This thesis describes the development of a combined high-pressure/ultrahigh-vacuum flow reactor for the study of model catalysts by means of surface x-ray diffraction and grazing incidence small... Show moreThis thesis describes the development of a combined high-pressure/ultrahigh-vacuum flow reactor for the study of model catalysts by means of surface x-ray diffraction and grazing incidence small angle scattering. The system was used to measure a stability diagram for the different oxide phases (surface oxide, bulk-like oxides) that exist on Pd(100) during catalytic CO oxidation at near ambient pressures. As soon as an oxide was present the reactivity of the surface was found to be mass transfer limited by the flux of CO molecules reaching the surface. Experiments on spontaneous reaction oscillations of the CO oxidation rate on Pd(100) reveal that a high density of steps strongly alters the stability of the thin, catalytically active palladium oxide film. It is shown that stabilization of the metal, caused by the steps and consequent destabilization of the oxide, is at the heart of the well-known reaction rate oscillations exhibited during CO oxidation at atmospheric pressure. Lastly reaction oscillations on supported Pd nanoparticles are shown to be accompanied by shape changes of the particles consistent with the formation and removal of a thin palladium oxide film on the particles. Show less
