In-situ high temparature X-ray diffraction studies of nanocrystalline iron carbides

Sethuraman, Anantha R.

doi:10.1016/0965-9773(94)90130-9

Cited by 4 publications

(7 citation statements)

References 14 publications

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“…O atom free θ-Fe C phase can survive up to~400-500°C before decomposing directly to α-Fe and C atoms. [173] To conclude, the formation of the θ-Fe C phase does not follow the same route as for the ɛ-Fe 3 C, η-Fe C, χ-Fe 5 C 2 or θ-Fe C phases, but might have its own formation route. Nevertheless, θ-Fe 7 C 3 phase formation is possible under relatively mild and FTS reaction relevant conditions, although more systematic research is needed on its formation specifics.…”

Section: Fe Carbide Phasementioning

confidence: 87%

“…In literature, the θ-Fe 7 C 3 phase is either observed to form at extreme conditions, such as at 60 kbar with > 1100°C from a mixture of graphite and α-Fe, [172] or via laser pyrolysis of Fe(CO) 5 under C 2 H 2/4 . [157,160,173] A more interesting case for the FTS reaction related discussion in the realm of θ-Fe 7 C 3 formation is observed in a study by Tajima and Hirano, where Ba-promoted Fe 3 O 4 was carburized with pure CO at unspecified reaction pressure. [174] Within the temperature range of 300-375°C, the Ba-Fe 3 O 4 carburized into a mixture of the χ-Fe 5 C 2 and θ-Fe 7 C 3 phases.…”

Section: Fe Carbide Phasementioning

confidence: 99%

“…Regarding the θ-Fe 7 C 3 phase thermal stability, a heat treatment of the θ-Fe 7 C 3 phase under He leads to the phase's decomposition, with decomposition temperature depending on the O atom impurity content in the θ-Fe 7 C 3 crystal lattice. [173] High O atom impurity content causes the θ-Fe 7 C 3 phase to decompose to Fe oxides and α-Fe between 300-400°C. O atom free θ-Fe C phase can survive up to~400-500°C before decomposing directly to α-Fe and C atoms.…”

Section: Fe Carbide Phasementioning

confidence: 99%

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Carbon Pathways, Sodium‐Sulphur Promotion and Identification of Iron Carbides in Iron‐based Fischer‐Tropsch Synthesis

Paalanen

Weckhuysen

2020

ChemCatChem

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Fisher‐Tropsch Synthesis (FTS) is industrially used for converting a carbon‐containing feedstock, such as coal, natural gas, biomass, and municipal waste, via the production of synthesis gas (a mixture of CO+H2) into hydrocarbons. This review article focuses on Fe‐based FTS catalysis, thereby focusing on the process conditions available for steering the various carbon pathways from input CO and their associated reactions. We will also discuss the effects of alkali‐sulphur chemical promotion and the identification of the FTS reaction active Fe carbides, which are assigned with precise crystal structures and nomenclature. Each observed Fe carbide crystal structure is further assigned with corresponding Mössbauer Absorption Spectroscopy (MAS) hyperfine fields. The expected formation temperatures and experimental conditions for the identified Fe carbides encountered in FTS research, namely ϵ‐Fe3C, η‐Fe2C, χ‐Fe5C2, θ‐Fe3C and θ‐Fe7C3, are reviewed.

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Section: Fe Carbide Phasementioning

confidence: 87%

Section: Fe Carbide Phasementioning

confidence: 99%

Section: Fe Carbide Phasementioning

confidence: 99%

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Carbon Pathways, Sodium‐Sulphur Promotion and Identification of Iron Carbides in Iron‐based Fischer‐Tropsch Synthesis

Paalanen

Weckhuysen

2020

ChemCatChem

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“…catalyst materials. The θ-Fe 7 C 3 phase can be formed under rather extreme conditions, [91][92][93][94] but may also form under milder FTS reaction conditions, which are more relevant to the present discussion. [20,28,95] In order to form the θ-Fe 7 C 3 phase under mild conditions, Tajima and Hirano used a Ba-promoted Fe 3 O 4 carburized with pure CO under unspecified pressure at 300-375°C.…”

Section: Formation Of the θ-Fe 7 C 3 Phasementioning

confidence: 99%

“…[94] An oxygenfree θ-Fe 7 C 3 phase has been witnessed to survive temperatures up to � 400-500°C before decomposing into α-Fe and C atoms. [94] Figure 5a-b shows that the experimental MAS and XRPD based R-QPA quantifications are very much in line with each other and the R-QPA fittings to the measured diffractograms correspond well with the employed Fe carbide crystal structures, as can be seen in Figure 2 for UP and in Figure 3 for NaÀ S catalysts. It is therefore safe to conclude that the earlier identification and proposed nomenclature for the Fe carbides followed here is a reasonable one.…”

