Abstract
Noble metal particles supported on transition metal oxides (TMO) may undergo a so-called strong metal–support interaction via encapsulation. This perspective addresses catalytic properties of the metal catalysts in the SMSI state which can be explained on the basis of complementary studies performed on well-defined, metal-supported TMO films. In particular, the results of low temperature CO oxidation revealed the key role of weakly bound oxygen species provided by a two-dimensional (“monolayer”) oxide film. The binding energy of such oxygen atoms can be used as a descriptor for oxidation activity. Reaction rate enhancement often observed for TMO films partially covering the metal surface is rationalized within a mechanism in which the metal acts as a promoter to create the most active “oxidered/oxideox” interface formed by reduced and oxidized phases in the film. Although only low temperature CO oxidation is considered, it is tempting to generalize these ideas to other oxidation reactions following the Mars–van Krevelen type mechanism. In addition, metal-supported ultrathin TMO films may serve as well-defined model systems to examine different aspects of the “electron theory of catalysis” which was proposed long ago and which is based on electron transfer mechanisms.Graphical
Highlights
The term strong metal–support interaction (SMSI) is commonly associated with the original works of Tauster and coworkers from the late 1970s, who observed that the uptake of H2 and CO drops after some treatment of oxide-supported noble metal catalysts, most markedly for Pt supported on TiO2 [1, 2]
One may reasonably assume that the catalytic properties of transition metal oxides (TMO) supported metal catalysts in the SMSI state is intimately linked with the structure and reactivity of metal-supported ultrathin TMO films
CO uptake measured by temperature programmed desorption (TPD) drops to almost zero upon hightemperature annealing, and as such the system manifests the classic SMSI effect
Summary
The term strong metal–support interaction (SMSI) is commonly associated with the original works of Tauster and coworkers from the late 1970s, who observed that the uptake of H2 and CO drops after some treatment of oxide-supported noble metal catalysts, most markedly for Pt supported on TiO2 [1, 2]. One may reasonably assume that the catalytic properties of TMO supported metal catalysts in the SMSI state (via encapsulation) is intimately linked with the structure and reactivity of metal-supported ultrathin TMO films. This is the focus of the present Perspective. Well-ordered oxide films grown on metal single crystal surfaces have long been used as planar model systems for studying chemical reactions at oxide surfaces and of metal nanoparticles deposited on them Such systems facilitate the use of the experimental tools of surface science which are often based on the use of charged particles (ions or electrons) [9, 11,12,13]. Some examples will be discussed to validate this approach
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