Study Of The Adsorption And Interaction Of Oxygen And Carbon Monoxide On Co(0001) Surface Using Scanning Tunneling Microscope

Fischer-Tropsch synthesis as one of the most important reactions in heterogeneous catalysis has received extensive attention from researchers.However,the Fischer-Tropsch reaction process is extremely complex,and the products are widely distributed,which makes it difficult for both industrial production and basic research to become a major difficulty in scientific research.Cobalt-based catalysts are very promising catalysts in Fischer-Tropsch synthesis reactions due to their outstanding catalytic properties and low economic cost.Among them,Co（0001）single crystal is favored in the basic research of model catalysis because of its good thermal stability,easy preparation,and good Fischer-Tropsch activity.The activation of O₂ on the surface is a crucial process of heterogeneous catalysis and material oxidation.The interaction between oxygen and the metal surface has an important impact on the catalytic activity and stability of the reaction.Basic research on well-defined metal surfaces using ultra-high vacuum technology is of great significance to the mechanism,energetics and kinetics of O₂ adsorption and dissociation.In the Fischer-Tropsch synthesis reaction,the oxidation of the catalyst surface is generally considered to cause the deactivation of the catalytic reaction.The adsorption and activation of O atoms on the surface is also an important process in the Fischer-Tropsch reaction.In addition,the dissociation and activation of CO,as the first step in the Fischer-Tropsch synthesis,is also one of the key reaction steps,which has an immeasurable influence on the Fischer-Tropsch synthesis reaction,and the oxidation of CO is one of the most studied reactions in heterogeneous oxidation.It has important applications in the protection of the environment,Therefore,research on low-temperature oxidation of CO is indispensable for green development.In view of this,this paper uses scanning tunneling microscope（STM）combined with low energy electron diffraction（LEED）and temperature programmed desorption（TPD）technology under ultra-high vacuum environment to systematically study the adsorption behavior and co-adsorption interaction of O₂ and CO on the surface of single crystal Co（0001）..The main experimental content and research results of this paper are as follows:1.At different temperatures,the oxygen species and its adsorption morphology formed by O₂ on the Co（0001）surface were systematically studied.The experimental results show that the adsorption of O₂ on the surface of Co（0001）is closely related to the adsorption temperature and amount:at room temperature,a small amount of O₂ adsorbed on the surface of Co（0001）will react quickly,forming oxide species which is"cotton-like"fluffy but non-fine structure.In the temperature range of 120 K～250 K,an appropriate amount of O₂（less than 0.25 ML）will form an ordered p（2×2）-O structure on the Co（0001）surface.Below 120K,we have observed for the first time that O₂ forms a new"dumbbell-shaped"species on the Co（0001）surface,which is speculated to be the oxygen atom pair formed by the dissociation of O₂ on the surface.At any temperature,excessive O₂ adsorption will cause irreversible peroxidation of the surface into a disordered structure.2.STM and LEED were used to study the adsorption and thermal reaction of CO on the Co（0001）surface.At low temperatures,CO forms an ordered structure of（√3×√3）R30-CO on the surface of Co（0001）and can exist stably at room temperature.When the temperature is increased to 415 K,CO reacts with Co（0001）to form carbon species and oxygen species on surface.3.Study the co-adsorption behavior of CO and O₂ on Co（0001）surface using STM and TPD.CO not oxidized by the p（2×2）-O formed on Co（0001）surface in the temperature range of 120 K～250 K,and the interaction between CO and the p（2×2）-O of Co（0001）is extremely weak:The STM image of the co-adsorbed surface becomes disordered,As time goes by and keeping the temperature constant,the surface gradually recovers from disorder to an ordered p（2×2）-O surface.The TPD experiment results also show that the CO desorption rate is different at different temperatures.Compared with the initial surface state,the surface after CO desorption has a larger range of ordered 2×2 structure,indicating that the adsorption of CO can promote the formation of p（2×2）-O.