Study On The Structure-activity Relationship Of Oxide Solid Solution:Explore The Relationship Between The Valence State Of Solute Cations,Vacancy Concentration And Reaction Performance

Metal oxide solid solutions generally possess better physical and chemical properties than single oxides.The doping of secondary cations to form a solid solution structure can effectively improve structural and thermal stability of a material,which is also a strategy to rationally design active sites of a metal oxide catalyst.Therefore,an in-depth study on structure-activity relationship of oxide solid solutions helps the rational design and precise control of catalysts.In this dissertation,different valent metal cations were doped in the lattices of the p-type semiconductor NiO and the n-type semiconductor CeO₂ catalysts to form solid solutions,and the doping effect on the number of active sites and the relationship between active sites and the reactivity for CO catalytic oxidation reaction were elucidated.The main findings are as follows.1.To explore the effect of doping cation valence on the amount of Ni³⁺in NiO and the activity for CO oxidation,Li⁺,Zn²⁺and Cr³⁺cations were selected as NiO dopants to synthesize pure phase solid solution catalysts Ni_0.9M_0.1O.The results of XRD,HRTEM,Raman,UV-vis and DFT show that three different valent cations replace the Ni²⁺cations in the NiO lattice to form a solid solution.TPR,Raman and XPS results demonstrate that doped Li⁺is conducive to the production of lattice and surface Ni³⁺,while doped Zn²⁺and Cr³⁺reduces lattice and surface Ni³⁺cations content.The intrinsic activity of CO follows the order of Ni_0.9Li_0.1O>NiO>Ni_0.9Zn_0.1O>Ni_0.9Cr_0.1O,indicating that the CO oxidation reaction activity on NiO solid solution is determined by the number of Ni³⁺cations.Therefore,the catalytic oxidation performance of the NiO-based catalyst can be tailored by adjusting the Ni³⁺cations content via the doping of cations with different valence cations.2.To study the effect of doping cation valence on the oxygen vacancy in CeO₂and the activity for CO oxidation,Li⁺,Zn²⁺,Y³⁺,Zr⁴⁺and Nb⁵⁺metal cations with different valences were selected as dopants to form a pure solid solution catalyst Ce0.9M0.1O2-δ.The results of XRD,HRTEM,Raman and UV-vis were used to prove the formation of the solid solution structure in the samples Ce_0.9M_0.1O_2-δ.The results of Raman,O₂-TPD and XPS prove that Li⁺,Zn²⁺,Y³⁺and Zr⁴⁺cations doping in CeO₂lattice promotes the formation of more oxygen vacancies,while Nb⁵⁺doping reduces the content of oxygen vacancies.The intrinsic activity of CO oxidation follows the order of Ce0.9Li0.1O2-δ>Ce0.9Zn0.1O2-δ>Ce0.9Y0.1O2-δ>Ce0.9Zr0.1O2-δ>CeO2>Ce_0.9Nb_0.1O_2-δ.Therefore,by doping with low-valent cations to form a solid solution,a catalyst with higher activity for CO oxidation can be obtained.3.For NiO and CeO₂ systems doped with different cations,it is found that the apparent activation energy of CO oxidation reaction is linearly correlated to the band gap of the catalyst.The smaller the band gap,the smaller the activation energy for CO oxidation reaction.Therefore,the nature of the doping of cations with different valences into both n-type and p-type semiconductor oxides can be attributed to the regulation of the band gap,thereby regulating the catalytic oxidation reactivity.The findings in this dissertation can provide a new idea for the rational design of semiconductor oxide catalysts.