Quantum-Chemical DFT Study of Direct and H- and C-Assisted CO Dissociation on the χ-Fe5 C2 Hägg Carbide

The Journal of Physical Chemistry. C, Nanomaterials and Interfaces
Robin J P BroosEmiel J M Hensen

Abstract

The first step in the Fischer-Tropsch reaction is the production of C1 monomers by the dissociation of the C-O bond. Although Fe is the active metal, it is well known that under typical reaction conditions, it changes into various carbide phases. The Hägg carbide (χ-Fe5C2) phase is usually considered as the catalytically active phase. We carried out a comprehensive DFT study of CO dissociation on various surface terminations of the Hägg carbide, selected on their specific site topology and the presence of stepped sites. Based on the reaction energetics, we identified several feasible CO dissociation pathways over the Hägg carbide. In this study, we have compared the direct CO dissociation with H- and C-assisted CO dissociation mechanisms. We demonstrated that the reaction rate for CO dissociation critically depends on the presence and topology of interstitial C atoms close to the active site. Typically, the CO dissociation proceeds via a direct C-O bond scission mechanism on the stepped sites on the Fe carbide surface. We have shown a preference for the direct CO dissociation on the surfaces with a stepped character. The H-assisted CO dissociation, via a CHO intermediate, was preferred when the surface did not have a clear step...Continue Reading

References

Aug 15, 1989·Physical Review. B, Condensed Matter·M Methfessel, A T Paxton
Sep 29, 2009·Journal of the American Chemical Society·Chun-Fang HuoHaijun Jiao
Oct 12, 2010·Journal of the American Chemical Society·Emiel de SmitBert M Weckhuysen
Feb 13, 2008·Journal of Physics. Condensed Matter : an Institute of Physics Journal·P J SteynbergW Janse van Rensburg
Mar 16, 2012·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Ashriti GovenderJ W Hans Niemantsverdriet
Oct 24, 2013·Journal of the American Chemical Society·Jin-Xun LiuWei-Xue Li

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Vienna ab initio simulation package

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