Recent advancements in technology have allowed us to apply the surface science approach to studying model catalysts in ambient (and often reaction) conditions. This can allow us to achieve a fundamental understanding of how a catalyst operates on an atomic and molecular level while the reaction is occurring. While the techniques used to achieve this are currently in use, implementation of these techniques, and especially the combination of ambient pressure techniques, still provide a challenge.
This thesis reports on the installation of an ambient pressure scanning tunnelling microscope (AP-STM), integrating it into an existing ultra-high vacuum (UHV)
system, and the design and construction of a gas system for the controlled inlet of high purity gas, used to create the ambient pressure environment. In addition, this was combined with X-ray photoelectron spectroscopy (AP-XPS) performed at various synchrotron facilities.
Through carefully controlled experiments we are able to combine the topographical imaging of the surface with AP-STM and the chemical analysis of the surface using APXPS, in reaction environments. While there are drawbacks, difficulties and considerations that need to be made when operating each of these techniques in reaction conditions, combined systems studies provide a ‘best of both worlds’ situation.
We focus on CO oxidation reaction, which is often seen as the primary model of
catalytic reactions. The model catalyst that is the main focus in this thesis is a cobalt oxide (CoOx) catalyst on a Pt(111) support, which has shown to be an excellent low-temperature CO oxidation catalyst. However, many of the fundamental questions of its operation remain unanswered. It was shown that when the CoOx was grown as a planar CoO nanoisland structure, and brought to reaction conditions, it converted to a three-dimensional structure in a mixed Co²⁺/Co³⁺ oxidation state, similar to Co₃O₄. The mechanics of the reaction on the surface are discussed, with potential adsorption sites for the CO on CoOx observed using both AP-STM and AP-XPS.
Summarised in this thesis is the results of these studies, which provide answers to
some of the questions to the operation of a CoOx model catalyst in reaction conditions, but also opens the way for further ambient pressure studies. This thesis serves as an example for future ambient pressure studies.