Rh-Decorated Cu Alloy Catalyst for Improved C2 Oxygenate Formation from Syngas

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• 作者：Yong-Hui Zhao ; Ming-Mei Yang ; Dapeng Sun ; Hai-Yan Su ; Keju Sun ; Xiufang Ma ; Xinhe Bao ; Wei-Xue Li
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：September 22, 2011
• 年：2011
• 卷：115
• 期：37
• 页码：18247-18256
• 全文大小：1112K
• 年卷期：v.115,no.37(September 22, 2011)
• ISSN：1932-7455

文摘

C₂ oxygenate (acetaldehyde, ethanol, etc.) formation from syngas (CO + H₂) is an important industrial process for the production of clean liquid energy fuels and valuable chemical feedstocks that are catalyzed industrially by Rh modified with Mn and Fe, etc. In an effort to identify catalysts based on less expensive metals and higher C₂ oxygenate selectivity, density functional theory (DFT) calculations were performed to tune the relative activity of the selectivity-determining steps, i.e., CO insertion in CH_x (x = 1, 2, 3) versus CH_x hydrogenation by changing composition and structure of material. We find that the Rh-decorated Cu alloy catalyst has significantly lower CO insertion barriers compared to pristine Rh(111) and vicinal Rh(553) surfaces, whereas the variation of CH_x hydrogenation barriers on the three surfaces is modest. A semiquantitative kinetic analysis based on DFT calculations shows that the C₂ oxygenate selectivity on RhCu(111) is substantially improved, with the production rate of C₂ oxygenates slightly higher than CH₄ under experimental conditions, compared with Rh(111) and Rh(553) that are highly selective to CH₄. Our calculations suggest that the improved C₂ oxygenate selectivity on the RhCu alloy is primarily due to the fact that CO insertion is rather sensitive, whereas hydrogenation is insensitive to the ensemble effect. Furthermore, the Rh-decorated Cu alloy has stronger resistance toward coking and lower constituent cost compared to pure Rh catalysts and is thus a promising candidate for an improved C₂ oxygenate synthesis catalyst.