Probing Atomic Scale Structure and Catalytic Properties of Cobalt Oxide Model Catalysts

Cobalt oxides are known to be active catalysts for a number of chemical reactions, but very little is known about the atomic scale processes
responsible for the activity. The research presented in this thesis is focused on obtaining an atomic scale understanding of the chemistry of wellcharacterized
cobalt oxide model catalyst surfaces consisting of pristine and defective CoO and Co3O4 thin films with the (111) and (100)
terminations supported by Ag(100), Ir(100), and Au(111) single crystal surfaces. The structure and the adsorption properties of probe molecules
onto these cobalt oxide model catalyst surfaces are studied under ultra-high vacuum conditions using the interplay of X-ray photoemission
spectroscopy (XPS), scanning tunneling microscopy (STM), and low energy electron diffraction (LEED). Further, high pressure XPS (HPXPS)
is used to study the stability and phase transitions of the cobalt oxide model catalysts in more realistic gas environments. As a side project to
the work on cobalt oxide thin films the thesis gives a comprehensive spectroscopic picture of Ir(100) surface reconstructions and molecular
adsorption onto these surfaces.
The adsorption experiments of H2, CO, CO2, and H2O probe molecules give a detailed picture of the surface chemistry of Co oxide surfaces and
it is demonstrated that Co ions naturally found on the surface of Co3O4(111) and Co3O4(100) thin films or artificially created on the CoO(111)
surface are extremely important for chemical properties of the surface. Water dissociation, carbonate formation, weak adsorption of CO and
CO2 are examples of processes that only take place in the presence of Co surface ions. The work at more realistic gas pressures in the mbar
regime demonstrates that Co oxide thin films should be seen as dynamic films that easily change phase between the CoO and Co3O4 structure
in response to the gas composition.
To summarize, the work presented in this thesis is important for the fundamental understanding of cobalt oxide surfaces and their catalytic
properties, and hopefully, this fundamental understanding can be used to develop new and better cobalt oxide based catalysts.