CO₂ Activation on Cu/TiO₂ Nanostructures: Importance of Dual Binding Site

CO₂ adsorption and activation on Cu single atom catalysts and Cu nanoclusters supported on the (110) surface of rutile and on the (101) surface of anatase TiO₂ have been investigated by means of first principles electronic structure calculations. The role of oxide reduction associated to the presence of oxygen vacancies has been considered. Five main messages emerge from this study. (1) CO₂ activation on Cu/TiO₂ nanostructures is surface sensitive, as the rutile and anatase surfaces can exhibit different behaviors; (2) the surface morphology is essential since CO₂ is activated only when the molecule can simultaneously bind to at least two active sites, such as a Cu atom on one side and an oxide ion on the other site; (3) Cu atoms on TiO₂ are in the +I oxidation state and can bind and activate CO₂ via charge transfer from the oxide; (4) on supported Cu clusters CO₂ activation occurs mostly at the metal/oxide interface; (5) the presence of O vacancy sites facilitates the spontaneous dissociation of CO₂ to CO, or increases the electron density of the metal catalyst, two effects that can influence the mechanism of CO₂ reduction to methanol or other chemicals.