Density functional study of water gas shift reaction catalyzed by Cu-Pt-Au ternary alloy
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摘要: 利用密度泛函理论（DFT）研究了不同掺杂量的Cu-Pt-Au催化剂性质及水煤气变换反应（WGSR）在催化剂表面上的反应机理。首先对Cu-Au和Pt-Au二元催化剂的稳定性和电子活性进行研究，发现Pt-Au催化剂的协同效应较优，稳定性更优，结合能为77.15 eV，d带中心为-3.18 eV。当将Cu继续掺杂到Pt-Au合金中构成Cu-Pt-Au三元催化剂时，Cu3-Pt3-Au（111）结合能为77.99 eV，且d带中心为-3.05 eV，表明其具有较优的稳定性和电子活性。探讨了WGSR在Cu3-Pt3-Au（111）上的反应历程，氧化还原机理因CO氧化的能垒达到4.84 eV而不易进行。CHO和COOH两个中间体为竞争关系，且形成CHO中间物时的能垒较小，因此，反应相对容易按照甲酸机理进行。
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关键词:
- 密度泛函理论 /
- 水煤气变换反应(WGSR) /
- 机理 /
- 三元合金
Abstract: The reaction path and the reaction mechanism of water gas shift reaction (WGSR) on the Cu-Pt-Au catalyst surface were investigated using density functional theory (DFT). The stability and electron activity of binary and ternary catalysts composed of Cu, Pt and Au were studied. The synergistic effect of Pt-Au catalyst in binary alloy is better, and the binding energy of Pt3-Au(111) surface is 77.15 eV, and energy level of d-band center is -3.18 eV. When the Pt3-Au(111) surface continues to be doped with Cu, the binding energy of Cu3-Pt3-Au(111) is 77. 99 eV and the center of d-band is -3. 05 eV according to the binding energy and density of stares. The energy barrier of CO oxidization is 4.84 eV in the redox mechanism. The reaction is not easy to follow the redox mechanism. Moreover, the two intermediates CHO and COOH are competitive, the energy barrier of forming COOH is larger than that of forming CHO, the reaction is more easily carried out according to the formic acid mechanism.-
Key words:
- density functional theory /
- water gas shift reaction(WGSR) /
- mechanism /
- ternary alloy
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图 5 各机理在Cu3-Pt3-Au(111)上的能量变化
Figure 5 Diagram for relative energy of reaction mechanisms on Cu3-Pt3-Au(111)
表 1 不同掺杂比例催化剂的结合能
Table 1 Binding energy of metal surfaces with different doping amounts
Surface ΔEb/eV Surface ΔEb/eV Surface ΔEb/eV Surface ΔEb/eV Surface ΔEb/eV Cu1-Au 72.35 Pt3-Au 77.15 Cu1-Pt1-Au 74.05 Cu1-Pt2-Au 75.76 Cu1-Pt3-Au 77.52 Cu2-Au 72.70 Pt1-Au 73.61 Cu2-Pt1-Au 74.38 Cu2-Pt2-Au 76.07 Cu2-Pt3-Au 77.79 Cu3-Au 72.97 Pt2-Au 75.36 Cu3-Pt1-Au 74.62 Cu3-Pt2-Au 76.29 Cu3-Pt3-Au 77.99 
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表 2 不同掺杂比例Au(111)的d带中心
Table 2 d-band center of different doping ratio Au(111)
Surface Surface Surface Surface Surface Cu1-Au -3.34 Pt1-Au -3.32 Cu1-Pt1-Au -3.26 Cu1-Pt2-Au -3.20 Cu1-Pt3-Au -3.14 Cu2-Au -3.29 Pt2-Au -3.25 Cu2-Pt1-Au -3.22 Cu2-Pt2-Au -3.15 Cu2-Pt3-Au -3.09 Cu3-Au -3.24 Pt3-Au -3.18 Cu3-Pt1-Au -3.17 Cu3-Pt2-Au -3.11 Cu3-Pt3-Au -3.05
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表 3 不同掺杂比例金属表面上的CO和H2O的吸附能及结构参数
Table 3 Adsorption energy and structural parameters of CO and H2O on metal surfaces with different doping ratios
Surface-CO Site C-O
(nm)Eads
/eVSurface-H2O Site O-H1
(nm)O-H2
(nm)Bond angle Eads
