The aim of the present thesis was to investigate the catalytic CO oxidation under high vacuum conditions using in situ photoemission electron microscopy (PEEM), mass spectrometry (MS) and X-ray photoelectron spectroscopy (XPS). Since the single crystal approach does not fully cover all the effects of catalysts consisting of oxide supported precious metal nanoparticles, different models have been selected, which better represent the properties of these real catalysts.
The CO oxidation has been studied on a polycrystalline palladium foil consisting of m-sized domains of different (hkl) orientation and alumina supported palladium and PdO powders.
During experiments on the palladium foil an oxide layer, formed by bulk-segregated impurities, and its effect on the reaction kinetics was studied. The foil was treated with oxygen at elevated temperatures and consecutive kinetic measurements have shown a decrease in the activity towards the catalytic CO oxidation with increasing oxidizing temperatures. The XPS spectra of the oxidized sample gave evidence for silicon segregation from the bulk to the surface and subsequent silicon oxide formation with increasing oxidizing temperature. The effective activation energy for these two processes has been determined from the Arrhenius plot of the XPS Si 2p peak areas to be 0.27 eV. The influence of the surface morphology on the catalytic CO oxidation was studied on the alumina supported palladium powder. Kinetic measurements were performed and both global and spatially-resolved local kinetic diagrams using MS and PEEM, respectively, have been constructed.
The phase diagrams for the palladium powder, palladium foil after annealing and palladium foil after additional sputtering have been compared to each other with the conclusion, that the defect rich surfaces are more tolerant towards CO poisoning. The role of PdO in the CO oxidation reaction was studied on the alumina supported PdO powder. A correlation between the PdO contribution and the activity in CO oxidation was observed: with increasing amount of PdO in the sample composition the catalytic activity towards the CO oxidation reaction is suppressed.