The Adsorption And Diffusion Of Gas On Transition Metal Surfaces

The interaction of gaseous atoms and molecules on transition metallic surfaces has been an attractive field in the heterogeneous catalytic reactions.Theoretical study on the atomistic level can not only help understand the interaction mechanism between the absorbent and metallic surface,but also obtain the kinetic information of surface adsorption and diffusion.Some representative atoms and molecule are selected to study the kinetic behavior of adsorption and diffusion on the flat and defective surfaces.The calculation results reproduced the obtained experimental data and predict some important information that has not been observed.The main contents of this work are as follows:The adsorption of H atoms on Ni(111) subsurface,Ni(211) and Ni(533) stepped surfaces were investigated by using the 5-parameter Morse potential(5-MP) of interaction between an atom and a metal surface cluster.The adsorption sites,adsorption geometry,binding energy, and eigenvibrational frequencies of H-Ni system were obtained.On the Ni(111) surface at low coverage,H atoms are adsorbed preferably on threefold hollow sites;with the coverage increasing,H atoms occupy the subsurface octahedral sites and tetrahedral sites.On the stepped surface Ni(211) and Ni(533),H atoms are adsorbed preferably on the fourfold hollow site at low coverage;with the coverage increasing,the H atoms also occupy on the threefold hollow site of the(111) terrace.The threefold sites near the fourfold sites are strongly affected by the height of the step and terrace.Moreover,we calculate the diffusion barriers of H atom and obtain the lowest energy pathway of diffusion on the surfaces.Molecular dynamic simulation the interaction of oxygen atom on low index platinum surfaces and stepped surface.The Sutton-Chen many-body potential is used for the Pt-Pt interaction;the Morse potential and Lennard-Jones potential are applied to describe the interaction of O-Pt,O-O respectively.A reasonable force field was built by using these potentials.The critical characteristics and trajectories of O-Pt system were obtained.It concluded that oxygen atom preferred to occupy the interface position between step and terrace.In addition,we study the interaction of molecular oxygen on Pt(100),(111),(110) by using the built force field,obtain the stable adsorption configuration of molecular oxygen on low index surfaces.On the Pt(100) surface,O₂ is vertical to the surface;On the Pt(111),the molecule is lying parallel to the surface by the configuration of H-B-H';On the Pt(110),O₂ is lying parallel to the surface by the configuration of H-LB,and induced the slightly surface reconstruction.