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.

Reusable and Flexible Heterogeneous Catalyst for Reduction of TNT by Pd Nanocube Decorated ZnO Nanolayers onto Electrospun Polymeric Nanofibers

“…Additionally, oxidized PdO peaks were also detected at 337.3‐337.6 range and 342.4‐342.6 eV range, respectively. Latter XPS values are expected valence state peaks of PdO and consistent with the literature values . After the catalytic experiments, even though the amount of the total Pd is relatively decreased, oxidated Pd amount seems relatively enhanced.…”

“…XPS data also proved that there is no remarkable decrase in Pd concentration after the catalytic reduction. XRD pattern (Figure [64] After the catalytic experiments, even though the amount of the total Pd is relatively decreased, oxidated Pd amount seems relatively enhanced. Quantitative results revealed that % 0.96 Pd is available before the catalytic degradation experiment which decreased to % 0.79 after the degradation ( Figure S12c).…”

Palladium Oxide Nanoparticles: Preparation, Characterization and Catalytic Activity Evaluation

“…The peak at 337.4 eV can be confidently attributed to PdO, according to our previous investigations on palladium surfaces [42], even if an upshift is observed with respect to the value of 336.9 eV. This shift, generally shown by nanoparticles with respect to the bulk [43], can be explained on the basis of a quantic confinement. The other peak at 339.0 eV could be attributed to Pd(OH) 2 , in analogy with that observed at 338.4 eV [42], or to a species of hydrate palladium oxide.…”

Characterization techniques for nanoparticles: comparison and complementarity upon studying nanoparticle properties

“…The authors mention that additional screening with techniques such as mass spectrometry was needed for a more complete picture of the catalytic process (oxidation of 2-propanol by PdO NPs in this case) in such reactions. 87 2.2 Additional techniques for the characterization of the structure, composition and other main NP properties…”