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Effects of SO2 and H2O on low-temperature NO conversion over F-V2O5-WO3/TiO2 catalysts
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Effect of water in a non-aqueous electrolyte on electrochemical Mg2+ insertion into WO3
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Data from Reactive Species and Reaction Pathways for the Oxidative Cleavage of 4-Octene and Oleic Acid with H2O2 over Tungsten Oxide Catalysts
Oxidative cleavage of carbon–carbon double bonds (C═C) in alkenes and fatty acids produces aldehydes and acids valued as chemical intermediates. Solid tungsten oxide catalysts are low cost, nontoxic, and selective for the oxidative cleavage of C═C bonds with hydrogen peroxide (H2O2) and are, therefore, a promising option for continuous processes. Despite the relevance of these materials, the elementary steps involved and their sensitivity to the form of W sites present on surfaces have not been described. Here, we combine in situ spectroscopy and rate measurements to identify significant steps in the reaction and the reactive species present on the catalysts and examine differences between the kinetics of this reaction on isolated W atoms grafted to alumina and on those exposed on crystalline WO3 nanoparticles. Raman spectroscopy shows that W–peroxo complexes (W–(η2-O2)) formed from H2O2 react with alkenes in a kinetically relevant step to produce epoxides, which undergo hydrolysis at protic surface sites. Subsequently, the CH3CN solvent deprotonates diols to form alpha-hydroxy ketones that react to form aldehydes and water following nucleophilic attack of H2O2. Turnover rates for oxidative cleavage, determined by in situ site titrations, on WOx–Al2O3 are 75% greater than those on WO3 at standard conditions. These differences reflect the activation enthalpies (ΔH‡) for the oxidative cleavage of 4-octene that are much lower than those for the isolated WOx sites (36 ± 3 and 60 ± 6 kJ·mol–1 for WOx–Al2O3 and WO3, respectively) and correlate strongly with the difference between the enthalpies of adsorption for epoxyoctane (ΔHads,epox), which resembles the transition state for epoxidation. The WOx–Al2O3 catalysts mediate oxidative cleavage of oleic acid with H2O2 following a mechanism comparable to that for the oxidative cleavage of 4-octene. The WO3 materials, however, form only the epoxide and do not cleave the C–C bond or produce aldehydes and acids. These differences reflect the distinct site requirements for these reaction pathways and indicate that acid sites required for diol formation are strongly inhibited by oleic acids and epoxides on WO3 whereas the Al2O3 support provides sites competent for this reaction and increase the yield of the oxidative cleavage products.
Materials Data on W4NO12 by Materials Project
(WO3)8N2 crystallizes in the trigonal P-31m space group. The structure is three-dimensional and consists of three ammonia molecules and one WO3 framework. In the WO3 framework, there are two inequivalent W+5.25+ sites. In the first W+5.25+ site, W+5.25+ is bonded to six O2- atoms to form corner-sharing WO6 octahedra. The corner-sharing octahedra tilt angles range from 0–28°. There are a spread of W–O bond distances ranging from 1.87–2.02 Å. In the second W+5.25+ site, W+5.25+ is bonded to six O2- atoms to form corner-sharing WO6 octahedra. The corner-sharing octahedra tilt angles range from 0–28°. There are a spread of W–O bond distances ranging from 1.87–2.02 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to two equivalent W+5.25+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two equivalent W+5.25+ atoms. In the third O2- site, O2- is bonded in a linear geometry to two W+5.25+ atoms. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent W+5.25+ atoms. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent W+5.25+ atoms.
Materials Data on W2O7 by Materials Project
(WO3)4O2 crystallizes in the cubic Fd-3m space group. The structure is three-dimensional and consists of eight water molecules and one WO3 framework. In the WO3 framework, W is bonded to six equivalent O atoms to form corner-sharing WO6 octahedra. The corner-sharing octahedral tilt angles are 37°. All W–O bond lengths are 1.94 Å. O is bonded in a bent 150 degrees geometry to two equivalent W atoms.
