Molecular Design of Supported Metal Oxide Catalysts

In Situ Raman Spectroscopy of Supported Transition Metal Oxide Catalysts: 18O2−16O2 Isotopic Labeling Studies

“…The present Raman data also rejects the classical hypothesis for the molecular structure of supported rhenium oxide catalysts, which assumed an isolated trioxo species of the type S-ORe(dO) 3 species with S an oxygen atom of the inorganic oxide. Instead, the molecular structure of supported rhenium oxide catalysts is better described by a polymeric species, in which at least two octahedron-like coordinated Re 7+ are linked together via an oxygen atom.…”

“…[1][2][3] Examples are the dehydrogenation of alkanes over CrO 3 /Al 2 O 3 catalysts, 4 methathesis of olefins over Re 2 O 7 /Al 2 O 3 catalysts 5 and the selective catalytic reduction of NO x over V 2 O 5 /TiO 2 catalysts. 6 Different spectroscopic techniques, such as electron spin resonance (ESR), diffuse reflectance spectroscopy in the UV-vis-near-IR region (DRS), infrared spectroscopy (IR), X-ray absorption spectroscopy (EXAFS-XANES), and Raman spectroscopy (RS), have been extensively used in order to unravel the molecular structure of these catalysts.…”

“…More specifically, it is not yet clear how many terminal MdO bonds are present in these surface molecular entities; in other words, are the supported transition metal oxides present as a monooxo, a dioxo, or a trioxo species? An illustrative example is the limited knowledge about the molecular structure of supported rhenium oxide catalysts, which are generally considered to consist of isolated trioxo species of the type S-O-Re(dO) 3 species with S an oxygen atom of the inorganic oxide. 5 The objective of the present investigation is to resolve this issue by combining in situ Raman spectroscopy with oxygen-18 isotopic labeling studies.…”

The Selective Catalytic Reduction of NOxwith NH3over Titania Supported Rhenium Oxide Catalysts

“…However, there have been no SCR of NO with NH 3 studies on this catalytic system to date. The redox properties of titania supported metal oxide catalysts were probed by methanol oxidation and follow the trend Re ∼ V Cr ∼ Mo ≫ Nb, W, and S (8,19,22,23), which reveals that surface rhenia and vanadia species possess comparable redox activities toward methanol. The selectivites for redox products were in excess of 90% for both surface rhenia and vanadia species on titania, but formaldehyde was exclusively formed with vanadia and formaldehyde as well as methylformate (approximately 3:1 ratio) were formed with rhenia (9,20).…”

“…A titania supported catalyst that possesses very active redox sites (19,20) and surface acid sites in the metal oxide overlayer (21) is the titania supported rhenium oxide system. However, there have been no SCR of NO with NH 3 studies on this catalytic system to date.…”