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

Pasi P. Paalanen; Sophie H. van Vreeswijk; A. Iulian Dugulan; Bert M. Weckhuysen

doi:10.1002/cctc.202000707

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

Pasi P. Paalanen, Sophie H. van Vreeswijk, A. Iulian Dugulan, Bert M. Weckhuysen^*

^*Corresponding author for this work

Delft University of Technology

Research output: Contribution to journal › Article › Academic › peer-review

Abstract

In Fe-based Fischer-Tropsch Synthesis (FTS), the Fe carbides form under the carburizing H₂ : CO reaction atmosphere providing the active phases for hydrocarbon synthesis. H₂ reduced Fe(−Na−S)/α-Al₂O₃ catalyst materials, with and without Na−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 ϵ-Fe₃C, η-Fe₂C, χ-Fe₅C₂ and θ-Fe₃C. θ-Fe₇C₃ and a distorted χ-Fe₅C₂ phase are formed at 25 bar CO (340 °C) from a Fe oxide precursor. Fe carbide formation was unaffected by Na−S addition, but it did increase Fe oxidation (≤290 °C) and preferred formation of χ-Fe₅C₂ over θ-Fe₃C phase (≥390 °C). The results unify the often ambiguous Fe carbide identification and nomenclature and specify the role of Na−S in the carburization process.

Original language	English
Pages (from-to)	5121-5139
Number of pages	19
Journal	ChemCatChem
Volume	12
Issue number	20
DOIs	https://doi.org/10.1002/cctc.202000707
Publication status	Published - 20 Oct 2020

Funding

This research received funding from the Netherlands Research Council (NWO) in the framework of the TASC Technology Area “Syngas, a Switch to Flexible New feedstock for the Chemical Industry (TA‐Syngas)”. Dow and Johnson‐Matthey are also acknowledged for their funding and support. H. C. de Waard and C. Mulder (GeoLab at Universiteit Utrecht, UU) and Mikrolab Kolbe (Oberhausen, Germany) are acknowledged for the ICP‐OES measurements, while M. Versluijs‐Helder (UU) is thanked for the TGA‐MS measurements. J. D. Meeldijk (UU) and C. W. T. M. Schneijdenberg (UU) are acknowledged for their guidance in taking the TEM images. Use of VESTA software is acknowledged in visualization of the Fe carbide crystal structures in the graphical abstract.

Keywords

Fischer-Tropsch Synthesis
Iron Carbides
Mössbauer Absorption Spectroscopy
Na−S Promotion
Rietveld Quantitative Phase Analysis
X-ray Powder Diffractometry

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Cite this

@article{4866b82922d24354b7f50b9dc761641e,

title = "Identification of Iron Carbides in Fe(−Na−S)/α-Al2O3 Fischer-Tropsch Synthesis Catalysts with X-ray Powder Diffractometry and M{\"o}ssbauer Absorption Spectroscopy",

abstract = "In Fe-based Fischer-Tropsch Synthesis (FTS), the Fe carbides form under the carburizing H2 : CO reaction atmosphere providing the active phases for hydrocarbon synthesis. H2 reduced Fe(−Na−S)/α-Al2O3 catalyst materials, with and without Na−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 M{\"o}ssbauer Absorption Spectroscopy (MAS) were used to identity and quantify the formed Fe carbide phases. The Fe carbides formed in order of increasing temperature are ϵ-Fe3C, η-Fe2C, χ-Fe5C2 and θ-Fe3C. θ-Fe7C3 and a distorted χ-Fe5C2 phase are formed at 25 bar CO (340 °C) from a Fe oxide precursor. Fe carbide formation was unaffected by Na−S addition, but it did increase Fe oxidation (≤290 °C) and preferred formation of χ-Fe5C2 over θ-Fe3C phase (≥390 °C). The results unify the often ambiguous Fe carbide identification and nomenclature and specify the role of Na−S in the carburization process.",

keywords = "Fischer-Tropsch Synthesis, Iron Carbides, M{\"o}ssbauer Absorption Spectroscopy, Na−S Promotion, Rietveld Quantitative Phase Analysis, X-ray Powder Diffractometry",

author = "Paalanen, {Pasi P.} and {van Vreeswijk}, {Sophie H.} and Dugulan, {A. Iulian} and Weckhuysen, {Bert M.}",

year = "2020",

month = oct,

day = "20",

doi = "10.1002/cctc.202000707",

language = "English",

volume = "12",

pages = "5121--5139",

journal = "ChemCatChem",

issn = "1867-3880",

publisher = "Wiley - VCH Verlag GmbH & CO. KGaA",

number = "20",

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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. / Paalanen, Pasi P.; van Vreeswijk, Sophie H.; Dugulan, A. Iulian et al.
In: ChemCatChem, Vol. 12, No. 20, 20.10.2020, p. 5121-5139.

Research output: Contribution to journal › Article › Academic › peer-review

TY - JOUR

T1 - Identification of Iron Carbides in Fe(−Na−S)/α-Al2O3 Fischer-Tropsch Synthesis Catalysts with X-ray Powder Diffractometry and Mössbauer Absorption Spectroscopy

AU - Paalanen, Pasi P.

AU - van Vreeswijk, Sophie H.

AU - Dugulan, A. Iulian

AU - Weckhuysen, Bert M.

PY - 2020/10/20

Y1 - 2020/10/20

N2 - In Fe-based Fischer-Tropsch Synthesis (FTS), the Fe carbides form under the carburizing H2 : CO reaction atmosphere providing the active phases for hydrocarbon synthesis. H2 reduced Fe(−Na−S)/α-Al2O3 catalyst materials, with and without Na−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 ϵ-Fe3C, η-Fe2C, χ-Fe5C2 and θ-Fe3C. θ-Fe7C3 and a distorted χ-Fe5C2 phase are formed at 25 bar CO (340 °C) from a Fe oxide precursor. Fe carbide formation was unaffected by Na−S addition, but it did increase Fe oxidation (≤290 °C) and preferred formation of χ-Fe5C2 over θ-Fe3C phase (≥390 °C). The results unify the often ambiguous Fe carbide identification and nomenclature and specify the role of Na−S in the carburization process.

AB - In Fe-based Fischer-Tropsch Synthesis (FTS), the Fe carbides form under the carburizing H2 : CO reaction atmosphere providing the active phases for hydrocarbon synthesis. H2 reduced Fe(−Na−S)/α-Al2O3 catalyst materials, with and without Na−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 ϵ-Fe3C, η-Fe2C, χ-Fe5C2 and θ-Fe3C. θ-Fe7C3 and a distorted χ-Fe5C2 phase are formed at 25 bar CO (340 °C) from a Fe oxide precursor. Fe carbide formation was unaffected by Na−S addition, but it did increase Fe oxidation (≤290 °C) and preferred formation of χ-Fe5C2 over θ-Fe3C phase (≥390 °C). The results unify the often ambiguous Fe carbide identification and nomenclature and specify the role of Na−S in the carburization process.

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KW - Iron Carbides

KW - Mössbauer Absorption Spectroscopy

KW - Na−S Promotion

KW - Rietveld Quantitative Phase Analysis

KW - X-ray Powder Diffractometry

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