| The high pressure of environmental regulations around the world has intensified the need for high efficient catalysts. CeO2, as an ideal candidate of noble metals, has aroused wide concern among people. Because of limited catalytic performance of single component, it is imperative to develop new CeO2-base catalytic materials for different industries. Modified CeO2 with other metal elements were proved to be an effective way to improve the catalysis performance. What’s more, traditional experiments and detection methods could not clearly and directly show explanations about the process and mechanism of whole catalytic reactions. Thus, it is necessary to give a molecular-level understanding of the underlying mechanism governing the catalytic performance by using calculation methods. In this study, we focus on the application of CeO2 on three way catalysis reactions for automotive emission. The catalytic performance of Sm supported and doped in CeO2(111) and the interaction of the CO molecule with Sm0.08Ceo.9202(111) surface were presented by using spin-polarized DFT+U calculations in many ways. The main works are summarized as follows:Firstly, the stoichiometric CeO2(111) was investigated. We calculated and analyzed the oxygen vacancy formation, geometry structure and electronic properties and also made a comparison with others. The similarity results were obtained and proved the validity of our computed methods and models, which would lay a good foundation for the following computation parts of Sm supported and doped CeO2(111) surface.Secondly, we studied the Sm supported CeO2(111) surface. The supported Sm atom have an adverse influence on the catalytic performance of CeO2(111). The oxygen vacancy formation energies at different sites on Sm supported CeO2(111) surface are much larger than that on the stoichiometric CeO2(111) surface.Thirdly, Sm doped CeO2(111) surface was investigated and the structures and electronic properties of the doped surface were compared with undoped CeO2 surface. Oxygen vacancy formation energies of various sites were calculated and found the oxygen vacancy formation energies were reduced by more than 50% after Sm doping compared to the undoped system. To explore the main factors influencing the oxygen vacancy formation energy, we analyzed the change of the relaxed geometric and electronic structures by Sm doping. Large structural distortion which result in a relatively weak interaction of the lattice oxygen with the Sm-doped CeO2(111) surface and the changes of O-2p state of neighboring oxygen atoms around doped Sm atom were responsible for the reduced oxygen vacancy formation energies.Finally, the interaction between CO molecules and the Sm0.08Ceo.92O2(1 11) was investigated by placing a CO molecule at many different sites on the relaxed Sm0.08Ce0.92O2(111) surface. Unlike a stoichiometric CeO2(111) surface observed with only the presence of physisorbed CO, the Sm dopant promotes the direct oxidation of CO by taking away an oxygen atom from the stoichiometric CeO2(111) surface, thus leading to the formation of a CO2 molecule and an oxygen vacancy leaving on the surface, expecially on O-top sites. For performing further comparison and analysis of catalytic oxidation mechanism for CO oxidation, the Bader charge, the charge density difference and partial density of states are numerically simulated. |
PDF Full Text Request