Probing configuration of single atom catalysts via CO adsorption: Pt/CeO₂(111)

Single Pt atoms adsorbed on CeO₂(111) have been shown to produce a promising catalyst for a number of reactions. The question whether the Pt is adsorbed on the CeO₂(111) surface at an oxygen vacancy site (Pt_ads) or that it is embedded in the subsurface of CeO₂(111) (Pt_emb) is still under debate. Using density functional theory calculations, we studied the stretching frequency of carbon monoxide adsorbed on to a single Pt atom supported on the CeO₂(111) in the two configurations mentioned above. We find the C-O stretching frequency to be 2015 cm^-1 and 2098 cm^-1 for the CO molecule adsorbed at Pt_emb and Pt_ads, respectively, suggesting that CO binds more strongly on Pt_ads than on Pt_emd. In fact, we find that the binding energy of CO on Pt_ads and Pt_emb are -0.963 eV and -0.64 eV, respectively. These results are serving as the basis for identifying the active sites in experiments being carried out at the Liu lab at UCF. We will present calculated infrared spectra and details of the electronic structure of the local environment for the Pt sites in question. We will also discuss the broader implications of our findings vis-à-vis the identification of active sites in oxide supported single atom catalysts.