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Projekt Druckansicht

In-Situ Charakterisierung der Metall-Träger-Wechselwirkung und Studie zur Struktur-Reaktivitätsbeziehung in der Katalyse

Antragsteller Dr. Yuemin Wang
Fachliche Zuordnung Physikalische Chemie von Festkörpern und Oberflächen, Materialcharakterisierung
Förderung Förderung von 2018 bis 2021
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 392178740
 
Erstellungsjahr 2023

Zusammenfassung der Projektergebnisse

In this collaborative project, we performed systematic spectroscopic investigations on the surface structure and active sites of selected metal/oxide systems in the form of both welldefined single crystals and differently shaped nanoparticles, with the special focus on pristine and metal-decorated ceria surfaces. The spectroscopic characterizations (polarizationresolved IRRAS on single crystals, IR transmission on powders, XPS, NEXAFS) were complemented by microscopic methods (ETEM/STEM-Nanoreactor) and DFT calculations. The combined results allowed to gain detailed insight into the structural, electronic and reactive properties of the nanostructured metal/oxide catalysts based on comprehensive reference data acquired for various well-defined model systems via a thorough surface science study. With respect to bare oxide systems, we focused on the surface structure and activity of ceria catalysts, in particular the highly active polar (110) surface. A two-step mechanism was proposed for the surface polarity compensation of cubic ceria nanoparticles, where an initial O-terminated (2x2) reconstruction is followed by a severe refaceting at elevated temperatures to yield {111}-dominated configurations. This substantial surface restructuring is accompanied by the formation of under-coordinated defect sites and O vacancies. Our results provided indepth information on the structure-reactivity relationship for low-temperature CO oxidation over ceria nanocubes. In addition, we have investigated the interaction between various molecules (especially CO, O2, and H2O) and oxide surfaces. Importantly, the water dissociation was found to process at the Ce3+−Ov sites of reduced ceria surfaces. For metal/oxide systems, we focused on the structural and electronic evolution of both metal species and ceria support under different conditions. In the case of Cu/CeO2, the combined experimental and theoretical results allowed us to identify the atomic structure of ultrafine copper clusters (1.0-1.5 nm) dispersed on ceria support and to quantitatively describe the catalytically active copper-ceria interfacial perimeter at atomic scale. These findings represent a major breakthrough in this area. The Cu clusters exist mainly in a bilayer geometry (top layer Cu0 and bottom layer Cu+), where the low-temperature water-gas shift reaction occurs at the interfacial Cu+−Ov−Ce3+ sites via a cooperative mechanism. We have further studied the structural and electronic changes of ceria-supported Pt species (nanoparticles, clusters, single atoms) in reactive gases at different temperatures. It was found that the charge state and size of Pt species can be engineered in a controlled manner depending on the oxidation/reduction conditions. Furthermore, our results revealed significant modification of the ceria surface resulting from the strong interaction with Pt. These results provided solid basis for mechanistic understanding of CO oxidation over Pt/ceria catalysts. Finally, we have extended the fundamental investigations to bimetallic PdCu single nanoparticles. The comprehensive results showed a precise tuning of the crystal-phase (wellordered B2 vs. disordered fcc) of bimetallic PdCu catalysts at the single-nanoparticle scale. The atomic structure of active sites for acetylene hydrogenation over B2 single particle was quantitatively described. These results offer a new route to precisely tailor the geometric and electronic structures of bimetallic particles for quantifying the structure−reactivity relationship at atomic accuracy.

Projektbezogene Publikationen (Auswahl)

 
 

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