title: Behavior of Supported Palladium Oxide Nanoparticles under Reaction Conditions, Studied with near Ambient Pressure XPS.
abstract: Near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is a promising method to close the "pressure gap", and thus, study the surface composition during heterogeneous reactions in situ. The specialized spectrometers necessary for this analytical technique have recently been adapted to operate with a conventional X-ray source, making it available for routine quantitative analysis in the laboratory. This is shown in the present in situ study of the partial oxidation of 2-propanol catalyzed with PdO nanoparticles supported on TiO2, which was investigated under reaction conditions as a function of gas composition (alcohol-to-oxygen ratio) and temperature. Exposure of the nanoparticles to 2-propanol at 30 °C leads to immediate partial reduction of the PdO, followed by a continuous reduction of the remaining PdO during heating. However, gaseous oxygen inhibits the reduction of PdO below 90 °C, and the oxidation of 2-propanol to carboxylates only occurs in the presence of oxygen above 90 °C. These results support the theory that metallic palladium is the active catalyst material, and they show that environmental conditions affect the nanoparticles and the reaction process significantly. The study also revealed challenges and limitations of this analytical method. Specifically, the intensity and fixed photon energy of a conventional X-ray source limit the spectral resolution and surface sensitivity of lab-based NAP-XPS, which affect precision and accuracy of the quantitative analysis.
authors.affiliation: †Leibniz Institut für Analytische Wissenschaften - ISAS - e.V., Bunsen-Kirchhoff-Straße 11, 44139 Dortmund, Germany.
authors.forename: Astrid
authors.initials: A
authors.lastname: Jürgensen
authors.affiliation: ‡Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie und Biochemie, Ruhr-Universität Bochum, Universitätsstraße 150, D-44801 Bochum, Germany.
authors.forename: Niels
authors.initials: N
authors.lastname: Heutz
authors.affiliation: †Leibniz Institut für Analytische Wissenschaften - ISAS - e.V., Bunsen-Kirchhoff-Straße 11, 44139 Dortmund, Germany.
authors.forename: Hannes
authors.initials: H
authors.lastname: Raschke
authors.affiliation: ‡Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie und Biochemie, Ruhr-Universität Bochum, Universitätsstraße 150, D-44801 Bochum, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Merz
authors.affiliation: †Leibniz Institut für Analytische Wissenschaften - ISAS - e.V., Bunsen-Kirchhoff-Straße 11, 44139 Dortmund, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Hergenröder