Determining surface structure and stability of ε-Fe2C, χ-Fe5C2, θ-Fe3C and Fe4C phases under carburization environment from combined DFT and atomistic thermodynamic studies. (January 2015)

• Record Type: Journal Article
• Authors: Zhao, Shu; Liu, Xing-Wu; Huo, Chun-Fang; Li, Yong-Wang; Wang, Jianguo; Jiao, Haijun
• Is Part Of: Catalysis, structure & reactivity. Volume 1:Number 1(2015)
• Page Start: 44
• Page End: 60
• Publication Date: 2015-01
• Subjects: Catalysts -- Periodicals; Catalysis -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; 660.2995
• DOI: 10.1179/2055075814Y.0000000007
• Languages: English
• ISSNs: 2055-074X

Abstract

<abstract> <title> <x content-type="archive" xml:space="preserve">Abstract</x> </title> <p>The chemical–physical environment around iron based FTS catalysts under working conditions is used to estimate the influences of carbon containing gases on the surface structures and stability of ε-Fe<sub>2</sub>C, χ-Fe<sub>5</sub>C<sub>2</sub>, θ-Fe<sub>3</sub>C and Fe<sub>4</sub>C from combined density functional theory and atomistic–thermodynamic studies. Higher carbon content gas has higher carburization ability; while higher temperature and lower pressure as well as higher H<sub>2</sub>/CO ratio can suppress carburization ability. Under wide ranging gas environment, ε-Fe<sub>2</sub>C, χ-Fe<sub>5</sub>C<sub>2</sub> and θ-Fe<sub>3</sub>C have different morphologies, and the most stable non-stoichiometric termination changes from carbon-poor to carbon-rich (varying surface Fe/C ratio) upon the increase in Δμ<sub>C</sub>. The most stable surfaces of these carbides have similar surface bonding pattern, and their surface properties are related to some common phenomena of iron based catalysts. For these facets, χ-Fe<sub>5</sub>C<sub>2</sub>-(100)-2.25 is most favored for CO adsorption and CH<sub>4</sub> formation, followed by θ-Fe<sub>3</sub>C-(010)-2.33, ε-Fe<sub>2</sub>C-(1<overline>2</overline>1)-2.00 and Fe<sub>4</sub>C-(100)-3.00, in line with surface work function and the charge of the surface carbon atoms.</p> <p> <graphic xlink:href="ark:/27927/pgh3xb7w69g" position="anchor" orientation="portrait" xmlns:xlink="http://www.w3.org/1999/xlink" /> </p> </abstract>