CO vibrational frequencies as probe of Pt local environment in Pt₁/CeO₂ single atom catalysts: First principles investigations

Singly dispersed Pt atoms on CeO₂ surfaces (Pt₁/CeO₂) have been proposed as effective catalysts for several reactions. Knowledge of the local environment of the Pt atom that would enable rational design of the catalyst is still under debate. Under ambient conditions, experimental information on the local atomic geometry of the catalyst relies on the observed vibrational frequencies of adsorbates. Using density functional theory, we have examined the adsorption and vibrational characteristics of CO on Pt₁/CeO₂ in the presences of vacancies, step edges, terraces of CeO₂(111) and CeO₂(110) with the aim to build a vibrational-signature database. We find that the stretching frequency of the CO molecule adsorbed at Pt atoms depends strongly on the coordination of Pt to neighboring O atoms, i.e., higher such coordination results in higher stretching frequency. Such dependence is not clearly seen for the coordination of Pt to neighboring Ce atoms. The database of CO vibrational frequencies together with possible local environment descriptor are used to interpret experimental data taken in this joint theoretical and experimental collaboration from which the nature of the single Pt atom site or ceria is identified.