Multi-Technique Characterization of Rhodium Single Atoms as Dicarbonyls on TiO₂(110)

Abstract

Single-atom catalysts (SACs) have garnered significant attention in recent years due to their potential to minimize noble metal usage by isolating active atoms on metal (oxide) surfaces. However, stabilizing these single atoms remains a major challenge. Ligands, such as carbon monoxide, can stabilize single atoms by transforming them into surface-bound metal complexes, closely resembling the well-defined species in homogeneous catalysis. In this contribution, we present a comprehensive characterization of a ligand-stabilized single atom: a rhodium gem-dicarbonyl (Rh(CO)2) bound to rutile TiO2(110). Using XPS, TPD, scanning probe, and a newly developed IRRAS apparatus, we provide a detailed analysis of these sites. Our findings are contextualized through comparisons with theoretical models, containing both established DFT as well as newly developed embedding methods, and insights from powder catalyst studies in the literature. This work demonstrates that multi-technique approaches are essential for the accurate characterization of single-atom catalysts, offering a deeper understanding of their structure and stability. ME acknowledges funding from the EU Marie Skłodowska-Curie Actions of Horizon-MSCA-2022-PF-01 (Project 101103731 - SCI-PHI).