Effect of Fe and point deficiency on adsorption behavior of NH3 on coke surface: A density functional theory study
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摘要: 采用密度泛函理论,并使用具有周期性边界条件的石墨烯模型近似模拟焦炭表面,研究了Fe原子修饰及点缺陷对NH3在焦炭表面异相吸附的影响。计算结果表明,NH3分子在点缺陷石墨烯表面的吸附属于物理吸附,结合能为-0.381 eV;NH3分子吸附在Fe修饰的完整石墨烯表面属于化学吸附,吸附能为-1.442 eV;Fe原子修饰及点缺陷单独存在下NH3的吸附能均大于NH3在完整石墨烯表面的吸附(吸附能为-0.190 eV)。此外,Fe原子修饰与点缺陷共存对NH3的吸附具有协同作用,结合能达到-3.538 eV,明显大于两者单独存在下NH3的吸附能之和,综合分析Mulliken布居数与态密度,Fe原子与石墨烯表面、NH3分子之间有更多地电荷转移,可以解释两者共存对NH3吸附协同促进的原因。Abstract: Effect of Fe and point deficiency on adsorption behavior of NH3 on coke surface was studied using density functional theory and graphene model with periodic boundary conditions. The results show that the adsorption of NH3 on surface of point-defective graphene belongs to physical adsorption with binding energy of -0.381 eV. The adsorption of NH3 on surface of Fe-modified-graphene belongs to chemical adsorption with energy of -1.442 eV. The adsorption energy of NH3 in the presence of Fe atom or point defect is greater than that of NH3 on the surface of intact graphene. In addition, coexistence of Fe atom and point defect has a synergistic effect on adsorption of NH3 with binding energy of -3.538 eV, which is much higher than the sum of adsorption energy of NH3 in the presence of the two alone. There is more charge transferring among Fe atom, graphene surface and NH3 molecule, which can explain the synergistic effect of coexistence of Fe and point defect.
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Key words:
- density functional theory /
- char /
- NH3 /
- Fe /
- point-deficiency /
- adsorption
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表 1 石墨烯晶胞晶格常数
Table 1 The lattice constants of graphene cell
a/nm b/nm c/nm d/nm Calculated value 0.2452 0.2452 0.6873 0.1416 Experimental value 0.2460 0.2460 0.6800 0.1420[28] Deviation /% 0.33 0.33 1.07 0.28 表 2 Fe在石墨烯表面的结合能与NH3在不同石墨烯表面的吸附能
Table 2 Binding energy of Fe on surface of graphene and adsorption energy of NH3 on different graphene surfaces
Total/eV NH3/eV Gra/eV Dgra/eV Fe/eV EB/eV EB*/eV Fe+Gra -37060.621 - -33165.088 - -3894.255 -1.279 - Fe+Dgra -36022.865 - - -32120.718 -3894.255 -7.891 - NH3+Gra -34703.083 -1537.8045 -33165.088 - - -0.190 0-(-0.17)[29, 30] NH3+Dgra -33658.904 -1537.8045 - -32120.718 - -0.381 -0.24[31] NH3+Fe+Gra -38599.868 -1537.8045 -33165.088 - -3894.255 -1.442 - NH3+Fe+Dgra -37564.207 -1537.8045 - -32120.718 -3894.255 -3.538 - 表 3 不同吸附体系下的原子间距
Table 3 Interatomic distance in different adsorption systems
Interatomic distance /nm dC-C dFe-N dFe-C dFe-H dN-H dN-C dH-C NH3+Dgra 0.2491 - - - 0.1023 0.3452 0.3080 NH3+Fe+Gra 0.1438 0.2078 0.2165 0.2629 0.1024 - - NH3+Fe+Dgra 0.2637 0.2036 0.1772 0.2592 0.1025 - - 表 4 NH3在不同石墨烯表面吸附的Mulliken布居数
Table 4 Mulliken population of NH3 adsorbed on different graphene surfaces
Mulliken population /e Fe N H C1 C2 C3 C4 C5 C6 NH3+Gra - -0.462 0.151 -0.002 -0.001 -0.002 -0.003 -0.001 -0.002 NH3 - -0.470 0.157 - - - - - - NH3+Dgra - -0.489 0.176 -0.068 -0.064 -0.061 - - - NH3+Fe+Gra 0.136 -0.550 0.153 -0.013 -0.013 -0.016 -0.014 -0.015 -0.014 NH3+Fe+Dgra -0.209 -0.884 0.288 -0.014 -0.018 -0.020 - - - -
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