Theoretical Study Of Adsorption, Diffusion And Dissociation Mechanism On Gas-solid Surface Interaction

The dynamics of gas-solid surface interaction is arousing more and more interest in thecommunity of physicists and chemists. Whether multi-phase catalysis or colloid catalyzedinteraction is relating to the interaction between reactants as well as between reactant andcatalyzer surface. Therefore, the systemic study on the interaction between atom, moleculeand catalyzer surface, especially the interaction with active sites in theory is necessary. Somerepresentative atoms and molecules are selected to study the kinetic behavior of adsorptionand diffusion on the flat and defective surfaces by employing five-parameter Morse potentialand improved extended LEPS potential in this dissertation. The main content in this paper isas follows:Chapter 1: the significance, status in quo and methods of the investigation in gas-solidsurfaces interaction are expatiated. On the other hand the theory methods and cluster modesused in this work are introduced in detail.Chapter 2: we study the adsorption and diffusion of H, N and O atoms on Fe surfaceswhich belong to BCC lattice by using 5-parameter Morse potential (5-MP) method.Chapter 3: we investigate the characteristic of adsorption and dissociation for COmolecules on Fe surfaces by extended LEPS method.The main production of this paper:1. The adsorption and diffusion of H on Fe low index surfaces and Fe (211) high indexsurface were investigated with 5-MP in detail. For H-Fe(110) system, the adsorption sites ofH atoms were always the focus among the experimental methods. Our calculated resultsshowed that H atom located in quasi-3-fold site (H3) at low coverage. We also excluded thepossibility of H adsorption on long bridge site (LB). Fe(211) is an open surface withridge-and-trough structure. The step of this surface is much shorter than other step surfaces.Our calculated results showed that there were two stable adsorption sites (H3 and LB), but wespeculated H atom tended to occupy quasi-3-fold site in the actual adsorption process becauseof the influence of site density and space screen effect.[Chemical Journal of Chinese University. Vol.27, No.2,297~302]2. In spite of the numerous investigations in the N/Fe system, there are still somecontroversy and unobtainable information concerning: there have been no exact structuralanalysis of N/Fe (111) by experiment, there is controversy about the adsorption sites of N/Fe(110). The absorption and diffusion of N on Fe low index surfaces were investigated with5-MP in detail. All critical characteristics of the system were obtained, such as adsorption site,adsorption geometry, binding energy, eigenvalues for vibration, etc. The calculated resultsshow that N atom is located at the fourfold hollow site of the intact Fe(100) surface. And onFe(110)surface, N atom trends to occupy quasi-3-fold site without exception. However, themost stable site on Fe(111) surface is approximate bridge site.[Acta Chim Sini. 2005, Vol.63, No.20, 1889~1894]3. About the system of O/Fe, experimental scientists have made plenty of investigationsabout the ascertainment of adsorption states, but large divarication exists between them.Furthermore, the theoretical investigations are rare. We studied the adsorption and diffusion ofO on Fe low index surfaces and (211) high index surface with 5-MP again. On Fe (110), Oatom adsorbed preferentially on pseudo-3-fold site;with the coverage increasing, LB siteswere also occupied. On Fe (211) surface, we also speculated O atom tended to occupyquasi-3-fold site in the actual adsorption process because of the influence of site density andspace screen effect.[This paper has been submitted to Chinese J. Struct. Chem.]4. The extended LEPS of CO-Fe system are constructed by means of 5-MP (the 5-ParameterMorse potential). Both the adsorption and dissociation of CO molecule on Fe surfaces areinvestigated with extended LEPS in detail. All critical characteristics of the system that weobtained, such as adsorption geometry, binding energy, eigenvalues for vibration, etc. are ingood agreement with the experimental results. The calculation results show that: On Fe(100)surface, at low coverage, CO molecules adsorb in four-fold hollow site with unusual lowstretching frequency of 1239cm-1. With the increasing coverage, CO molecules adsorbperpendicularly in sequence in the bridge and top sites with the frequency of 1933cm-1 and2038cm-1. Our calculation results support the investigation of three molecular states α (α1,α2,α3)obtained in experiment definitely. Meanwhile, We analyze the dissociation mechanism of theCO molecule on the surface, and obtain the dissociation trans-state, with the dissociationpotential barrier of 0.2eV. The calculation results show that, at low coverage, the adsorptionstate in four-fold hollow site is a metastable state, viz., the precursor state of dissocation. OnFe(110) surface, CO molecules steadily adsorb in the top site. At low coverage, CO moleculesfirstly adsorb in the shallow hollow site, then sequently adsorb in the top and deep hollowsites with the increasing coverage.[One of the paper has been submitted to J.Phys.Chem.B]...