摘要 :
A series of pure and aluminum (Al) doped WO3 powders were synthesized at low temperature. The as synthesized materials have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible...
展开
A series of pure and aluminum (Al) doped WO3 powders were synthesized at low temperature. The as synthesized materials have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-VIS) spectroscopy and color difference meter, respectively. A relation was found between the color difference and the UV-VIS photochromic activity. Moreover, the optical band gap of the as-prepared powder narrowed due to the appearance of impurity levels as the Al3+ ions migrated into the WO3 crystal lattice. Some rod-like particles have been found to decrease with the increase of Al concentration. An optimum Al concentration was found to be 0.25% to present the best UV-light induced photochromic activity. The mechanism of photochromic process of the Al-doped WO3 powders has been discussed in detail based on the characterization results. (C) 2015 Elsevier B.V. All rights reserved.
收起
摘要 :
Two different photo-catalysts consisting of tungsten oxide supported on zirconia and niobia have been studied. The photoactivity of the samples has been investigated in both the absence and presence of H2O2 for the photo-oxidation...
展开
Two different photo-catalysts consisting of tungsten oxide supported on zirconia and niobia have been studied. The photoactivity of the samples has been investigated in both the absence and presence of H2O2 for the photo-oxidation of 4-nitrophenol in aqueous suspensions and compared to that of WO3 and of the pure ZrO2 and Nb2O5 supports. Both catalysts were found to be photoactive, although no beneficial influence of the presence of tungsten oxide on the reaction rate was observed in the absence of H2O2. The presence of hydrogen peroxide was observed to be beneficial for all of the samples. Scanning electron microscopy, X-ray diffraction, diffuse reflectance and laser Raman spectroscopies, surface area and porosity determination, as well as Fourier transform infra-red spectroscopy monitoring of surface acidity were used to characterize the catalysts. [References: 34]
收起
摘要 :
The oxidation of primary and secondary alcohols to their corresponding carbonyl compounds proceeds with high efficiency under molecular oxygen in the presence of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and tungsten oxide/ alumina (WO...
展开
The oxidation of primary and secondary alcohols to their corresponding carbonyl compounds proceeds with high efficiency under molecular oxygen in the presence of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and tungsten oxide/ alumina (WO3/Al2O3). The method is environmentally benign, because the reaction requires only molecular oxygen as the terminal oxidant and gives water as a side product Various aromatic, alicyclic, and aliphatic alcohols can be converted to their corresponding carbonyl compounds in excellent yields. It is noteworthy that the oxidative transformation of the alcohols proceeds chemoselectively in the presence of other functional groups. In addition, a plausible catalytic pathway is proposed.
收起
摘要 :
The paper proposes a new theoretical model based on local thermodynamic equilibrium enabling the prediction of gas generation during the reaction of aluminum-based thermites. We demonstrate that the model has the capability to pre...
展开
The paper proposes a new theoretical model based on local thermodynamic equilibrium enabling the prediction of gas generation during the reaction of aluminum-based thermites. We demonstrate that the model has the capability to predict the total pressure and the partial pressures of its components as a function of the reaction extent and compaction. Al/CuO, Al/Bi2O3, Al/Sb2O3, Al/MoO3, and Al/WO3 thermites are modeled and their capability to generate pressure is compared. Simulation results are also validated through dedicated experiments and show general agreement beyond the state of the art. Mechanisms underlying pressure generation are detailed. A two-stage process for the pressure increase in Al/CuO reaction, also observed experimentally, is shown to be driven by oxygen generation as produced by CuO and Cu2O vaporization through different kinetics. Comparison with experimental data stresses the issue of understanding the complex chemical processes taking place during vaporization and subsequent gas phase reactions and the need to determine their thermodynamic constants.
收起
摘要 :
We report the dramatic manipulation of an oxide interface in Al2O3/WO3 from insulating to metallic state by creating a two-dimensional conducing path. The WO3 thin film is deposited on the SiO2 grown Si substrate using radio frequ...
展开
We report the dramatic manipulation of an oxide interface in Al2O3/WO3 from insulating to metallic state by creating a two-dimensional conducing path. The WO3 thin film is deposited on the SiO2 grown Si substrate using radio frequency magnetron sputtering and the amorphous Al2O3 layer is formed by atomic layer deposition on the WO3 layer. After rapid vacuum annealing at 400 degrees C, the interfacial conducing path of Al2O3/WO3 reveals an abnormally high sheet carrier density of 4.91 x 10(16) cm(-2) compared with < 10(9) cm(-2) for bare WO3. The X-ray photoelectron spectroscopy (XPS) shows that WO3 is partially reduced; and a W5+ oxidation state is observed at the interface. The schematic electronic band diagram of the interfacial region obtained by combined XPS and ultraviolet photoelectron spectroscopy analyses indicates that the downward band bending at the surface of WO3 induces a confined electron accumulation at the interface. Synergetic effects between the increased unpaired W 5d electrons in the W5+ oxidation state and the accumulative charge confinement at the Al2O3/WO3 interfaces lead to a two-dimensional conducing path. The metallic conduction is distinct from the insulating bulk properties. This study demonstrates an example of a short-range-ordered two-dimensional conducing path at two insulating oxide interfaces formed at low temperature, which is applicable to flexible oxide conductors with great conduction path stability.
