<i>Ab Initio</i> Investigation of CO₂ Adsorption on 13-Atom 4d Clusters

Abstract

In this work, we report an <i>ab initio</i> investigation based on density functional theory calculations within van der Waals D3 corrections to investigate the adsorption properties and activation of CO₂ on transition-metal (TM) 13-atom clusters (TM = Ru, Rh, Pd, Ag), which is a key step for the development of subnano catalysts for the conversion of CO₂ to high-value products. From our analyses, which include calculations of several properties and the Spearman correlation analysis, we found that CO₂ adopts two distinct structures on the selected TM₁₃ clusters, namely, a bent CO₂ configuration in which the OCO angle is about 125 to 150° (chemisorption), which is the lowest energy CO₂/TM₁₃ configuration for TM = Ru, Rh, Pd. As in the gas phase, the linear CO₂ structure yields the lowest energy for CO₂/Ag₁₃ and several higher energy configurations for TM = Ru, Rh, Pd. The bent CO₂ (activated) is driven by a chemisorption CO₂-TM₁₃ interaction due to the charge transfer from the TM₁₃ clusters toward CO₂, while a weak physisorption interaction is obtained for the linear CO₂ on the TM₁₃ clusters. Thus, the CO₂ activation occurs only in the first case and it is driven by charge transfer from the TM₁₃ clusters to the CO₂ molecule (i.e., CO₂^-δ), which is confirmed by our Bader charge analysis and vibrational frequencies.