First-principles Calculation On The Synergistic Effect Of Pt And Grain Boundary Of CeO₂ Surface In CO Oxidation

Ceria is a widely used semiconductor material,which is generally used as catalyst or catalyst support for various reactions.The unique electron local properties of Ceatom 4f orbital lead to the excellent oxygen storage and release capacity of ceria,hence more and more ceria catalysts are widely used.Currently,metal atoms supported on the surface of cerium dioxide are the most common cerium oxide catalyst form.Which not only solves the problem of catalyst sintering,but also improves the catalytic activity of the catalyst.In addition to surface,grain boundary（GB）is also a very important surface defect,which has important applications in the field of catalysis.In fact,GBs are generally exposed on the surface,and it is difficult to fully reflect the surface characteristics of real materials with conventional theoretical models.Therefore,little attention has been paid to the effect of GBs on surface catalytic properties.In this study,we built a new type of cerium dioxide catalyst system,mainly selected CeO₂Σ3（111）GB model exposed on CeO₂{110}surface as the catalyst carrier,and explored the segregation and adsorption properties of Pt atoms on the carrier,to study the influence of GB on the segregation and adsorption of Pt atoms,and verified the catalytic activity of the GB model based on the CO oxidation process.In this paper,we performed our DFT calculations using Quick Step module in CP2K software package.A series of sites for Pt segregation was selected on two different CeO₂Σ3（111）GB surface,and to explore the segregation and aggregation tendency of Pt.Finally,we resorted to the CO catalytic oxidation on the three system of Pt&CeO₂GB@surface to obtain the reaction mechanism and the reaction barrier of CO oxidation.The main conclusions of these two works are as follows:（1）The segregation sites of Pt were selected in the（110）and（112）GB models respectively,and the segregation trends of Pt on different GB surfaces were obtained.In modelⅠ,the trend of Pt segregation was GB@surf.>GB@Bulk>Surf.>Bulk.In modelⅡ,the trend of Pt segregation was GB@surf.>Surf.>GB@Bulk>Bulk.Considering the aggregation of Pt atoms,we found that there was an obvious repulsive interaction between the two Pt atoms when further introducing Pt atoms to the pure GB surface.Therefore,Pt atoms are not conducive to aggregation on the GB surface.（2）In the presence of oxygen vacancy,Pt has a greater tendency to the（110）surface than the（112）surface,and the divergence energy is 0.28 e V.When Pt atoms are added to the pure oxygen vacancy@GB@surface,the two Pt atoms have a weak repulsive interaction.Hence,in the case of oxygen vacancy,Pt atoms are still not conducive to aggregation on the GB surface.（3）Pt atom reduces the formation energy of oxygen vacancy,and oxygen vacancy can be generated spontaneously in the presence of Pt segregation,which laid a good foundation for the subsequent CO oxidation on the GB surface.（4）When Pt adsorbs on the GB surface,we use the total energy to determine the optimal adsorption location for Pt.Compared with the pure surface model,it was found that the GBs promoted the adsorption of Pt on the GB surface.（5）The CO oxidation on Pt segregation system,pure GB system and Pt adsorption system was studied,and the following conclusions were obtained:（i）On the Pt@CeO₂GB surface,CO oxidation follows the Mv K mechanism and only overcomes the barrier of 0.249 e V.（ii）On the pure GB surface,CO oxidation follows L-H mechanism and needs to overcome the barrier of 0.405 and 0.405 e V.（iii）On the Pt/CeO₂GB surface,we tested two oxidation processes,the oxidation process following the Mv K mechanism needs to overcome barries of 1.007 and 0.148e V,while the recation along the L-H mechanism needs to overcome barries of 0.228and 0.715 e V.No matter which reaction path it is,the barrier energy is larger than the others,indicating that compared with the other two systems,the catalytic oxidation of CO in this system is more difficult,and CO₂molecules are not easy to dissociate ultimately and are more inclined to adsorb on Pt atoms.In this paper,the interaction between Pt and CeO₂GB surface and the interaction between Pt and oxygen vacancy have been systematically investigated using first-principles calculations based on density functional theory.We also investigated the catalytic oxidation process of CO in different Pt&Ce_1-xO₂systems.We studied for the first time the properties of compound catalyst containing GB surface based on CeO₂,and the GB model was applied to the catalytic oxidation of CO,which provided a new idea for the design of new catalysts.