Materials Data on W3NO9 by Materials Project
(WO3)6N2 crystallizes in the hexagonal P6_3/mcm space group. The structure is three-dimensional and consists of two ammonia molecules and one WO3 framework. In the WO3 framework, W5+ is bonded to six O2- atoms to form corner-sharing WO6 octahedra. The corner-sharing octahedra tilt angles range from 0–29°. There are a spread of W–O bond distances ranging from 1.87–2.02 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent W5+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two equivalent W5+ atoms.
Materials Data on W2NO6 by Materials Project
(WO3)4N2 crystallizes in the cubic Fd-3m space group. The structure is three-dimensional and consists of eight ammonia molecules and one WO3 framework. In the WO3 framework, W+4.50+ is bonded to six equivalent O2- atoms to form corner-sharing WO6 octahedra. The corner-sharing octahedral tilt angles are 36°. All W–O bond lengths are 1.94 Å. O2- is bonded in a bent 150 degrees geometry to two equivalent W+4.50+ atoms.
Materials Data on PH24W12C6N3O40 by Materials Project
(WO3)12((CH3)2NH2)3PO4 crystallizes in the trigonal R-3m space group. The structure is zero-dimensional and consists of eighteen dimethylazanium molecules, six phosphoric acid molecules, and six WO3 clusters. In each WO3 cluster, there are three inequivalent W sites. In the first W site, W is bonded in a 5-coordinate geometry to five O atoms. There is one shorter (1.73 Å) and four longer (1.95 Å) W–O bond length. In the second W site, W is bonded in a 5-coordinate geometry to five O atoms. There are a spread of W–O bond distances ranging from 1.74–1.95 Å. In the third W site, W is bonded in a 5-coordinate geometry to five O atoms. There are a spread of W–O bond distances ranging from 1.74–1.95 Å. There are nine inequivalent O sites. In the first O site, O is bonded in a bent 120 degrees geometry to two equivalent W atoms. In the second O site, O is bonded in a bent 150 degrees geometry to two equivalent W atoms. In the third O site, O is bonded in a bent 120 degrees geometry to two equivalent W atoms. In the fourth O site, O is bonded in a bent 150 degrees geometry to two W atoms. In the fifth O site, O is bonded in a single-bond geometry to one W atom. In the sixth O site, O is bonded in a single-bond geometry to one W atom. In the seventh O site, O is bonded in a bent 120 degrees geometry to two W atoms. In the eighth O site, O is bonded in a bent 150 degrees geometry to two equivalent W atoms. In the ninth O site, O is bonded in a single-bond geometry to one W atom.
Structure-Activity Relationships of Hydrothermally Aged Titania-Supported Vanadium-Tungsten Oxide Catalysts for SCR of NOx Emissions with NH3
Supported V2O5-WO3/TiO2 materials employed as selective catalytic reduction (SCR) catalysts for NOx emission control from power plants. Fresh SCR catalysts usually receive exposure to harsh treatments in industry to accelerate catalyst activation (calcination in air at 650oC) and catalyst aging (hydrothermal aging at 650oC) in a way that represents various points in the catalyst/product lifetime. The present study investigates the catalyst structural and chemical changes occurring during such harsh treatments. Three series of supported V2O5-WO3/TiO2 catalysts were prepared by incipient-wetness impregnation of aqueous ammonium metavanadate and metatungstate precursors. The catalysts were subsequently dried and calcined at 550oC in O2, 650oC in O2, and hydrothermal conditions (10% O2, 8% H2O, 7% CO2 and 75% N2) at 650oC. The resulting catalysts were physically characterized by numerous techniques (in situ Raman, in situ IR, in situ High Field-High Spinning solid-state 51V MAS NMR, in situ EPR, XRD, BET surface area and ICP) and chemically probed with adsorbed ammonia, SCR-TPSR, and the SCR reaction. The surface WOx sites on the TiO2 support behave as a textural promoter that stabilizes the TiO2 (anatase) phase from sintering and transforming to the undesirable crystalline TiO2 (rutile) phase that can lead to formation of a Ti1-xVxO2 (rutile) solid solution with reduced V4+ cations (~7-15%). The surface VOx sites are mostly oligomerized as surface V+5Ox sites (~50-85% oligomers) and the extent of oligomerization tends to increase with surface WOx coverage and calcination temperature. A major difference between the calcined and hydrothermally treated catalysts was the low concentration of surface NH3* species on Lewis acid sites for the hydrothermally treated catalysts, yet the SCR activity was almost comparable for both catalysts. This finding suggests that surface NH4+*, primarily associated with the surface VOx sites, are able to efficiently perform the SCR reaction. Given that multiple catalyst parameters were simultaneously varying during these treatments, it was difficult to correlate the SCR activity with any single catalyst parameter. A correlation, however, was found between the SCR TOF/activity and the sum of the surface NH3* and NH4+* species, which is dominated by the surface NH4+* species.
