i.e., a typical CO Fischer-Tropsch synthesis (CO-FTS). Iron-based catalysts, such as hematite (α-Fe 2 O 3 ), are able to catalyze both reactions under similar reaction conditions and show high selectivities toward higher hydrocarbons [6][7][8]. Therefore, it is of great importance to develop stable and highly efficient iron-based CO 2 -FTS catalysts.…”

Section: Introductionmentioning

confidence: 99%

“…α-Fe 2 O 3 , a typical starting material, can be converted under the employed reducing conditions into many different phases under the conditions of the CO 2 -FTS-such as wustite (FeO), maghemite (γ-Fe 2 O 3 ), magnetite (Fe 3 O 4 ), elemental iron (Fe), and iron carbides. Each of these phases may potentially form species which affect both activity and selectivity of the catalyst [8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

“…Nonetheless, understanding the carbide formation process under the CO 2 -FTS reaction conditions still remains a challenge. Iron oxides can show various crystal structures and different phases, which, accordingly, obstruct clear conclusions due to the heterogeneity of the studied catalysts [8,9]. Moreover, these materials are sensitive to changes in temperature, time on stream, applied pressure, humidity, gases (air, H 2 , CO, CO 2 ) during CO 2 -FTS [6][7][8].…”

Section: Introductionmentioning

confidence: 99%

“…Iron oxides can show various crystal structures and different phases, which, accordingly, obstruct clear conclusions due to the heterogeneity of the studied catalysts [8,9]. Moreover, these materials are sensitive to changes in temperature, time on stream, applied pressure, humidity, gases (air, H 2 , CO, CO 2 ) during CO 2 -FTS [6][7][8]. Beyond that, rather low crystallinities of the intermediate phases and complex nature of the surface species on iron-based catalysts in CO 2 -FTS process make a clear identification of the carbide phases among other possible intermediate phases difficult.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Phase Composition and Pretreatment on the Conversion of Iron Oxides into Iron Carbides in Syngas Atmospheres

Arinchtein

Geske

et al. 2021

Catalysts

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CO2 Fischer–Tropsch synthesis (CO2–FTS) is a promising technology enabling conversion of CO2 into valuable chemical feedstocks via hydrogenation. Iron–based CO2–FTS catalysts are known for their high activities and selectivities towards the formation of higher hydrocarbons. Importantly, iron carbides are the presumed active phase strongly associated with the formation of higher hydrocarbons. Yet, many factors such as reaction temperature, atmosphere, and pressure can lead to complex transformations between different oxide and/or carbide phases, which, in turn, alter selectivity. Thus, understanding the mechanism and kinetics of carbide formation remains challenging. We propose model–type iron oxide films of controlled nanostructure and phase composition as model materials to study carbide formation in syngas atmospheres. In the present work, different iron oxide precursor films with controlled phase composition (hematite, ferrihydrite, maghemite, maghemite/magnetite) and ordered mesoporosity are synthesized using the evaporation–induced self–assembly (EISA) approach. The model materials are then exposed to a controlled atmosphere of CO/H2 at 300 °C. Physicochemical analysis of the treated materials indicates that all oxides convert into carbides with a core–shell structure. The structure appears to consist of crystalline carbide cores surrounded by a partially oxidized carbide shell of low crystallinity. Larger crystallites in the original iron oxide result in larger carbide cores. The presented simple route for the synthesis and analysis of soft–templated iron carbide films will enable the elucidation of the dynamics of the oxide to carbide transformation in future work.

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Bestimmung von Performance‐Deskriptoren für die CO₂‐Hydrierung an alkalimetallpromotierten Katalysatoren auf Eisenbasis

et al. 2022

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Alkalimetallpromotoren werden in großem Umfang für die Herstellung heterogener Katalysatoren eingesetzt, die in vielen industriell wichtigen Reaktionen verwendet werden. Die Ursachen für ihre Wirkung sind jedoch in der Regel nur schwer zu ergründen. In dieser Arbeit werden die mechanistischen und kinetischen Aspekte der Wirkung von Alkalimetallen bei der CO 2 -Hydrierung an Fe-haltigen Katalysatoren mithilfe modernster Charakterisierungstechniken sowie räumlich aufgelöster stationärer und instationärer kinetischer Analysen aufgeklärt. Die Promotoren beeinflussen die elektronischen Eigenschaften von Eisen in Eisenkarbiden. Diese Karbideigenschaften bestimmen die Fähigkeit des Katalysators, H 2 , CO und CO 2 zu aktivieren. Die Elektronegativität des Alkalimetallpromoters nach der Allen-Skala wurde erfolgreich mit der Reaktionsgeschwindigkeit der CO 2 -Hydrierung zu höheren Kohlenwasserstoffen und CH 4 sowie mit den Geschwindigkeitskonstanten der einzelnen Schritte der CO-oder CO 2 -Aktivierung korreliert. Die gewonnenen Erkenntnisse können für die Entwicklung und Herstellung von Katalysatoren für andere Reaktionen, bei welchen derartige Promotoren ebenfalls verwendet werden, von Nutzen sein.

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Understanding reaction-induced restructuring of well-defined FexOyCz compositions and its effect on CO2 hydrogenation

Cited by 38 publications

References 41 publications

Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO ₂ hydrogenation

Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO ₂ hydrogenation

Influence of Phase Composition and Pretreatment on the Conversion of Iron Oxides into Iron Carbides in Syngas Atmospheres

Bestimmung von Performance‐Deskriptoren für die CO₂‐Hydrierung an alkalimetallpromotierten Katalysatoren auf Eisenbasis

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Understanding reaction-induced restructuring of well-defined FexOyCz compositions and its effect on CO2 hydrogenation

Cited by 38 publications

References 41 publications

Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO 2 hydrogenation

Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO 2 hydrogenation

Influence of Phase Composition and Pretreatment on the Conversion of Iron Oxides into Iron Carbides in Syngas Atmospheres

Bestimmung von Performance‐Deskriptoren für die CO2‐Hydrierung an alkalimetallpromotierten Katalysatoren auf Eisenbasis

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Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO ₂ hydrogenation

Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO ₂ hydrogenation

Bestimmung von Performance‐Deskriptoren für die CO₂‐Hydrierung an alkalimetallpromotierten Katalysatoren auf Eisenbasis