CO₂ Adsorption on Anatase TiO₂ (101) Surfaces in the Presence of Subnanometer Ag/Pt Clusters: Implications for CO₂ Photoreduction

Using density functional theory calculations, we show how CO₂ adsorption on perfect and reduced anatase TiO₂ (101) surfaces can be substantially modified by the presence of surface Ag and Pt octamer clusters. We find that adsorption is affected even at sites where the adsorbate is not in direct contact with the octamer, which we attribute to charge donation to CO₂ from the Ag/Pt-modified surface, as well as an electrostatic competition between attractive (Ti–O) and repulsive (Ti–C) interactions. In addition, TiO₂-supported Pt octamers offer key advantages that could be leveraged for CO₂ photoreduction, including providing additional stable adsorption sites for bent CO₂ species and facilitating charge transfer to aid in CO₂^– anion formation. Electronic structure analysis suggests these factors arise primarily from the hybridization of the bonding molecular orbitals of CO₂ with d orbitals of the Pt atoms. Our results show that, for adsorption on TiO₂-supported Pt octamers, the O–C–O bending and C–O asymmetric stretching frequencies can be used as reliable indicators of the presence of the CO₂^– anion intermediate as well as to distinguish unique adsorption geometries or sites. Finally, we suggest a possible pathway for subsequent CO₂ dissociation to CO at the surface of a reduced anatase TiO₂ (101)-supported Pt octamer, which has a computed energy barrier of 1.01 eV