Mechanistic Insight into the C2 Hydrocarbons Formation from Syngas on fcc-Co(111) Surface: A DFT Study

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• 作者：Congbiao Chen ; Qiang Wang ; Guiru Wang ; Bo Hou ; Litao Jia ; Debao Li
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：May 5, 2016
• 年：2016
• 卷：120
• 期：17
• 页码：9132-9147
• 全文大小：1510K
• 年卷期：0
• ISSN：1932-7455

文摘

A comprehensive density functional theory (DFT) calculation of C₂ hydrocarbons formation in Fischer–Tropsch synthesis (FTS) on the close-packed fcc-Co(111) surface has been carried out. The activation barriers and reaction energies for CO dissociation, CH_x hydrogenation, CH_x + CH_y coupling and C(HO) insertion into CH_x, CH_xCH_y–O bond scission, and successive hydrogenation reactions involved in C₂ hydrocarbons formation have been examined, and the following conclusions could be concluded: (i) CH is the dominant monomer, which is formed via CO + H → CHO → CH + O; (ii) CHO insertion is more plausible for C–C chain formation compared with CO insertion and CH_x–CH_y coupling. The rate-determining steps for C₂ hydrocarbons are CO + H → CHO and CHCH + H → CH₂CH. Meanwhile, CH₃ hydrogenation to form CH₄ is more facile than C₂ hydrocarbons, which will lead to the low productivity and selectivity to C₂ hydrocarbons. (iii) Stepped-Co(111) surface has been modeled to clarify the role of defects during C₂ hydrocarbons formation, and the calculation results indicate that CHO and CH₂CH formation could be facilitated and CH₄ formation could be suppressed, suggesting that the step sites could effectively promote the catalytic activity and selectivity for C₂ hydrocarbons formation.