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Theoretical Investigation of Carbon Monoxide Adsorption on the Nickel Surface in the Macroscopic and Microscopic Scales

Shamkhali, Amir Nasser | 2010

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 40546 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Parsafar, Gholamabbas
  7. Abstract:
  8. In this work, CO interaction with macroscopic Ni(111) surface and microscopic Nin (n = 2-4) clusters were investigated. First, the CO interaction with various adsorption sites were studied by DFT methods on Ni(111) surface. On the basis of these calculations, hcp site has the strongest interaction with CO adsorbate. Then, the vibrational frequencies of C=O and adsorptive bond on the hcp site were calculated and the results show that anharmonicity of adsorptive bond is more important than C=O bond. Therefore, three potential models are considered for adsorptive bond and the effect of potential models on its thermodynamic properties was investigated. The results show that the effect of anharmonicity on the heat capacity and entropy is more than other properties due to the dependency of these properties to the separation of energy levels. Also, cluster models of adsorption sites on the Ni(111) surface were used for partial optimization and the calculation of vibrational frequencies of CO on the surface by DFT methods for four coverage values. Then, the effect of side by side interactions on the vibrational frequencies and thermodynamic properties of adsorbates were studied. The results show that the coupling between CO vibrational modes and surface phonons reduces the side effects and adsorption system acts as an intelligent material in such a way that when the repulsive forces exert more instability to the system at the higher coverage values, the system changes its configuration in order to reduce these repulsive interactions. Also, CO interaction with mentioned Ni clusters was studied by DFT methods and thermodynamic properties for CO interaction with the Ni clusters were calculated .The results show that chemical activity of CO on the Ni clusters is more than that of the macroscopic surface and there are some behavior for thermodynamic properties in the microscopic scale which can not be observed in the macroscopic scale due to the large number of particles
  9. Keywords:
  10. Adsorption ; Thermodynamic Properties ; Lateral Interaction ; Cluster Analysis ; Density Functional Theory (DFT) ; Vibrational Frequency

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