Theoretical Study On The Effect Of Transition Metal Oxide Surface On The Photocatalytic Decomposition Of N₂O

N₂O is one of the nitrogen oxides compounds（NO_x）emitted by industrial exhaust gas and motor vehicle exhaust gas,which can produce a great greenhouse effect.Therefore,it is very important to design and develop a catalyst that can efficiently photocatalyst the N₂O decomposition.The study of the reaction mechanism and the nature of catalysis on the atomic scale can provide important scientific and theoretical guidance for the development of new and efficient photocatalysts.In this thesis,the photocatalytic decomposition reaction of N₂O on a series of transition metal oxide catalysts of CeO₂,TiO₂ and Bi VO₄ was studied by density functional theory.A series of different CeO₂,TiO₂ and Bi VO₄ models were constructed respectively.Including the stoichiometric and defective surface of CeO₂（110）,（111）and2x1 reconstructed（110）,TiO₂（101）and（001）and Bi VO₄ orthorhombic（002）and monoclinic（011）.The effect of the different morphologies of the catalyst is explained on the atomic scale,and the influence of the surface morphology of the catalyst on the light absorption properties,electron transfer and the mechanism of N₂O photocatalytic decomposition is deeply discussed.The main work of the research is summarized as follows:（1）The photocatalytic decomposition of N₂O is studied on two surfaces of CeO₂（110）and（111）.The difference in the absorption of ultraviolet-visible light between the two surfaces can be ignored.The excited electron tends to be localized on the surface,but it will be affected by the Ce³⁺near oxygen vacancy.The energy barrier for the migration of excited electrons on the（110）surface is slightly lower than that on the（111）surface,indicating that the（110）surface shows a higher electron migration rate.For the photocatalytic decomposition mechanism of N₂O,we found that it is difficult to decompose the N₂O on the perfect CeO₂ due to the high reaction energy.But the reaction energy will be significantly reduced if the system with excited electrons or excess electrons,which is related to the state of dissociated O.（2）The photocatalytic properties of reduced CeO_2-x（110）surface and the whole dissociation process of N₂O into N₂ on this surface with different O vacancy positions are investigated.It can be found that the position of O vacancy has a negligible effect on light absorption due to the similar band gap value of CeO_2-x itself.However,the different O vacancy position affects the localization and migration of excess electron or excited electron.The electron may localize on the bulk site and cannot transfer to the surface to participate in the reaction,which has an impact on photocatalytic performance.For the photochemical reaction,the O vacancy at different positions affects the reaction by changing the coordination of the adjacent Ce.（3）As a common phenomenon on the surface of CeO₂（110）,the 2x1 reconstructed CeO₂ surface is used to study the photocatalytic properties and performance of CeO₂（110）-2x1 reconstructed surface by photocatalytic decomposition of N₂O on its surface.The reconstructed surface exhibits stronger light absorption ability compared to the unreconstructed surface in the near-ultraviolet and visible light regions,which indicates more photo-generated carriers would generate.In the CeO₂ photocatalytic decomposition reaction of N₂O,CeO₂（110）-2x1 reconstruction surface not only exhibits the feature of the CeO₂（110）-1x1 surface,but also shows feature properties of CeO₂（111）surface.Considering that the reconstruction surface exhibits better light absorption performance under similar photochemical reaction performance.Thus,the conclusion that it has a stronger photocatalytic ability can be drawn.（4）The photocatalytic decomposition of N₂O on the anatase（101）and（001）surfaces have been studied.In the study of the absorption spectrum,it is found that the（001）surface exhibits better absorption performance,while the excited electron migration is less affected by different surfaces.In the reaction,N₂O is difficult to decompose on the perfect surfaces without the excited electrons.Like the reaction on the CeO₂ system,the reaction energy will be significantly reduced if the system with excited electrons or excess electrons,which is related to the state of dissociated O.（5）Several different BiVO₄ photocatalysts were designed and synthesized by the hydrothermal method.Through their photocatalytic activity test,it was found that the monoclinic Bi VO₄ with the most O vacancies exhibited the best performance in the absorption of visible light,the separation efficiency of photogenerated carriers,and the photocatalytic decomposition of N₂O.Combined with the DFT calculation,the effect of O vacancies on the photocatalytic decomposition of N₂O is explained in detail.The excess electrons generated with O vacancies can significantly reduce the activation energy barrier.