Regensburg 2025 – scientific programme

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O: Fachverband Oberflächenphysik

O 39: Oxides and Insulator Surfaces: Adsorption and Reaction of Small Molecules I

O 39.1: Talk

Tuesday, March 18, 2025, 14:00–14:15, H4

Instrumental Innovations for Model Single-Atom Catalysis — •Jiří Pavelec, David Rath, Chunlei Wang, Nail Barama, Panukorn Sombut, Matthias Meier, Michael Schmid, Ulrike Diebold, and Gareth S. Parkinson — TU Wien, Vienna, Austria

Single-atom catalysts (SACs) reduce reliance on precious materials by using individual atoms as active sites. Infrared spectroscopy of adsorbed CO is widely used to probe these sites, but spectral interpretation and charge-state assignment remain debated. Surface science studies of model SACs could provide valuable benchmarks, but progress has been hindered by a lack of model systems and challenges in detecting low coverages of intermediates.

Here, I introduce a novel approach to infrared reflection absorption spectroscopy (IRAS) that adjusts the incidence angle, which resolves signal-to-noise issues on dielectrics [1]. As a case study, we investigated CO titration of rhodium-based SACs on a Fe3O4(001) support. The spectra reveal Rh1CO monocarbonyls as the dominant species. Meanwhile, the Rh1(CO)2 gem-dicarbonyl arises solely from the breakup of minority Rh2 dimers, as confirmed by STM movies and theoretical modeling [2]. Though less prevalent in our UHV study, Rh1(CO)2 may play a critical role under realistic conditions.

Combining advancements in IRAS with a detailed understanding of model SACs provides valuable benchmarks for theoretical studies and spectral references for researchers working with less-defined, high-surface-area powder catalysts. [1] D. Rath et al., Rev. Sci. Instrum. 95, (2024). [2] C. Wang et al., Angew. Chem. Int. Ed. 63, (2024).

Keywords: Infrared Reflection-Absorption Spectroscopy; Instrument Development; Single-Atom Catalysis; Carbon Monoxide Adsorption; Scanning Tunneling Microscopy