Relevance of IR Spectroscopy of Adsorbed CO for the Characterization of Heterogeneous Catalysts Containing Isolated Atoms

This Perspective discusses the characterization by infrared spectroscopy of CO adsorbed of isolated metal atoms, also referred to as single atom catalysts (SAC). The main difficulties encountered during the analysis are briefly discussed, e.g., band assignment, sample structural evolution, spectral corrections, and signal enhancement. Theoretical investigations by DFT stressed the high number of surface structures that may be considered for the support (e.g., crystal termination, partial reduction or not) and isolated metal atom (e.g., adsorbed or substituted, oxidized or not), still making site identification a challenge In addition, most DFT models do not incorporate surface hydroxyls, carbonates, or other adsorbates that are present on real materials. Cases regarding Rh-, Pd-, and Pt-based catalysts are presented in which IR has genuinely proven conclusive, in complement to other techniques, in terms of the nature of the metal phases present. Finally, recent contributions in which the exact nature of the phase present is still open or questionable are discussed, the aim of the present work being to stimulate more constructive exchanges in the application of IR spectroscopy and the interpretation of spectra adsorbed species.

Automated summary

This Perspective discusses the challenges of characterizing CO adsorbed on isolated metal atoms using infrared spectroscopy, and highlights the theoretical investigations and practical cases that contribute to a better understanding of metal phases properties.