Behavior of Supported Palladium Oxide Nanoparticles under Reaction Conditions, Studied with near Ambient Pressure XPS

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• 作者：Astrid J眉rgensen ; Niels Heutz ; Hannes Raschke ; Klaus Merz ; Roland Hergenr枚der
• 刊名：Analytical Chemistry
• 出版年：2015
• 出版时间：August 4, 2015
• 年：2015
• 卷：87
• 期：15
• 页码：7848-7856
• 全文大小：457K
• ISSN：1520-6882

文摘

Near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is a promising method to close the 鈥減ressure gap鈥? 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 掳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 掳C, and the oxidation of 2-propanol to carboxylates only occurs in the presence of oxygen above 90 掳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.