Metal−Oxide Interfacial Reactions:  Encapsulation of Pd on TiO₂(110)

Abstract

The model system Pd/TiO2 (110) was used to evaluate the correlation between metal encapsulation and electronic structure of TiO2 crystals. We observed encapsulation of Pd clusters supported on TiO2 crystals, which were heavily Ar+ sputtered, Nb-doped, or reduced by vacuum annealing. In contrast, encapsulation was not observed on unreduced, undoped, or slightly sputtered TiO2 crystals. Our results indicate a strong dependence of the encapsulation process on the electron density in the conduction band of TiO2 and on the space charge formed at Pd/TiO2 interfaces. This behavior is controlled by the initial position of the Fermi energy level (EF) of the metal and the oxide before contact is established. We proved that encapsulation reactions are favored by n-type doping of the oxide and a large work function of the metal. On the basis of this mechanism, we conclude on general trends controlling encapsulation reactions of oxide-supported metal clusters and the strong metal-support interaction (SMSI).

Preparation of Novel Complex Nano-Structured Gold Catalyst Au@T<sub>i</sub>O<sub>2</sub>/MCM-22, Characterization and Remarkably Catalytic Performance for Cyclohexane Oxidation

“…It is reported that the metals with high surface energy such as Pt and Pd are more likely to be encapsulated than those with low surface energy (e.g. Au and Cu) [18].…”

Developing a High Density Pt/Alumina Hermetic Feedthrough

“…On the other hand, Zhong et al [15] shown that almost entire platinum surface is covered with ceramic. In addition to that, the side view secondary electron image shown in figure 8-16 also showed that altering the particle size altered the microstructure of the ceramic coating As discussed in section 2.3.2, because of difference in the surface tension and work function of metal and oxide, TiO 2 could migrate on the surface of the platinum particle and encapsulated it; while in normal condition it is not possible for aluminum oxide to cover the platinum [26]. However, in a reduced atmosphere at high temperatures, alumina migrates over the surface of the platinum and covers it.…”

“…In nanostructured metal/oxides system, the contribution from the surface and the interface energies to the total free energy could be significant and should be considered in the thermodynamic calculation. Several studies [26,77,78] showed that minimization of the surface energy of a system is one of the main driving forces for an encapsulation reaction, as shown in figure 2-9 b. In this case metals with high surface energy (e.g., Pt and Pd, but not Au, Cu) favor encapsulation and oxides with low surface energy such as TiO 2 and V 2 O 5 , more easily undergo the encapsulation state than oxides with relatively high surface energies, such as SiO 2 and Al 2 O 3 [26,78].…”

“…Metal films on oxide ceramics have been widely studied in the process of heterogeneous catalysis [8,[21][22][23][24][25][26]. The reactivity and stability of such a catalyst depends strongly on the interaction of metal and ceramic.…”

“…The reactivity and stability of such a catalyst depends strongly on the interaction of metal and ceramic. [26,36,46].…”