Density-functional Theory Study The Selective Oxidation Of Ethylene On Some Metal Surfaces

The reaction of ethylene epoxidation to ethylene oxide is an important industrial reaction. In this thesis, the interaction of adsorbed molecular with different metal surface and the mechanism of ethylene epoxidation have been investigated by the ab initio pseudopotential total energy method based on density functional theory.The density functional theory (DFT) is the appreciable method for the metallic systems, which has been rapidly developed recently. So the DFT method has been performed in all of our studies. Up to date, cluster models are often used to simulate the metallic surfaces because of the convenience, and the structures of the substrate are mostly fixed at the ideal position as that of the bulk without considering the relaxation. This is not agreed with the experimental situations. Previous study has obtained that the influence of the relaxation to the metallic electronic properties is significant. The effect of the relaxation on the adsorption process has also been studied in previous study. It is found that the adsorption properties are greatly affected by the relaxation. So in this thesis, the supercell model is employed to simulate the metallic suface, which can consider the relaxation effect adequately.In this thesis, the adsorption characteristics of the possible intermediates in many heterogeneous reactions and the adsorposition mechanism of O atom on some metal surfaces have been systematically investigated by DFT-GGA method and periodical slab model. At the same time, the reaction of ethylene epoxidation on different metal surfaces has been studied in detail. In order to understand the general rule and nature of the interaction between adsorbed species and metallic surfaces, the equilibrium structure, the preferred adsorption site, the adsorption strength and the activity of adsorbed species have been systemically studied. The main conclusions are summarized as follow.1. The calculated results of the adsorption of O atom on Cu(111),Ag(111),Au(111),Pt(111),Rh(111) and Mo(100)surfaces by the slab model indicate that the order of the adsorption energies is: Au(111)