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 TiO(2-)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.