Visualization of Surfaces of Pt and Ni Model Catalysts in Reactive Environments Using Ambient Pressure High Temperature Scanning Tunneling Microscopy and Understanding the Restructurings of Surfaces of Model Metal Catalysts under Reaction Conditions at Near Ambient Pressure

Abstract

Catalysis science has emerged as one of the crucial fields in energy science responsible for a sustainable energy world. Fundamental study of surface structures of catalysts at atomic scale under reaction conditions or during catalysis is critical in understanding catalytic mechanisms because a single catalysis event is performed on a specific site comprising one or several atoms with appropriate geometric and electronic structures. Ambient pressure high temperature scanning tunneling microscopy (APHT-STM) can identify structural details of catalyst surfaces at nano or atomic level when catalysts are under reaction conditions or during catalysis. By using APHT-STM, structures of the step edge of Pt(111) and the surface of Ni(557) were studied under reaction conditions. For Pt(111) model catalyst in a CO environment at a pressure of 0.1 Torr or higher, Pt atoms at step edges exhibit a dynamic restructuring. They form kink sites at 0.1 Torr and create nanoclusters near the step edges at 1–10 Torr within 1–2 min. A pressure-dependent restructuring of step edges of Pt(111) was revealed. In in situ studies of the vicinal surface, Ni(557) shows a pressure-dependent restructuring in CO, resulting from reorganization of all surface atoms. Nickel nanoclusters are formed on the whole surface, consistent with the increased coverage of CO chemisorbed on the Ni surface at a relatively higher pressure. Restructuring of atoms at a step edge of terraces of a flat surface and all atoms of a vicinal surface suggest the dynamic nature of model metal catalyst surfaces. Essentially, the surface structure of a metal catalyst in a reactive environment is determined by its reaction or catalysis condition.