Combining STM, RAIRS and TPD to Decipher the Dispersion and Interactions Between Active Sites in RhCu Single-Atom Alloys

Single-atom alloys are a new class of heterogeneous catalyst in which trace amounts of metal dopants exist as individual, isolated sites in a host metal. In this study, we examine RhCu, a new single-atom alloy with a combination of scanning tunneling microscopy, reflectance absorption infrared spectroscopy, and temperature programed desorption to understand the atomic structure of the alloy and correlate this with the behavior of CO, a common probe molecule. We find that Rh alloys into Cu(111) preferentially from step edges. As such, step density plays an important role in the vibrational structure of CO on isolated Rh sites. We find that atomically dispersed Rh sites can be close enough together to have dipole-dipole coupling interactions. Together, this combined experimental approach enables us to understand the alloying mechanism of Rh with Cu and yields important signatures of the atomic sites that are useful in benchmarking CO vibrational data.