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Theoretical Microcosmic Dynamics Study of Atom or Molecule on the Transition Metal Surfaces

Author: JiaXiangFeng
Tutor: WangZeXin
School: Shandong Normal University
Course: Physical and chemical
Keywords: gas-surface interaction adsorption potential energy function step defective surface characteristics of critical points.
CLC: O641.1
Type: Master's thesis
Year: 2004
Downloads: 60
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Abstract


The most traditional surface reactions in heterogeneous catalysis plays an important role. Obtaining knowledge of the microscopic details of reactions on high surface area catalysts will be an extremely challenging and interesting task. In particular, the dynamics of interaction of the atoms (such as N, 0, C) and small molecules ( take 02, CO, NO for example) with the transition metal surfaces is awaking more and more interest in the community of chemists and physicists.In this paper, we investigate the 0d, 02 Pd and Nd interaction systems entirely by constructing atom-surface interaction potential, named five parameters Morse potential (5-MP for short). It has practical significant that the research about the interaction of the atoms and molecules on the stepped surface systems.The mainly contents of this paper:Above all, the elementary theory for calculation in this paper and the surface cluster model are given. The present situation of research, the experimental and theoretical methods in common use are simple introduced, and the self-practical method and cluster modes used in this paper are represented in detail.Secondly, we study the adsorption and diffusion of oxygen atom on Pd surfaces.Thirdly, we make a dynamic study of adsorption and disorption of the oxygen molecules on Pd surfaces and probe into the adsorption and diffusion of NO molecules .on the Pd surfaces.The mainly production of this paper:The first, the five parameters Morse potential (5-MP for short) are broughtforward in the study of 0-Pd system. We make an entirely study in particular about"Oxygen Atom Adsorption and Diffusion on Pd low-index Surfaces and (311) steppedSurface" . We find that the oxygen atom adsorb in hep and fee sites on Pd (111) surfacewith the similar critical characteristics, such as vibrational frequencies, bindingenergies, which is difficult to distinct in experiments. Therefore, we take for the fee and hep hollow sites as the identified sites. It is well known that 0 preferentially adsorbs at the highest-coordinated site available on the surface. For example, It adsorbs at the fourfold sites of fee(100) surfaces and at the threefold sites of fee(111) surface. These surfaces contain only one kind of high-coordinated site, whereas some open surfaces offer both threefold and fourfold sites. The question arises then at which site the adsorption occurs. In experiment, the formation of a (2X4)pg structure was observed, and the existence of zig-zag chains on Pd (311) would require the occupation of three- as well as four-fold sites. But they could not conclude whether the 0 atoms occupied three-fold or four-fold hollows when forming the (2X4)pg phase on Pd(311). We find oxygen atoms can adsorb stably in four-fold hollow sites (H4) and three-fold sites (Hh) on the Pd(311) surface. The state that oxygen located in three-fold sites (H,-) is the metastable adsorption, at low coverage oxygen atom favors the four-fold site (H,,). The paper has been publiced in Vol.22 of Chinese Journal of Chemistry.The second, basing on the study of 0-Pd system, we study the interaction of 0^ molecules with Pd flat surfaces using the extend LEPS constructed by 5-MP potential. We find it is more difficult to dissociate that 0. molecules on the density Pd(lll) than on the Pd(lOO) and (110) surfaces. About the queer dynamics phenomenon, we put forward two new concepts: the molecular dissociation limit and the surface dissociation distance. Which illuminate the dissociation mechanism of the 02 on the low-index surfaces and offer the answer to the question "Why does 02 dissociate more .difficulty on the (111) surface than on the (100) and (110) surfaces?" The two new concepts bring interesting for the experts in this majority and are appraised well by them. This paper has been accept and to publish by Journal of Physics Chemistry (see in page 49).The third, and the interaction of NO molecules with Pd flat and stepped surfaces (for example, (311) and (511) stepped surfaces has been discuss in this paper.The studies of interactions

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