Carbon Chain Growth Mechanism of Higher Alcohols Formation from Syngas on CuFe (100) and (110)
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摘要: CuFe混合催化剂是一种重要的合成气制低碳醇用催化剂。为深入了解合成气制低碳醇的反应机理,从量子尺度利用密度泛函理论(DFT)研究了CuFe混合催化剂两个主要表面(100)及(110)上的碳链增长机理。计算发现Cu在Fe (100)及Fe (110)面上倾向于单层聚集分布,CuFe (100)面上CO活化机理为H辅助CO生成CHO,随后逐步加氢生成CH2O和CH3O,CH3O更倾向于生成CH3OH,其碳链增长方式为CHO插入;CuFe (110)面上CO活化机理与(100)面上相同,H辅助CO加氢生成CHO,并不断加氢依次生成CH2O和CH3O,但CH3O更倾向于生成CH3,CH3进一步与CO耦合完成碳链的增长。Abstract: CuFe catalyst is an important catalyst for higher alcohols formation from syngas. In order to gain mechanistic insight into the reaction, spin-polarized density functional theory calculations were performed to investigate the growth mechanism of carbon chains on CuFe (100) and (110) surfaces. The calculated results show that Cu atoms prefer to aggregate rather than homogeneously disperse on the Fe (100) and (110) surfaces. With the increase of Cu atoms, the surface energy decreases gradually, suggesting that the surface tends to be more stable. The dominant activation mechanism of CO on CuFe (100) surfaces is ascribed to a H-assisted CO dissociation via CHO intermediate, which is then progressively hydrogenated to form CH2O and CH3O. Subsequently, CH3O is dominantly hydrogenated to form CH3OH. The pathway of carbon chain growth is found to be CHO rather than CO insertion. The activation mechanism of CO on CuFe (110) surface is found to be similar to that on CuFe (100) surface. The pathway of CH3O formation is CO+3H→CHO+2H→CH2O+H→CH3O. On the CuFe (110) surface, CH3 formation is more thermodynamically favorable than CH3OH, which leads to the production of more CH3 for CO insertion to form C2+ higher alcohols. This research offers mechanistic insight into improving the production of higher alcohols on CuFe catalyst.
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Key words:
- CuFe /
- syngas /
- higher alcohol /
- carbon chain growth /
- DFT
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表 1 Cu原子排布方式不同时Fe (100)和Fe (110)表面的表面能
Table 1. Surface energy on Fe (100) and Fe (110) surfaces with different Cu atom distribution methods
Fe (100) Esurf/(J·m−2) Fe (110) Esurf/(J·m−2) Cu0 6.32 Cu0 7.60 Cu4 5.91 Cu3 7.14 Cu4(2) 5.98 Cu3(2) 7.39 Cu8 5.61 Cu6 6.76 Cu8(2) 5.66 Cu6(2) 6.95 Cu12 5.18 Cu9 6.36 Cu12(2) 5.32 Cu9(2) 6.41 Cu16 4.98 Cu12 5.94 表 2 CuFe (100)及CuFe (110)面上所有物种的最稳定吸附位及吸附能
Table 2. Most stable adsorption sites and adsorption energies of species on CuFe (100) and CuFe (110) surfaces
Species CuFe (100) CuFe (110) Adsorption site Eads/eV Bonding atom Adsorption site Eads/eV Bonding atom C Hollow −7.50 C LB −9.07 C O Hollow −6.10 O LB −6.23 O H Hollow −2.88 H TF −5.28 H CO Hollow −1.61 C TF −2.52 C CHO Bridge-Hollow-Bridge −2.28 C,O TF-LB-TF −3.93 C,O CH2O Hollow −3.61 C,O SB-TF-SB −4.67 C,O CH3O Hollow −2.37 O LB −4.37 O COH Hollow −3.82 C LB −5.09 C CHOH Bridge −3.10 C LB-TF −4.06 C CH2OH Top-Bridge-Top −2.41 C,O T-SB-T −2.72 C,O CH3OH Top-Hollow −1.24 O T-TF −2.66 C CH Hollow −6.58 C LB −6.78 C CH2 Hollow −4.50 C LB −5.23 C CH3 Bridge −2.20 C TF −3.72 C CH4 Top −0.38 ― T ― ― C2H6 Bridge-Top-Bridge −0.13 ― TF-T-TF ― ― CH3CO Top-Bridge-Top −3.85 C,O T-SB −3.48 C,O CH3CHO Top-Bridge −3.58 O T-SB −4.16 O -
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