Surface structure and catalytic activity of Pd and Fe oxide surfaces and thin films

Sammanfattning: The present work is devoted to atomic scale structural studies of the surfaces of model heterogeneous catalysts relevant to oxidation reactions. A novel approach using high-energy surface X-ray diffraction combined with mass-spectrometry measurements is employed to perform in situ structural characterization of Pd(100) and Pd(553) single crystal surfaces acting as catalysts in the process of CO oxidation under semirealistic conditions. The experimental approach greatly facilitates the understanding of surface X-ray diffraction and improves significantly the data collection speed. The phases forming on the surfaces in gas mixtures with different relative concentrations of CO and O2 are determined and are associated to the catalytic activity. The corresponding structural models are proposed. A combination of complementary experimental techniques, including conventional surface X-ray diffraction, X-ray photoelectron spectroscopy, Auger electron spectroscopy, low-energy electron diffraction, scanning tunneling microscopy, temperature programmed desorption spectroscopy and reflection absorption infrared spectroscopy as well as theoretical calculations, is employed to study in detail the structural and NO adsorption properties of iron oxide ultrathin films grown on Ag(100) and Ag(111) single crystal substrates. Structural models of different phases growing on the surfaces under different preparation conditions are presented. The atomic structural model of a one-layer thick FeO(111) film grown on Ag(100) is proposed. The NO adsorption properties of one-layer thick FeO(111) films on both substrates are investigated and compared to the NO adsorption properties of FeO(111)/Pt(111) reported in the literature. The observed differences are discussed in detail. The results obtained for CO oxidation over Pd model catalysts allow for an increased understanding of the processes occurring on the surface of a working catalyst and the connection between the catalytic properties and the surface structure. The performed studies of iron oxide ultrathin films grown on silver substrates provide insight into how the structural properties are related to the adsorption properties of such systems and knowledge important for the design of novel catalytic materials with improved qualities.