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Mechanism for Atom、Molecular Adsorption on Simple Metal and Transition Metal Surface

Author: WuHongZhang
Tutor: DiaoZhaoYu
School: Shandong Normal University
Course: Physical and chemical
Keywords: atom molecule adsorption diffusion 5-MP LEPS potential
CLC: O647.31
Type: Master's thesis
Year: 2009
Downloads: 57
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Abstract


The dynamics of gas-solid surface interaction is arousing more and more interest in the community of physicists and chemists. Whether multi-phase catalysis or colloid catalyzed interaction is relating to the interaction between reactants as well as between reactant and catalyzer surface. Therefore, the systemic study on the interaction between atom, molecule and catalyzer surface, especially the interaction with active sites in theory is necessary. Some representative atoms and molecules are selected to study the kinetic behavior of adsorption and diffusion on the flat and defective surfaces by employing five-parameter Morse potential and improved extended LEPS potential in this dissertation. The main content in this paper is as follows:Chapter 1: the significance, status in quo and methods of the investigation in gas-solid surfaces interaction are expatiated. On the other hand the theory methods and cluster modes used in this work are introduced in detail.Chapter 2: O-Al system, H-Ir system and H-Al system are studied using 5-parameter Morse potential (5-MP) method.Chapter 3: The characteristics of adsorption site and state for CO molecule on Pt(335),(112) surfaces and CO molecule on Pt(997),(553) surfaces are investigated by extended LEPS method.The main production of this paper:1. O-Al system. The caculated results show that O atoms are located at the there-fold hollow site and the octahedral site of the Al(111) with the perpendicular vibrational mode 621 (619) cm-1 and 880 (887) cm-1, the parallel vibrational mode 880 (887) cm-1 and 437 cm-1. For Al(100) system, O atoms are located at the four-fold hollow site and the tetrahedral site. With respect to Al(110) system, the preferential adsorption states are the quasi-3-fold site and the octahedral site and not the long bridge site.2. H-Ir system. The H-Ir surface adsorption system is studied using 5-MP method, and its critical characteristics, such as adsorption site, adsorption geometry, binding energy and eigenvalue for vibration, were obtained. The calculated results demonstrate that H adsorbs at high symmetry site on Ir surfaces. The adatom H adsorbs at three-fold hollow site on (111) surface with the perpendicular vibrational mode 559 cm-1; H adsorbs at three-fold hollow site on (110) surface with the perpendicular vibrational mode 617 cm-1. The calculated results conform to the experimental results, and forecast some new characters.3. H-Al system. The calculated results demonstrate that H adsorbs at high symmetry site on Ir surfaces. The adatom H adsorbs at the top and bridge sites on (100) surface with the perpendicular vibrational modes 1870 and 1273 cm-1; H adsorbs at top and short bridge sites on (110) surface with the perpendicular vibrational modes 1868 and 1376 cm-1. H adsorbs at top and bridge sites on (111) surface with the perpendicular vibrational modes 1871 and 1281 cm-1. The calculated results conform to the experimental results.4. CO-Pt(335)、(112) system. The calculated results show that there exist common characteristics of CO adsorption on the two surfaces. On both Pt (335) and (112) stepped surfaces, CO molecules adsorb on the step top site initially. With the coverage increasing, CO molecules diffuse from the step top sites to the stable terrace bridge sites, and the terrace top sites sequentially. However, the step bridge site only corresponds to a transition state on the two surfaces. The predicions for vibrational frequency are in good agreement with the experimental results.5. CO-Pt(997)、(553) system. The calculated results indicate that there exist common characteristics of CO adsorption on the two surfaces. At low coverage, CO molecules adsorb on the step top site and terrace top site; with the coverage increasing, CO molecules begin to occupy the terrace bridge site. The calculatons for vibrational frequency are in good agreement with the experimental results.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > The physical chemistry of surface phenomena > Adsorption > Adsorption theory
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