Study On The Catalytic Mechanism Of CO Oxidation Reaction With Ceria-based Catalysts

CO emissions from chemical plant exhausts and automobile exhausts seriously affect environmental quality and human health.And the use of catalytic technology is currently a key way to purify CO.Non noble metal catalysts with cerium oxide as a carrier have shown wide application prospects in CO oxidation reactions due to their low cost and good catalytic performance.An in-depth understanding of the relationship between catalyst structure and performance at the atomic scale can provide important theoretical guidance for the design of novel and efficient catalysts.In this thesis,theoretical studies on the oxygen vacancy distribution,metal cluster size effect,crystalline surface effect and metal-carrier interaction on the surface of cerium dioxide were carried out to investigate the conformational relationship between active sites and catalytic performance,which is promising for the design of new high-performance CeO2-based catalysts in the catalytic oxidation of CO reaction by CeO2-based Cu catalysts.Here,we determined the oxygen vacancy distribution in 5 nm CeO2 nano-cubic particles based on the atomic pair distribution function(PDF)of total neutron scattering,combined with Reverse Monte Carlo(RMC)simulations.We found that 73.32%of the oxygen vacancies are distributed on the surface of CeO2 nanoparticles,19.29%on the subsurface,and the remaining 7.39%are diffused in the interior of the nanoparticles.Based on the density functional theory,the formation energy of oxygen vacancies on the surface is lower than that of vacancies on the subsurface,and the Madelung potential energy is positively correlated with the vacancy formation energy.And the 4f electrons are analyzed to have multi-group distribution,and the most stable electron groups are varied for different oxygen vacancies.By analyzing the geometry and electronic structure,it is obtained that the lattice distortion of the structure and the repulsion of 4f orbitals jointly affect the distribution of oxygen vacancies and the localization of Ce3+.The loading behavior of single-atom copper catalysts on the CeO2(100),(110)and(111)surfaces was investigated by DFT+U calculations.And we analyzed the effect of crystalline surface effects in Cu1/CeO2 catalysts on the catalytic activity of CO oxidation The CeO2(100)and(111)surfaces stabilize the active Cu+ species,while the Cu atoms arc present on the(110)surface in the form of Cu2+.The Cu+ was shown to be the active site for CO adsorption.which promotes the formation of reaction intermediates and lowers the reaction energy barrier.For the CeO2(100)surface,the interaction between CO and Cu is weaker and the CO adsorbed species are more likely to activate the lattice oxygen at the interface.The catalytic performance is closely related to the binding strength of CO and Cu single atoms.The diffusivity of Cu atoms on different crystallographic surfaces of CeO2 was calculated using density functional theory.It was obtained that on the CeO2(111)surface,Cu atoms tend to aggregate into large clusters;on the CeO2(110)surface,Cu atoms tend to exist in smaller-sized clusters;and on the(100)surface,Cu atoms exist as highly dispersed single atoms.The catalytic activity of CeO2(111)loaded Cu8 cluster catalysts for CO oxidation was investigated.The excellent performance of Cu/CeO2 catalysts is related to the interfacial interaction between Cu and CeO2 and their synergistic redox behavior,and the interaction of oxygen vacancies with Cu clusters promotes the generation and stabilization of active Cu+ species.These results provide important insights for the rational design of ceria and other reducible oxide loaded catalysts.