A Density Functional Theory Studies Of The Doped And Inversed Ceria-Based Catalysts

Ceria has a brilliant oxygen storage capacity and catalytic performance due to the reversible conversion between Ce⁴⁺and Ce³⁺ions,has been widely used in the fields of heterogeneous catalysis and gas sensors.However,the pure ceria surpport has relatively low catalytic activity and poor thermostability,which is inclined to be deactivated under high temperature.How to enhance the catalytic activity and thermostability of CeO₂ support is one of the hotspots of catalysis science.On the other hand,deeper understanding of the active sites,active species and reaction mechanism of ceria-based catalysts is of great significance for the design and development of the catalysts that of high activity under low temperature.In this work,the metal ion doped catalysts and inverse CeO₂ catalysts models were constructed;the structure and properties of doped catalysts,the structure and catalytic performance of inverse catalysts were systematically studied by density functional theory?DFT?and artificial intelligence technology.Experimental results suggest that Ti doping into CeO₂ is one of the crucial methods to modify CeO₂ support because the doping could improve the support's catalytic performance and thermostability.The disproportion and distribution of Ti ion in CeO₂ greatly affect the support's phase and catalytic performance.Limited by the synthesizing methods of catalysts,Ce_1-xTi_x O₂ solid solution of various structures are experimentally difficult to prepare.Thus,it is of great significance to study the distribution of doped Ti ions at molecular level on the structure of solid solutions by theoretical methods.In this work,using SOD?site-occupancy disorder?program,cubic phase,anatase phase and rutile phase Ce_1-xTi_xO₂ model oxides with different Ce/Ti ratios?14/2,12/4,10/6,8/8,6/10,4/12 and 2/14?were generated by designing Ce_1-xTi_xO₂ solid solutions with different Ti ion doping ratios.The first-principles-based VASP?Vienna Ab-inito Simulation Package?package was employed to optimize the structure of all the configurations.The calculation results indicate that 1.Ce,Ti ions distributed evenly in Ce_1-xTi_xO₂ solid solution;2.The crystal phase of Ce_1-xTi_xO₂ solid solution changes along with the Ce/Ti ratios.When Ce/Ti ratio is low,Ce_1-xTi_xO₂ exists in anatase phase;as the Ce/Ti ratio increases,the anatase phase transforms into monoclinic phase;as the Ce/Ti?3/1,Ce_1-x-x Ti_xO₂ exists in the most stable cubic phase.On the basis of systematically studied the structure of Ce_1-xTi_xO₂ solid solution and obtaining the most stable configurations of the corresponding Ce/Ti model catalysts,four model materials,Ce₁₆O₃₂,Ce₁₄Ti₂O₃₂,Ce₈Ti₈O₃₂2 and Ce₂Ti₁₄O₃₂,were selected and studied the electronic and optical properties by density functional theory.The calculation results suggest that 1.By analyzing the electronic properties of band structure and density of states,the band gap of Ce_xTi_1-xO₂ solid solution was found to decrease with the increase of Ti content and the conduction band decreases consequently,which is of great significance to the development of photo catalysts.2.By population analysis,it is found that the Ti doping increases the population between Ce-O and O-O,and consequently shortens the distance between corresponding atoms.Therefore,Ti doping can increase the interaction between Ce and O.3.Optical analysis indicates that Ti doping makes the absorption curve of ultraviolet move towards low wave number,which improves the ultraviolet absorption of cerium oxide and partly enhances the optical properties of cerium oxide.Ceria supported on metal films catalysts?CeO₂/M?can supply crucial information for analyzing the active centers and reaction mechanism of metal nanoparticle supported ceria catalyst?M_x/CeO₂?.However,restricted by the current experimental skills,it's hard to obtain the micro-electronic structure and catalytic mechanism of CeO_2-x-x interacting with metals at the molecular level.Therefore,it is of great significance to systematically study the geometry,electronic structure and catalytic mechanism of CeO_2-x-x supported metal films at atomic level by theoretical methods.In this work,VASP program package based on density functional theory and global structure search program?LASP?were employed to systematically study the structure of Ce_nO_2n/Rh?111?and Ce_nO_2n-x/M?111??M=Cu?Au?Rh?.The calculation results substantiate that 1.Compared with chainlike structure,cerium oxide is more stable in cluster structure on Rh?111?;2.Compared with hexagonal and trigonal Ce_nO_2n-2n-2 clusters on Rh?111?,trigonal cluster is found to be more stable;3.On the surface of Rh?111?support,Ce_nO_2nn cluster is more stable than nonstoichiometric Ce_nO_2n-xn-x cluster;4.Compared the structures of Ce_nO_2n-xn-x clusters at different metal substrates,the stability of inverse catalysts are as below:Ce_nO_2n-x/Rh?111?,Ce_nO_2n-x/Cu?111?,Ce_nO_2n-x/Au?111?.Theoretical analysis found that this is resulted from the lattice size matching and electron interaction between cerium oxides clusters and substrates.Based on the systematic study of Ce_nO_2n/Rh?111?structures,I investigated the adsorption and reaction behaviors of CO and O₂ on Ce₇O₁₄/Rh?111?and Ce₇O₁₂/Rh?111?by density functional theory method.The calculation results show that:1.The adsorption of CO and O₂ on CeO₂ is the weakest,while that at the interface is the strongest.When O₂ adsorbs on CeO₂,it gains an electron and becomes a superoxide species;while adsorbs at the interface,it gains two electrons to be a peroxide species.The more electronic interacts between O₂ at interface explains the strongest adsorption of oxygen at the interface.2.For high-coordinated oxygen species,the E-R mechanism is favorable,and for low-coordinated oxygen species,both L-H and E-R mechanisms are easy to occur;3.The difficulty of CO reaction is related to the coordination number of oxygen species.The lower coordination number of oxygen species is,the easier the reaction of CO oxidation occurs.4.Compared with the partially reduced CeO₂,the stoichiometric CeO₂ has lower barrier of CO oxidation reaction.