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Rietveld and pair distribution function study of Hägg carbide using synchrotron X-ray diffraction

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dc.contributor.author Kruger, G.J.
dc.contributor.author Steuwer, A.
dc.contributor.author Brunelli, M.
dc.contributor.author Du Plessis, Hester Esna
dc.contributor.author De Villiers, J.P.R.
dc.date.accessioned 2012-10-17T08:55:15Z
dc.date.available 2012-10-17T08:55:15Z
dc.date.issued 2011
dc.identifier.citation Du Plessis, H.E., De Villiers, J.P.R., Kruger, G.J., Steuwer, A. & Brunelli, M. 2011. Rietveld and pair distribution function study of Hägg carbide using synchrotron X-ray diffraction. Journal of Synchrotron Radiation, 18(2):266-271. [http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1600-5775] en_US
dc.identifier.issn 0909-0495
dc.identifier.uri http://hdl.handle.net/10210/7871
dc.description.abstract Fischer-Tropsch (FT) synthesis is an important process in the manufacturing of hydrocarbons and oxygenated hydrocarbons from mixtures of carbon monoxide and hydrogen (syngas). The reduced iron catalyst reacts with carbon monoxide and hydrogen to form bulk Fe(5)C(2) Hägg carbide (χ-HC) during FT synthesis. Arguably, χ-HC is the predominant catalyst phase present in the working iron catalyst. Deactivation of the working catalyst can be due to oxidation of χ-HC to iron oxide, a step-wise decarburization to cementite (θ-Fe(3)C), carbon formation or sintering with accompanying loss of catalytic performance. It is therefore critical to determine the precise crystal structure of χ-HC for the understanding of the synthesis process and for comparison with the first-principles ab initio modelling. Here the results of high-resolution synchrotron X-ray powder diffraction data are reported. The atomic arrangement of χ-HC was confirmed by Rietveld refinement and subsequent real-space modelling of the pair distribution function (PDF) obtained from direct Fourier transformation. The Rietveld and PDF results of χ-HC correspond well with that of a pseudo-monoclinic phase of space group Pī [a = 11.5661 (6) Å, b = 4.5709 (1) Å, c = 5.0611 (2) Å, α = 89.990 (5)°, β = 97.753 (4)°, γ = 90.195 (4)°], where the Fe atoms are located in three distorted prismatic trigonal and one octahedral arrangement around the central C atoms. The Fe atoms are distorted from the prismatic trigonal arrangement in the monoclinic structure by the change in C atom location in the structure. en_US
dc.language.iso en en_US
dc.publisher National Center for Biotechnology Information, J Synchrotron Radiat. 2011 en_US
dc.rights International Union of Crystallography, 2011. The final publication is available at: http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1600-5775 en_US
dc.subject Fischer-Tropsch synthesis en_US
dc.subject Hägg carbide en_US
dc.subject Hydrocarbons en_US
dc.subject Rietveld refinement en_US
dc.subject Real-space modelling en_US
dc.subject Pair distribution function en_US
dc.subject Fourier transformation en_US
dc.title Rietveld and pair distribution function study of Hägg carbide using synchrotron X-ray diffraction en_US
dc.type Article en_US

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