Section: Formation Of the θ-Fe 7 C 3 Phasementioning

confidence: 99%

Identification of Iron Carbides in Fe(−Na−S)/α‐Al₂O₃ Fischer‐Tropsch Synthesis Catalysts with X‐ray Powder Diffractometry and Mössbauer Absorption Spectroscopy

et al. 2020

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In Fe-based Fischer-Tropsch Synthesis (FTS), the Fe carbides form under the carburizing H 2 : CO reaction atmosphere providing the active phases for hydrocarbon synthesis. H 2 reduced Fe (À NaÀ S)/α-Al 2 O 3 catalyst materials, with and without NaÀ S promotion, were carburized under CO at 240-440°C to form Fe carbides. X-ray Powder Diffractometry (XRPD) with Rietveld Quantitative Phase Analysis (R-QPA) and Mössbauer Absorption Spectroscopy (MAS) were used to identity and quantify the formed Fe carbide phases. The Fe carbides formed in order of increasing temperature are ɛ-Fe 3 C, η-Fe 2 C, χ-Fe 5 C 2 and θ-Fe 3 C. θ-Fe 7 C 3 and a distorted χ-Fe 5 C 2 phase are formed at 25 bar CO (340°C) from a Fe oxide precursor. Fe carbide formation was unaffected by NaÀ S addition, but it did increase Fe oxidation (� 290°C) and preferred formation of χ-Fe 5 C 2 over θ-Fe 3 C phase (� 390°C). The results unify the often ambiguous Fe carbide identification and nomenclature and specify the role of NaÀ S in the carburization process.

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Surface Composition of Carbon Nanotubes-Fe-Alumina Nanocomposite Powders: An Integral Low-Energy Electron Mössbauer Spectroscopic Study

et al. 2008

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The surface state of carbon nanotubes-Fe-alumina nanocomposite powders was studied by transmission and integral low-energy electron Mössbauer spectroscopy. Several samples, prepared under reduction of the R-Al 1.8-Fe 0.2 O 3 precursor in a H 2-CH 4 atmosphere applying the same heating and cooling rate and changing only the maximum temperature (800-1070°C) were investigated, demonstrating that integral low-energy electron Mössbauer spectroscopy is a promising tool complementing transmission Mössbauer spectroscopy for the investigation of the location of the metal Fe and iron-carbide particles in the different carbon nanotubenanocomposite systems containing iron. The nature of the iron species (Fe 3+ , Fe 3 C , R-Fe, γ-Fe-C) is correlated to their location in the material. In particular, much information was derived for the powders prepared by using a moderate reduction temperature (800, 850, and 910°C), for which the transmission and integral low-energy electron Mössbauer spectra are markedly different. Indeed, R-Fe and Fe 3 C were not observed as surface species, while γ-Fe-C is present at the surface and in the bulk in the same proportion independent of the temperature of preparation. This could show that most of the nanoparticles (detected as Fe 3 C and/or γ-Fe-C) that contribute to the formation of carbon nanotubes are located in the outer porosity of the material, as opposed to the topmost (ca. 5 nm) surface. For the higher reduction temperatures T r of 990°C and 1070°C, all Fe and Fe-carbide particles formed during the reduction are distributed evenly in the bulk and the surface of the matrix grains. The integral low-energy electron Mössbauer spectroscopic study of a powder oxidized in air at 600°C suggests that all Fe 3 C particles oxidize to R-Fe 2 O 3 , while the R-Fe and/or γ-Fe-C are partly transformed to Fe 1-x O and R-Fe 2 O 3 , the latter phase forming a protecting layer that prevents total oxidation.

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In-situ high temparature X-ray diffraction studies of nanocrystalline iron carbides

Cited by 4 publications

References 14 publications

Carbon Pathways, Sodium‐Sulphur Promotion and Identification of Iron Carbides in Iron‐based Fischer‐Tropsch Synthesis

Carbon Pathways, Sodium‐Sulphur Promotion and Identification of Iron Carbides in Iron‐based Fischer‐Tropsch Synthesis

Identification of Iron Carbides in Fe(−Na−S)/α‐Al₂O₃ Fischer‐Tropsch Synthesis Catalysts with X‐ray Powder Diffractometry and Mössbauer Absorption Spectroscopy

Surface Composition of Carbon Nanotubes-Fe-Alumina Nanocomposite Powders: An Integral Low-Energy Electron Mössbauer Spectroscopic Study

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In-situ high temparature X-ray diffraction studies of nanocrystalline iron carbides

Cited by 4 publications

References 14 publications

Carbon Pathways, Sodium‐Sulphur Promotion and Identification of Iron Carbides in Iron‐based Fischer‐Tropsch Synthesis

Carbon Pathways, Sodium‐Sulphur Promotion and Identification of Iron Carbides in Iron‐based Fischer‐Tropsch Synthesis

Identification of Iron Carbides in Fe(−Na−S)/α‐Al2O3 Fischer‐Tropsch Synthesis Catalysts with X‐ray Powder Diffractometry and Mössbauer Absorption Spectroscopy

Surface Composition of Carbon Nanotubes-Fe-Alumina Nanocomposite Powders: An Integral Low-Energy Electron Mössbauer Spectroscopic Study

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Identification of Iron Carbides in Fe(−Na−S)/α‐Al₂O₃ Fischer‐Tropsch Synthesis Catalysts with X‐ray Powder Diffractometry and Mössbauer Absorption Spectroscopy