Synchrotron-based In Situ Electron Spectroscopy Applied to Oxide Formation and Catalysis

In this thesis, in situ ambient pressure X-ray photoelectron spectroscopy has been used to address chemical reactions on surfaces. The presented work aims at the investigation of the relation between pressure and adsorbate surface structures during catalytic reactions. Various materials have been investigated ranging from single crystal surfaces to an immobilized homogeneous catalyst in an effort to apply the surface science methodology to materials which more closely resembles working catalysts.

Adsorbate structures in ultrahigh vacuum conditions have been studied for decades and are well known. However, it is unclear how these structures relate to those in the mbar regime. Here, I investigate this relation by two reactions on single crystals: the oxidation of CO over Ir(111) and the Sonogashira cross-coupling over Au(111). The results show that the adsorbate structure in the two pressure regimes can be related. In fact, knowledge of the ultrahigh vacuum structures is vital for an understanding of the surface structures in the mbar regime.

Ultrathin oxides are often employed as model systems to mimic the support-particle interactions of a working catalyst. One such oxide is the bilayer FeO(111) grown atop a Pt(111) surface. In this thesis, an O-enriched trilayer phase of this film has been investigated and its spectroscopic fingerprint has been characterized unambiguously. It is shown that the trilayer has a high affinity for water dissociation. This concept is expanded upon by the growth of a stepped FeO film which contains FeO-FeO steps. These steps share the O-Fe-O structural motif of the trilayer film and also have an affinity for water splitting. Hence, the introduction of an interfacial O atom heavily modifies the properties of the oxide surface.

Immobilization of homogeneous catalysts has the possibility of combining their high yield and selectivity with the high throughput of heterogeneous catalysis. To this end, a homogeneous catalyst, a Mn(III)-salen complex, was immobilized and characterized on an Au(111) support. The oxidative capabilities of the compound remain after the immobilization even if the liquid environment is exchanged for gas phase reactants.