CO₂ adsorption on gas-phase Cu_4−xPt_x (x = 0–4) clusters: a DFT study

Transition and noble metal clusters have proven to be critical novel materials, potentially offering major advantages over conventional catalysts in a range of value-added catalytic processess such as carbon dioxide transformation to methanol. In this work, a systematic computational study of CO₂ adsorption on gas-phase Cu_4−xPt_x (x = 0–4) clusters is performed. An exhaustive potential energy surface exploration is initially performed using our recent density functional theory basin-hopping global optimization implementation. Ground-state and low-lying energy isomers are identified for Cu_4−xPt_x clusters. Secondly, a CO₂ molecule adsorption process is analyzed on the ground-state Cu_4−xPt_x configurations, as a function of cluster composition. Our results show that the gas-phase linear CO₂ molecule is deformed upon adsorption, with its bend angle varying from about 132° to 139°. Cu_4−xPt_x cluster geometries remain unchanged after CO₂ adsorption, with the exception of Cu₃Pt₁ and Pt₄ clusters. For these particular cases, a structural conversion between the ground-state geometry and the corresponding first isomer configurations is found to be assisted by the CO₂ adsorption. For all clusters, the energy barriers between the ground-state and first isomer structures are explored. Our calculated CO₂ adsorption energies are found to be larger for Pt-rich clusters, exhibiting a volcano-type plot. The overall effect of a hybrid functional including dispersion forces is also discussed.