O₂ activation by subnanometer Re-Pt clusters supported on TiO₂(110): exploring adsorption sites

Activation of O₂ by subnanometer metal clusters is a fundamental step in the reactivity and oxidation processes of single-cluster catalysts. In this work, we examine the adsorption and dissociation of O₂ on RePt (n + m = 5) clusters supported on rutile TiO₂(110) using DFT calculations. The adhesion energies of RePt clusters on the support are high, indicating significant stability of the supported clusters. Furthermore, the bimetallic Re-Pt clusters attach to the surface through the Re atoms. The oxygen molecule was adsorbed on three sites of the supported systems: the metal cluster, the surface, and the interface. At the metal cluster site, the O₂ molecule binds strongly to RePt clusters, especially on the Re-rich clusters. O₂ activation occurs by charge transfer from the metal atoms to the molecule. The dissociation of O₂ on the RePt clusters is an exothermic process with low barriers. As a result, sub-nanometer Re-Pt clusters can be susceptible to oxidation. Similar results are obtained at the metal-support interface, where both the surface and cluster transfer charge to O₂. To surface sites, molecular oxygen is adsorbed onto the Ti₅ atoms with moderate adsorption energies. The polarons, which are produced by the interaction between the metal cluster and the surface, participate in the activation of the molecule. However, dissociating O₂ in these sites is challenging due to the endothermic nature of the process and the high energy barriers involved. Our findings provide novel insights into the reactivity of supported clusters, specifically regarding the O₂ activation by Re-Pt clusters on rutile TiO₂(110).