The Structure And Catalysis Of Ceria-Based Metal Nanoparticles By Density Functional Theory Study

CeO2is a kind of rare earth oxides, which with fluorite structure. It has a good release oxygen storage capacity due to reversible exchange between Ce4+and Ce3+, it is applied in many fields, such as automotive three way conversion, purification of volatile organic compounds and so on. However, the catalytic activity of the separate CeO2is weak. When metal nanoparticles load to the CeO2, the catalysis is significantly improved. It is difficult to explain the influence and electronic mechanism between metal nanoparticles and CeO2, experimentally. In this paper, we use the density functional theory and build a reasonable computational model. A systematic study of the influence and electronic properties between nano metal particles and CeO2is applied in the article. This may provide a theoretical basis for the development of efficient low-temperature catalyst.We use the density functional theory to study the adsorption behavior and oxidation activity of the oxygen, which adsorb on the gold carrier or CeO2supported gold. Compared with the adsorption behavior of oxygen adsorb on different surfaces, such as Au(111)+Platform surface,3Au/Au(111)+stepped surface, Aui9+clusters and CeO2supported on positive Au9clusters. From the electronic properties, this article has a good explanation of why the O2in separate positive gold carrier exhibit weak interaction, and when the positively charged gold clusters supported on CeO2surface, it has a strong interaction with O2. CeO2substrate can be seen as an electronic container, it can get and store electrons from the gold clusters, when gold clusters interact with O2and it will release electrons. In this work, it is the first time to confirm possible oxygen species in different locations based on the gold catalyst. The picture of spin differential density shows that O2becomes the peroxide when O2adsorb the hole of Au9clusters. However when O2adsorb on Ce top position which locate at the boundary, corner or far from the Au9clusters, the formation of oxygen species are all superoxide. We also find an interesting phenomenon that Ce3+distribution on Aun/CeO2catalysts are diverse, and with different external conditions change. Using CO as a probe molecule, we compare the catalytic activity of superoxide and peroxide which locate at the different positions of the Au9/CeO2catalyst. Our calculations show that the superoxide which near the Au9clusters has the best reactivity. That is to say, the active site of Aun/Ce02catalyst is at the Interface of gold clusters and CeO2.The article also has systematically studied the structures of gold nanoparticles which adsorb on different surface of CeO2. Gold clusters have been adsorbed on CeO2(110) and (100) surfaces, respectively. And when on the CeO2(110), the result shows that a single Au atom prefer to adsorb on the oxygen or hollow site. And if the number of gold atoms is2-10, the structure of gold clusters is prefer to be two-dimensional structure. When the number of gold atoms is increased, the most stable adsorption structure on the CeO2(110) is no longer in2D, but a3D structure. On the CeO2(100) surface, for Aux(x=1-4), they prone to be single-atom dispersion. However, the number of Au atoms has been increased, such as6or8atoms, tend to be in3D structure. When the Aux clusters are adsorbed on the different O-O bridge positions, the adsorption energies may be different.Finally, we systematically calculated an inverse CeO2/Ag catalyst and the adsorption of oxygen on it. A single oxygen atom prefers to adsorb at the fcc or hcp hollow site of Ag (111) surface. When adsorbing on the cerium top site, it is very weak. When the CeO2adsorb on Ag (111) surface, the adsorption structures tend to gather together. When O2adsorbs on CeO2/Ag (111) surface, the most stable site is the interface, and when the O2away from CeO2, the adsorption structure is unstable. The work also finds that when O2adsorb at the top site of cerium or hollow position, the oxygen species is superoxide, as well as the far away from the CeO2. When O2adsorb on the interface of CeO2/Ag (111), it is also superoxide.