Direct Observation of Tungsten Oxidation Studied by In Situ Environmental TEM
In this study, in situ environmental transmission electron microscopy (ETEM) was applied, for the first time, to investigate the thermal oxidation of a pristine and a self-ion irradiated polycrystalline tungsten, using a MEMS-based gas cell at 500 oC to 900 oC in a 1 bar 2%O2/N2 gas mixture. By tracking the dynamic evolution of the tungsten oxide scale as it initiates, grows, and sublimates during a consecutive thermal oxidation experiment, we observed two distinctive tungsten oxide microstructure – one nanocrystalline o-WO3 scale grown on W{27-1 } and W{1-1 8} and another o-WO3 scale exhibits a novel highly textured nanostructure. While the two oxide microstructures shared a similar thickness of ~200 nm after 40-minute early-stage oxidation, the nanocrystalline scale on the W{27-1 } grew much more rapidly at 800 oC than the highly textured oxide at a higher temperature of 900 oC. This suggests both the microstructure of these tungsten oxide scales as well as their oxidation kinetics are highly sensitive to the tungsten surface orientation, and such correlations also change dynamically in the course of oxidation. We also discuss the tungsten oxidation mechanism, the effects of the TEM foil thickness, and the focused ion beam (FIB) Ga+ damage on in situ ETEM oxidation.
Materials Data on AlWO3 by Materials Project
WO3Al is (Cubic) Perovskite structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional and consists of one aluminium molecule and one WO3 framework. In the WO3 framework, W3+ is bonded to six O2- atoms to form corner-sharing WO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.00 Å) and two longer (2.05 Å) W–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to two equivalent W3+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two equivalent W3+ atoms. In the third O2- site, O2- is bonded in a linear geometry to two equivalent W3+ atoms.
Materials Data on WO5 by Materials Project
WO5 crystallizes in the monoclinic P2_1 space group. The structure is one-dimensional and consists of four hydrogen peroxide molecules and two WO3 ribbons oriented in the (0, 1, 0) direction. In each WO3 ribbon, W is bonded in a 5-coordinate geometry to five O atoms. There are a spread of W–O bond distances ranging from 1.73–2.18 Å. There are three inequivalent O sites. In the first O site, O is bonded in a distorted trigonal planar geometry to three equivalent W atoms. In the second O site, O is bonded in a single-bond geometry to one W atom. In the third O site, O is bonded in a single-bond geometry to one W atom.