/eVCu1-Au(111) Top-Cu 0.1150 -0.86 Cu1-Au(111) Top-Cu 0.0979 0.0979 104.144 -0.50 Cu2-Au(111) Bri-Cu 0.1174 -0.88 Cu2-Au(111) Top-Cu 0.0976 0.0978 104.462 -0.54 Cu3-Au(111) Bri-Cu 0.1171 -0.92 Cu3-Au(111) Bri-Cu 0.0995 0.1055 104.444 -0.55 Pt1- Au(111) Top-Pt 0.1156 -1.92 Pt1- Au(111) Top-Pt 0.0977 0.0977 104.552 -0.46 Pt2- Au(111) Bri-Pt 0.1185 -2.02 Pt2- Au(111) Top-Pt 0.0977 0.0976 104.446 -0.4 Pt3- Au(111) Bri-Pt 0.1184 -2.08 Pt3- Au(111) Bri-Pt 0.0971 0.0971 104.674 -0.18 Cu1-Pt1-Au(111) Top-Pt 0.1157 -1.97 Cu1-Pt1-Au(111) Top-Cu 0.0978 0.0977 104.570 -0.50 Cu1-Pt2-Au(111) Top-Pt 0.1157 -2.00 Cu1-Pt2-Au(111) Top-Cu 0.0976 0.0977 104.658 -0.53 Cu1-Pt3-Au(111) Top-Pt 0.1156 -1.86 Cu1-Pt3-Au(111) Top-Cu 0.0977 0.0982 103.876 -0.55 Cu2-Pt1-Au(111) Top-Pt 0.1157 -2.00 Cu2-Pt1-Au(111) Top-Cu 0.0978 0.0981 104.344 -0.49 Cu2-Pt2-Au(111) Top-Pt 0.1157 -2.00 Cu2-Pt2-Au(111) Top-Cu 0.0977 0.0983 104.054 -0.54 Cu2-Pt3-Au(111) Top-Pt 0.1158 -1.95 Cu2-Pt3-Au(111) Top-Cu 0.0978 0.0981 104.046 -0.50 Cu3-Pt1-Au(111) Fcc 0.1141 -2.01 Cu3-Pt1-Au(111) Cu-Pt-Bri 0.0958 0.1018 104.204 -0.54 Cu3-Pt2-Au(111) Top-Pt 0.1159 -2.02 Cu3-Pt2-Au(111) Top-Pt 0.0977 0.0985 102.304 -0.55 Cu3-Pt3-Au(111) Fcc 1.188 -2.32 Cu3-Pt3-Au(111) Cu-Pt-Bri 0.979 0.974 104.138 -0.54
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表 4 Mulliken电荷布局分析
Table 4 Mulliken charge population analysis
Atom Free charge(e) Adsorption charge(e) CCO 0.096 0.611 OCO -0.096 -0.178 HH2O 0.245 0.266 HH2O 0.245 0.269 OH2O -0.490 -0.412 Total 0 0.556
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表 5 Cu3-Pt3-Au(111)表面上小分子的吸附能
Table 5 Adsorption energy of different small molecules on the Cu3-Pt3-Au(111) surface
Molecule Eads/eV Top-Cu Top-Pt Bri-Cu Bri-Pt Cu-Pt-Bri Hcp Fcc CO -2.12 -1.94 -1.94 -2.40 -2.32 -2.18 -2.32 CO2 -0.09 -0.11 -0.09 -0.02 -0.12 -0.11 -0.10 O -4.38 -4.39 -4.54 -4.38 -4.54 -4.29 -4.54 H -2.79 -2.49 -2.39 -3.03 -3.03 -2.88 -2.89 H2O -0.37 -0.39 -0.27 -0.39 -0.54 -0.66 -0.26 COOH -1.78 -2.68 -1.79 -2.71 -2.77 -1.54 -1.68 OH -2.50 -2.97 -2.98 -2.71 -2.98 -2.75 -2.99 H2 -0.06 -0.07 -0.05 -0.07 -0.06 -0.11 -0.08 HCOO -2.61 -2.66 -2.50 -2.66 -2.66 -2.45 -2.65 CHO -1.47 -2.63 -1.47 -2.63 -2.61 -2.75 -2.69
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表 6 Cu3-Pt3-Au(111)表面上各基元反应的活化能(Ea)、反应热(ΔE)和速率常数k
Table 6 Energy barriers, reaction heat and k of primer reactions on Cu3-Pt3-Au(111)
Mechanism Element reaction Cu3-Pt3-Au(111) Ea/eV ΔE/eV k/(cm3·mol-1·s-1) 1: H2O+*=H*+OH* 0.02 0.01 4.85×1014 Redox mechanism 2-a: OH*=O*+H* 1.24 0.49 6.35×1013 2-b: OH*+OH*=H2O*+O* 1.36 1.35 5.33×1012 3: CO*+O*=CO2*+* 4.84 -0.05 8.30×1012 Carboxyl mechanism 4: CO*+OH*=COOH*+* 3.15 0.48 1.99×1011 5-a: COOH*+*=H*+CO2* 0.19 -0.19 2.29×1012 5-b: COOH*+OH*=H2O*+CO2* 1.07 -0.20 1.67×1012 Formate mechanism 2-a: OH*=O*+H* 1.24 0.49 6.35×1013 6: CO*+H*=CHO* 0.51 0.05 2.85×1012 7: CHO*+O*=HCOO* 0.85 -0.02 4.14×1013 8: HCOO*+*=CO2*+H* 3.09 -0.24 7.03×1012 9: 2H*=H2*+2* 0.43 -0.08 6.70×1013
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