Study Of Electronic Structure And Oxygen Storage/Release Mechanism On Transition Metal Doped Ceria-based Materials

Recently, for the drastic increase of the automotive, the huge quantity of exhausts makes the atmosphere environment worse than before. According to the strict regular, there are many challenges for the clarify catalysts. Transition metal has an impressed effect on the development of the oxygen storage capacity and catalysis activity. Unfortunately, there is no clear mechanism for such system. The ab initio density function theory has been employed to study the electronic structure and oxygen storage mechanism on the transition metal doped ceria-based materials.Based on the combination of density function theory and Hubbard U model, an unlinear core corrected ultra soft pseudopotential has been used. During the oxygen release process, there are two extra electrons left by the removing of the neutral oxygen, which has been totally localized on the nearest neighborhood of the oxygen vacancy. According to the strong correlation effect, the Ce 4f band has been spited by the electron occupation. On the other hand, oxygen storage is the reverse process of release. During the oscillation of the oxygen partial pressure, the formation and accommodation of oxygen vacancy result in the occupation and unoccupation of Ce 4f bands.For FeO and NiO, the modified DFT+U methods have been employed to study the spin split mechanism of 3d electrons. Through changing the initial occupation state of 3d and the symmetry distortion of local structures, the t2g state of Fe 3d have been totally splited, which predicts that FeO is insulator.For Fe, Ni doped ceria-based materials, Hubbard U model has been used to deal with Fe 3d, Ni 3d and Ce 4f. For iron dopant, there is a strong Fe 3d-Ce 4f interaction due to the combination of Fe 3d and Ce 4f in the conduct band, which lower the oxygen formation energy and promote the oxygen release process. On the other hand, Ni dopant induced a gap state between the O 2p and Ce 4f, which means that Ni will be reduced through the oxygen release process instead of Ce. Although there are different dopants effect in details, generally a lower energy level than the empty Ce4f band to accommodate the extra electron would be the basic mechanism for the increased redox ability.