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. (February 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: 2015-02
• Subjects: Iron carbides -- Carburization -- Morphology -- Fischer–Tropsch synthesis -- DFT; Catalysts -- Periodicals; Catalysis -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; 660.2995
• DOI: 10.1179/2055075814Y.0000000007
• Languages: English
• ISSNs: 2055-074X

Abstract

Abstract : 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-Fe2 C, χ-Fe5 C2, θ-Fe3 C and Fe4 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 H2 /CO ratio can suppress carburization ability. Under wide ranging gas environment, ε-Fe2 C, χ-Fe5 C2 and θ-Fe3 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 ΔμC . 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-Fe5 C2 -(100)-2.25 is most favored for CO adsorption and CH4 formation, followed by θ-Fe3 C-(010)-2.33, ε-Fe2 C-(12 1)-2.00 and Fe4 C-(100)-3.00, in line with surface work function and the charge of the surface carbon atoms.