Addition of oxygen to and distribution of oxides in tantalum alloy T-111 at low concentrations
Oxygen was added at 820 and 990 C at an oxygen pressure of about .0003 torr. The technique permitted predetermined and reproducible oxygen doping of the tantalum alloy (T-111). Based on the temperature dependency of the doping reaction, it was concluded that the initial rates of oxygen pickup are probably controlled by solution of oxygen into the T-111 lattice. Although hafnium oxides are more stable than those of tantalum or tungsten, analyses of extracted residues indicate that the tantalum and tungsten oxides predominate in the as-doped specimens, presumably because of the higher concentrations of tantalum and tungsten in the alloy. However, high-temperature annealing promotes gettering of dissolved oxygen and oxygen from other oxides to form hafnium oxides. Small amounts of tantalum and tungsten oxides were still present after high temperature annealing. Tungsten oxide (WO3) volatilizes slightly from the surface of T-111 at 990 C but not at 820 C. The vaporization of WO3 has no apparent effect on the doping reaction.
Dissolution kinetics of small amounts of oxygen in tantalum alloy T-111 and internal oxide displacement reactions during annealing
Oxygen was added to T-111 (Ta-8W-2Hf, wt. %) at 820 and 990 C at an oxygen pressure of about 0.0003 torr. The technique employed permitted predetermined and reproducible doping of T-111 up to 3.0 at. % oxygen. Based on the temperature dependence of the doping reaction, it is concluded that the initial rates of oxygen pickup are probably controlled by solution of oxygen into the T-111 lattice. Although hafnium oxides are more stable than those of tantalum or tungsten, analyses of extracted residues indicate that the latter oxides predominate in the as-doped specimens, presumably because of the higher concentrations of tantalum and tungsten in the alloy. However, high-temperature annealing promotes gettering of dissolved oxygen and of other oxides to form hafnium oxides. Small amounts of tantalum and tungsten oxides were still present after high-temperature annealing. Tungsten oxide (WO3) volatilizes slightly from the surface of T-111 at 990 C. The vaporization of WO3 has no apparent affect on the doping reaction.
Garnet melt viscosity, surface tension and drainage
Good surface morphology and layer uniformity of LPE-grown Bi YIG films are favored by fast melt removal after growth. Three flux modifying oxides: MoO3, V2O3, and WO3 are compared with respect to their effect on viscosity, surface tension and melt drainage. All three oxides increased the viscosities of Bi-garnet melts, but the viscosities and drainage times of V2O3 and MoO3 modified melts were smaller than those of WO3 modified melts. The liquid-gas surface tension was found to be temperature independent. The drainage process was strongly temperature dependent, 40 to 60 kcal/mol, whereas the viscosities of melts had activation energies of 11 to 16 kcal/mol. Contact angles of 16 + or - 2 deg were measured on frozen melt drops.
Solid-state reprogrammable analog resistive devices for electronic neural networks
The fabrication and performance of WO3-based, solid-state, three-terminal device configurations as programmable analog memory elements are reported. These transistorlike device structures exhibit good resistance progammability with a remarkable resolution of a few percent of the resistive strength over a four orders of magnitude dynamic range. The most critical component of these devices is an insulating layer between the active WO3 and the cation donor layer. The progamming characteristics and operation mechanisms of the device are described, and probable reaction mechanisms critical to the device stability are discussed.
Work Functions for Models of Scandate Surfaces
The electronic structure, surface dipole properties, and work functions of scandate surfaces have been investigated using the fully relativistic scattered-wave cluster approach. Three different types of model surfaces are considered: (1) a monolayer of Ba-Sc-O on W(100), (2) Ba or BaO adsorbed on Sc2O3 + W, and (3) BaO on SC2O3 + WO3. Changes in the work function due to Ba or BaO adsorption on the different surfaces are calculated by employing the depolarization model of interacting surface dipoles. The largest work function change and the lowest work function of 1.54 eV are obtained for Ba adsorbed on the Sc-O monolayer on W(100). The adsorption of Ba on Sc2O3 + W does not lead to a low work function, but the adsorption of BaO results in a work function of about 1.6-1.9 eV. BaO adsorbed on Sc2O3 + WO3, or scandium tungstates, may also lead to low work functions.