Density Functional Theory (DFT) Study On The Adsorption Of CO₂ On Cu₂O (111) Surface

The formation of methanol via photocatalytic reduction of carbon dioxide with water is of very importance in the research of simulating photosynthesis due to severe environmental pollution and energy shortage. The main target is to design or find out efficient and stable photocatalysts. The photocatalysts for the reaction of formation of methanol via CO₂ photocatalytic reduction with H₂O must have at least the ability of transforming the solar energy into chemical energy and surface active sites for activating carbon dioxide and water molecules.Cu-based catalysts are commonly used in the industry of methanol synthesis. It was found that CO₂ is the direct carbon source for methanol instead of CO, and the reaction active site for methanol formation is Cu⁺ ions. It has been reported in 1998 that Cu₂O can split water molecules into H₂ and O₂ with the visible light irradiation. Thus, Cu₂O is one of the best photocatalysts for the target reaction.In this paper, we have studied the adsorption of CO₂ on the nonpolar surface of Cu₂O at the DFT/B3LYP level by using the embedded cluster model. The main results are listed as follows:1. The energy separation of our embedded cluster is 2.22 eV, which is consistent with the experimental results of 2.4±0.3 eV.2. We obtained three chemical adsorption states: vertical adsorption on unsaturated Cu, triangle adsorption on unsaturated O andη²-C, O coordinated on unsaturated O and Cu simultaneously.3. In the study of adsorption of CO₂ on Cu₂O (111) surface, the stable adsorption sites are unsaturated Cu and O. The adsorption energies of three chemical adsorption states are: 86.13, 165.33, and 224.86 kJ/mol respectively.4. The Mulliken population analysis indicates that unsaturated O and Cu are the most possible adsorption sites. The charges transfer from Cu₂O cluster to the CO₂ by -0.63 e and -0.58 e, respectively.