In this PhD thesis the interaction of gasious reactands with surfaces of model catalysts was investigated. Especially the influence of the surface morphology and electronic structure on the adsorption and reaction of the gases was of interest. Two model systems were studied: First the adsorption of carbon monoxide on various gold surfaces as a model system for novel carbon monoxide oxidation catalysts. The second system consisted the adsorption and reaction of carbon monoxide, oxygen and methyl alcohol on mono- and bimetallic cobalt-palladium nanoparticles as a model for Fischer-Tropsch catalysts