Compound Formation in Model Catalysts

Abstract: In this thesis we have performed a systematic atomic scale characterization of model catalysts under pressures ranging from UHV to atmospheric ambient. By using a unique approach, linking UHV and high pressures studies by combining traditional electron based techniques with novel high pressure in situ probes and ab initio calculations, the surface structure of the different model catalysts could be determined under a wide range of conditions, spanning more than ten orders of magnitude in pressure. The complexity of the model systems were gradually increased, from a ¨flat" low index single crystal surface, to more complex "stepped" vicinal surfaces, and finally dispersed nanoparticles on an oxide support. By using in situ diffraction and spectroscopy techniques, we have followed the oxidation and reduction process, as well as carbide formation, on Pd nanoparticles deposited on oxide supports. In order to determine the reactivity of the different surface structures, in situ measurements were performed on single crystal surfaces under reaction conditions. By using surface x-ray diffraction we could correlate an increase in the production of CO2 with the formation of oxides.