CO Activation Pathways of Fischer鈥揟ropsch Synthesis on 蠂-Fe5C2 (510): Direct versus Hydrogen-Assisted CO Dissociation

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• 作者：Thanh Hai Pham ; Xuezhi Duan ; Gang Qian ; Xinggui Zhou ; De Chen
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：May 15, 2014
• 年：2014
• 卷：118
• 期：19
• 页码：10170-10176
• 全文大小：383K
• 年卷期：v.118,no.19(May 15, 2014)
• ISSN：1932-7455

文摘

Iron carbides, especially 蠂-Fe₅C₂, among the active iron species in Fischer鈥揟ropsch synthesis (FTS), are considered to be responsible for high FTS activity. CO activation pathways as the initial steps of FTS over 蠂-Fe₅C₂ were explored by spin-polarized density functional theory calculations. Surface energies of 蠂-Fe₅C₂ facets observed from the XRD patterns were first calculated, and then the corresponding equilibrium 蠂-Fe₅C₂ shape was obtained by Wulff construction. The thermodynamically stable (510) surface was predicted to have the largest percentage among the exposed crystal facets. Subsequently, the adsorption properties of CO on 蠂-Fe₅C₂ (510) were studied. Despite exhibiting lower binding energy than that at the 3F-4 site as the most stable configuration, CO adsorption at the 4F-1 site led to significant weakening of the C鈥揙 bond from both the structural and electronic properties鈥?points of view. Furthermore, two kinds of CO activation mechanisms (i.e., the direct and H-assisted CO dissociation) and the corresponding six kinds of CO activation pathways on 蠂-Fe₅C₂ (510) were comparatively investigated on the basis of the evolution of carbon species, in which the C鈥揙 bond cleavage and further hydrogenation of surface species were concerned. The systematic analysis of the activation properties of CO suggests the direct CO dissociation as the preferred activation pathway.