First-principles study on the CO adsorption and electronic properties of Fe (111) modified by Cu single atom
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摘要: 采用密度泛函理论方法研究了Cu单原子修饰对Fe（111）表面CO吸附性能和电子性质的调变作用，其中，Cu单原子修饰研究了吸附和取代两种方式。结果表明，CO在Cu修饰的Fe（111）面吸附能力都会变弱，一是Cu原子自身提供的位点对CO的吸附较弱；二是Cu会使其附近的Fe对CO的吸附变弱。分析电子性质表明，Cu作用于Fe表面后，会导致Cu附近Fe原子部分电子向Cu原子转移，进而削弱了Fe与吸附分子间电子交互作用而改变Fe原子的吸附能力。故Cu原子改性Fe表面可以很好地调变CO的吸附、解离及后续反应催化活性，这为进一步探究Cu改性Fe表面的合成气催化反应机理提供了基础信息。Abstract: In this paper, the effect of Cu single atom modification on the adsorption of CO and electronic properties of Fe (111) surface has been studied by density functional theory (DFT). Two ways of adsorption and substitution have been studied for Cu mono-atom modification. The results show that the adsorption capacity of CO on the Cu modified Fe (111) becomes weak. One reason is that the sites provided by the Cu atom itself are weak for CO, and the other is that Cu weakens the adsorption of CO on the Fe nearby Cu. The analysis of electronic properties indicates that when Cu acts on the Fe (111), the part electrons of Fe can be transferred to the Cu, which weakens the electronic interaction between Fe and adsorbed molecules, and adjusts its adsorption capacity. Therefore, the Fe surface modified by Cu atom can well adjust the adsorption, dissociation and subsequent reaction catalytic activity of CO, which provides basic information to further explore the syngas catalytic reaction mechanism of Cu modified Fe surface.
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Key words:
- Fe (111) /
- density functional theory /
- monoatomic Cu modification /
- CO adsorption
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图 1 Cu在Fe (111)面的稳定作用结构和对应能量
Figure 1 Stability of structure and the corresponding energy of Cu acted with Fe(111)
(a): Cu adsorbed on deep hole; (b): Cu adsorbed on the shallow hole; (c): Cu instead of surface Fe; (d): Cu instead of subsurface Fe (light blue for the outermost Fe, gray for subsurface Fe, dark blue for the third layer of Fe)
图 2 CO在Cu吸附的Fe(111)面的稳定结构和对应吸附能
Figure 2 Optimized structures and the corresponding adsorption energies of CO adsorbed on different sites of Cu-ads-DH
图 3 CO在Cu替换一个Fe原子的稳定结构和对应吸附能
Figure 3 Optimized structures and the corresponding adsorption energies of CO adsorbed on different sites of Cu-sub-OM
图 4 三种表面的态密度分布
Figure 4 Density of states for three surface models
(a): pure Fe(111); (b): Cu-ads-DH; (c): Cu-sub-OM (1stFe refer to the outermost layer Fe, 2ndFe refer to the sublayer Fe, Cu refer to adsorbed or substituted Cu)
图 5 Cu改性模型的差分电荷示意图
Figure 5 Difference charge density of Cu-ads-DH and Cu-subs-OM
(a): Cu-ads-DH; (b): Cu-subs-OM (left for 3D distribution, right for 2D section distribution)
图 6 CO在纯Fe (111)、Cu-ads-DH和Cu-subs-OM表面1stFe顶位吸附的Fe-C和C-O键-COHP和对应原子PDOS
Figure 6 -COHP of C-O bond and PDOS of Fe (C) for three models
(a)-(d): CO adsorbed on pure Fe (111); (e)-(f): CO adsorbed on Cu-ads-DH; (i)-(l): CO adsorbed on Cu-subs-OM
表 1 CO在纯Fe (111)、Cu-ads-DH和Cu-sub-OM三种不同表面吸附能及C-O键长比较
Table 1 Comparison of adsorption energy (eV) and bond length (nm) of CO on pure Fe (111) surface and Cu modified Fe (111)
Adsorption site Fe (111) Cu-ads-DH Cu-subs-OM dM-C dC-O Eads dM-C dC-O Eads dM-C dC-O Eads CO top-Cu - - - 0.1517 - -1.10 0.1526 - -1.10 top-1thFe 0.1586 - -1.95 0.1705 - -1.55 0.1584 - -1.36 (adjacent Cu) 0.1672 top-2thFe 0.1603 - -2.68 0.1760 - -1.84 0.1672 - -1.94 (adjacent Cu) 0.1806 0.1763 Fe-Fe-bri -2.52 -1.91 -2.09 
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表 2 纯Fe (111)、Cu-ads-DH和Cu-subs-OM三种结构表层原子Bader电荷分析
Table 2 Bader charge of surface atoms of pure Fe (111) and Cu-ads-DH and Cu-subs-OM models
Fe(111) Cu-ads-DH Cu-subs-OM Cu-Δ(e) - 0.239 0.147 1stFe-Δ(e) -0.086 -0.101 -0.032 2ndFe-Δ(e) 0.160 0.032 0.035 (1stFe+ 2ndFe) -Δ(e) 0.074 -0.069 0.003
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