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 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.The main content in this paper is as follows:In chapter 1. the elementary theory for calculation in this paper and the low- index surface cluster models are given.The adsorption and diffusion for O-Pt low-index surface and stepped surface systems entirely are investigated by constructing atom-solid surface interaction potential named five parameters Morse potential (5-MP for short) in chapter 2.The analytical potential of gaseous diatom molecule interaction system, i.e. extended LEPS potential has been constructed. And C2-Pt systems is studied in chapter 3.The main research fruit in this work is as follows:1. The adsorption system of O atom on the Pt low-index surfaces. The vibration frequencies are easy to measure in experiments, and are the most important critical characteritics to ascertain the adsorption sites and states. However, the experiments are made under different conditions, and mostly obtain bitty information. Moreover, the problem on the attribution of frequencies is usually inconsistent. The theoretical calculated results show that oxygen atom can only adsorb in the four-fold hollow site on Pt (100). On (111) surface, there exists adsorption state of oxygen atom in the three-fold hollow site, which produce vertical vibrational frequency 58.10meV considering as special frequency for the three-fold adsorption state of O-Pt(111) system. O adsorbs in the three-fold hollow site and the long-bridge site on the (110) missing-row reconstruction surface. We ulteriorly analyze heredity and variation of vibrational fingerprint properties of three-hold state on Pt(111).Then we can confirm that experimental data about 59.49meV and 40.90meV on the (110) missing-row reconstruction surface belong to vertical vibrations of adsorption states, which are produced by oxygen atom on three-hold hollow site and long-bridge site, respectively. Calculation results not only reproduced the vibration frequencies but also ascertained adsorption sites and states.This paper has been published on Acta Phys.-Chim.Sin., 2004, 20(9), 1123~1128.2. The adsorption systems of O atom on Pt stepped surface. We study two kinds of stepped surfaces. The theoretical calculated results about O/Pt(s)-[n(111)×(100)] systems mainly including O-Pt(311), O-Pt(211) and O-Pt(533) systems draw some conclusions. The four-fold site behind a (111) step that a oxygen atom binds in corresponds to the most stable statenamed β2 -state. And the three-fold state near the four-fold site on a (111) terrace is annihilated,then the other three-fold sites correspond to adsorption states named β1-state. In addition thelength of the (111) terrace has a bit of the effect on the four-fold state. Moreover, we investigate the adsorption properties of a series of O-Pt(s)[n(111)×(111)] systems which emphasized O/Pt(331),O/Pt(221) and O/Pt(553) systems. And our results suggest that O atomadsorbs stably on the step. There are two types of atomic states (β1 and β2) in the adsorbedsystems, corresponding to the three-fold states and four-fold long-bridged state on the step respectively. Comparing with the former kind of stepped surface systems, the lengths of (111) terrace affect weakly the properties of all critical points in this kind of systems. The researches about O adsorbing on Pt stepped surface systems carried out by 5-MP method can make up for the experimental deficient information and confirm the adsorption sites which can be not ascertained with experimental methods. The calculation results approve of the experimental view that the step on the surface is the active position in the catalyzed reaction.The one article has been published on Acta Phys.-Chim.Sin., 2004. 20(12), 1445~1450.The other one has been accepted by Chinese Journal of Structural Chemistry and finalized a manuscript.3. The system of O2 on the Pt low-index surfaces. The extended LEPS of O2-Pt single crystal plane systems is constructed by means of 5-MP(the 5-parameter Morse potential). Bothadsorption and dissociation of O2 on Pt low index surfaces mainly including (111) and (110) reconstruction surfaces are investigated with extended LEPS in detail. We obtain all critical characteristics of the system, such as adsorption geometry, binding energy, eigenvalues for vibration, etc. Our calculated results suggest the dissociation of O2 on Pt(111) surface is difficult and surperoxo-like state exists likely. Meanwhile, we use the conceptions of the molecular dissociation limit and the surface dissociation distance to analyze the dissociation mechanisms of O2 on the two Pt surfaces. Moreover, the vibration frequencies of 860cm-1, 930cm-1, 1250cm-1 produced by O2 adsorbing on Pt(110) reconstruction surface are assigned logically on the basis of the molecular fingerprint properties.The paper has been contributed to Chinese Journal of Catalysis.