Combined UV−vis diffuse reflectance spectroscopy (DRS) and Raman spectroscopy were applied to examine the electronic and molecular structures, respectively, of well-defined W(VI) bulk mixed oxide reference compounds consisting of (i) isolated WO4 or WO6 monomers, (ii) dimeric O3W−O−WO3, (iii) polymeric chain of alternating WO4/WO6 units, and (iv) WO6-coordinated W9−W18 clusters. Raman spectroscopy was employed to confirm the identity and phase purity of the different tungsten oxide structures. UV−vis DRS provided the corresponding electronic edge energy (Eg) of the ligand-to-metal charge transfer (LMCT) transitions of the W(VI) cations. A correlation between the edge energy and the number of covalent bridging W−O−W bonds around the central W(VI) cation was found with Eg linearly decreasing with increasing number of bridging W−O−W bonds. However, a direct relationship between Eg and the domain size, NW, for finite WOx clusters does not exist. Subsequently, UV−vis and Raman spectroscopy information were app...

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Structural determination of bulk and surface tungsten oxides with UV-vis diffuse reflectance spectroscopy and raman spectroscopy

The synthesis of inorganic materials by biological systems is characterized by processes that occur at close to ambient temperatures, pressures and neutral pH. This is exemplified by biosilicification in marine organisms such as diatoms while laboratory-based synthesis of silica involves extreme temperature and pH conditions. We show here that silica and titania particles may be produced by challenging the fungus Fusarium oxysporum with aqueous anionic complexes SiF62− and TiF62− respectively. Extra-cellular protein-mediated hydrolysis of the anionic complexes results in the facile room temperature synthesis of crystalline titania particles while calcination at 300 °C is required for crystallization of silica.

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Fungus-mediated biosynthesis of silica and titania particles

The literature of olefin metathesis by heterogeneous supported catalysts, both industrial-type supported metal oxides (ReOx/Al2O3, ReOx/(SiO2–Al2O3), MoOx/SiO2, MoOx/Al2O3, MoOx/(SiO2–Al2O3), WOx/SiO2, and WOx/(SiO2–Al2O3)) and supported organometallic complexes, is comprehensively reviewed. The focus of this Review is supported metal oxide catalysts, but the well-defined supported organometallic catalyst literature is also covered because such model catalysts have the potential to bridge heterogeneous and homogeneous olefin metathesis catalysis. The recent world shortage of small olefin feedstocks has created renewed interest in olefin metathesis as a route to synthesizing small olefins and is reflected in the recent growth of the patent literature. Despite the extensive application of supported metal oxides in industry for metathesis of small and large olefins, the molecular structures and oxidation states of the catalytic active sites, surface reaction intermediates, and reaction mechanisms of this imp...

/pdf/olefin-metathesis-by-supported-metal-oxide-catalysts-57o0ix2eey.pdf

Olefin Metathesis by Supported Metal Oxide Catalysts

https://www.lehigh.edu/operando/Publications/2006%20Catalysis%20science%20of%20WOx.pdf

Catalysis science of the solid acidity of model supported tungsten oxide catalysts

Very dense and uniformly distributed nitrogen-doped tungsten oxide (WO(3)) nanowires were synthesized successfully on a 4-inch Si(100) wafer at low temperature. The nanowires were of lengths extending up to 5 mum and diameters ranging from 25 to 35 nm. The highest aspect ratio was estimated to be about 200. An emission peak at 470 nm was found by photoluminescence measurement at room temperature. The suggested growth mechanism of the nanowires is vapor-solid growth, in which gaseous ammonia plays a significant role to reduce the formation temperature. The approach has proved to be a reliable way to produce nitrogen-doped WO(3) nanowires on Si in large quantities. The direct fabrication of WO(3)-based nanodevices on Si has been demonstrated.

Nitrogen‐Doped Tungsten Oxide Nanowires: Low‐Temperature Synthesis on Si, and Electrical, Optical, and Field‐Emission Properties

Angle-resolved and depth profiling XPS investigation of a monolayer niobium oxide catalyst

Heterogeneous catalysts with respect to the metathesis of olefins has been prepared by a controlled thermal reaction between W(O-2,6-C 6 H 3 X 2 ) 2 Cl 4 (X = t-Bu, Me, Br, and Cl) or W(MBPD)Cl 4 and a silica support. Surface characteristics of the powder catalysts and a model catalyst have been determined by conventional XPS and Angle-Resolved XPS (AR-XPS). The catalytic activity has been related to the structure of the molecular entities on the surface of the precursor. Furthermore, a model for hydroxylated silica is described. The surface structure ( ? SiO)2W(O-2,6-C 6 H 3 X 2 ) 2 Cl 2 is modeled to determine the preferred arrangement of the tungsten diphenoxide species on the hydroxylated support.

Catalytic activity of supported tungsten phenoxide complexes in olefin metathesis ; XPS characterization ; Application of molecular modelling to surface organometallic chemistry

Ar Bossuyt

Papers

Angle-resolved and depth profiling XPS investigation of a monolayer niobium oxide catalyst

Catalytic activity of supported tungsten phenoxide complexes in olefin metathesis ; XPS characterization ; Application of molecular modelling to surface organometallic chemistry

Olefin metathesis catalyst. Part I. Angle-resolved and depth profiling XPS study of tungsten oxide on silica

Olefin metathesis catalyst.: III. Angle-resolved XPS and depth profiling study of a tungsten oxide layer on silica

Tungsten carbonyl precursors in catalyzed olefin metathesis