Figure 15.

In situ IR spectroscopy of adsorbed CO allows the discrimination of adsorption sites at Pt NPs and subnanometric clusters. (a) DRIFT spectra of CO adsorbed at room temperature and at the maximum coverage on four freshly reduced Pt/Al₂O₃ samples differing in Pt loading and particle size (see legend). The spectra are normalized to the intensity of the low-frequency band. The high frequency band corresponds to CO molecules adsorbed on well-coordinated (WC) Pt sites, while the band at lower frequency is assigned to CO molecules interacting with under-coordinated (UC) Pt sites. Adapted with permission from ref (237). Copyright 2016 American Chemical Society. (b) IR spectra of CO adsorbed at room temperature and at the saturation coverage on a 5 wt % Pt/Al₂O₃ sample with an average particle size of 1.4 ± 0.4 nm, with CO dosed either in the gas-phase or in solution (cyclohexane as solvent). The IR spectrum of CO adsorbed from the gas phase shows an additional band at lower frequency, which is ascribed to highly under-coordinated Pt sites (HUC). (c) Sequence of IR spectra collected upon increasing the CO coverage (from brown to red) on the same 5 wt % Pt/Al₂O₃ sample discussed in (b). The data reported in (b and c) are reproduced from ref (242) with permission. Copyright 2022 Royal Society of Chemistry.