In situ structural studies and gas phase visualization of model catalysts at work

Sammanfattning: This thesis reports on in situ structural studies relevant to a catalytic surface during CO oxidation. The materials that have been studied are palladium, rhodium and an alloy of palladium and silver, with applications in emission cleaning by catalytic converters in vehicles. The studies are performed in situ allowing for observation of the gassurface interaction, which is essential when active catalysts are studied. Due to the vital role of the gas interaction for the surface structure, the gas phase in the vicinity of the catalytically active surface has also been studied in detail with spatial resolution using Planar Laser Induced Fluorescence, PLIF.In this thesis, the CO oxidation reaction has been investigated by a step-by-step approach where the oxidation and reduction of the surfaces have first been studied separately. The systematic in situ oxidation studies at high pressure(up to 1 mbar) of the Pd, Rh and Pd75Ag25 provide information about oxide growth and the chemical composition of oxide structures that may be present during CO oxidation. To achieve a better understanding of the CO oxidationreaction, the gas distribution over the surface has been studied. The results show that the pressure, gas flow and the reaction itself determine the gas phase interacting with the surface, which influences the surface structure. At highgas flow and pressure, a boundary layer is formed in the mass transfer limited regime of CO oxidation, in which the gas composition is completely different from the gas composition measured by the mass spectrometer at the outletof the reactor. If the conditions are oxygen rich, the CO concentration close to the surface, in this regime, is low. Nevertheless, a metallic Pd and Rh surface covered with chemisorbed oxygen is detected in a 1:1 ratio of CO and O2 at total pressures up to 1 mbar. Only in more oxygen rich conditions (4:1 of O2:CO), a surface oxide may be detected.