收起
摘要 :
Catalysts containing 10wt.% W were prepared using Al2O3-HY mixed supports with various HY contents. The catalytic performance of these catalysts for the metathesis of ethene and 2-butene to propene was determined in a fixed-bed fl...
展开
Catalysts containing 10wt.% W were prepared using Al2O3-HY mixed supports with various HY contents. The catalytic performance of these catalysts for the metathesis of ethene and 2-butene to propene was determined in a fixed-bed flow reactor at 180degreesC under 0.1 MPa. The 2-butene conversion of these catalysts increases remarkably with the HY content in the range of 0-30 Between 30 and 70wt.% of HY content, the conversion reaches a plateau of 60-63%, which is very close to the thermodynamic equilibrium value of similar to64%. After that, the 2-butene conversion decreases substantially. The propene, selectivity shows the similar trends. The maximum propene selectivity goes up to 88%. By the studies of NH3-TPD, H-2-TPR and UV-vis, the role of HY zeolite in the 10W/Al2O3-xHY is explained in two following aspects: (i) changing the Bronsted acidity of catalysts, which may affect the formation of initial carbene species; (ii) modifying the interaction between W species and support for the formation of active centers with intermediate oxidation number (W4+, W5+, W((6-y))(+) (0 < y < 1)). Based on this information, the optimal HY content for 10W/Al2O3-xHY catalysts is about 50-70%. (C) 2004 Elsevier B.V. All rights reserved.
收起
摘要 :NiO/Al2O3–TiO2/WO3 catalysts for acid catalysis were prepared by the addition of Al2O3 and the modification with WO3. The strong acid sites were formed through the bonding between dispersed WO3 and TiO2. The larger the dispersed ...
展开
NiO/Al2O3–TiO2/WO3 catalysts for acid catalysis were prepared by the addition of Al2O3 and the modification with WO3. The strong acid sites were formed through the bonding between dispersed WO3 and TiO2. The larger the dispersed WO3 amount, the higher both the acidity and catalytic activity. The addition of Al2O3 up to 5 mol% enhanced acidity and catalytic activity of NiO/Al2O3–TiO2/WO3 gradually due to the interaction between Al2O3 and TiO2 and consequent formation of Al–O–Ti bond. The presence of NiO may attract reactants and enhance the local concentration of reactants near acid sites and consequently increase catalytic activity.
收起
摘要 :
In the past decades, as an alternative to traditional sputtering deposition process, atmospheric pressure solution-based deposition (APSD), considered as a cost-effective method for the construction of nanostructured electro-chrom...
展开
In the past decades, as an alternative to traditional sputtering deposition process, atmospheric pressure solution-based deposition (APSD), considered as a cost-effective method for the construction of nanostructured electro-chromic (EC) films with improved EC performance, is widely studied. However, the inadequate EC performance of the films, especially the poor cycle stability, impedes the development of solution-processed EC films. This paper reports excellent EC performance results for WO3 quantum-dots films prepared by a common APSD process with either Li+ or Al3+ electrolyte: a large optical contrast (97.8% and 94.1% at 633 nm), a fast switching speed (4.5 s and 13.5 s for coloring, 4 s and 10 s for bleaching) and an ultralong cycle life (10000 cycles with 10% optical contrast loss and 20000 cycles without degeneration at 633 nm). The excellent EC performance can be attributed to the ultrasmall size in all three-dimensions and no organic overlayer of WO3 quantum dots, which would greatly shorten the diffusion paths of intercalation ions, decrease interface barrier, provide fast charge-transport and electron-transfer kinetics and high reaction rates. Trivalent Al3+, as an alternative to common monovalent insertion ions (H+, Li+, Na+), was proven to be as an effective insertion ion for WO3 quantum dots. Compared with Li+ electrolyte, the films possess longer cycle life in Al3+ electrolyte, which can be attributed to the smaller ionic radius and the ability to support multi-electron redox reactions of Al3+. This research is an important first step for the fabrication of inexpensive EC smart windows, and should shape the future research on solution-based processes.
收起
摘要 :
Strong solid acid catalysts,NiO/Al2O3-TiO2/WO3 for ethylene dimerization were prepared by the addition of Al2O3 and the modification with WO3.The acid sites and acid strength were increased by the inductive effect of WO3 species b...
展开
Strong solid acid catalysts,NiO/Al2O3-TiO2/WO3 for ethylene dimerization were prepared by the addition of Al2O3 and the modification with WO3.The acid sites and acid strength were increased by the inductive effect of WO3 species bonded to the surface of catalysts.The larger the dispersed WO3 amount,the higher both the acidity and catalytic activity for ethylene dimerization.The addition of Al2O3 to TiO2 up to 5 mol% enhanced acidity and catalytic activity gradually due to the interaction between Al2O3 and TiO2 and consequent formation of Al-O-Ti bond.
收起
摘要 :
? 2023 Elsevier B.V.WO3 is a promising active material for electrochromic application. In this study, 5% Al2O3 doped WO3 layers were investigated. The thickness of the deposited material was measured as 132 nm and the refractive i...
展开
? 2023 Elsevier B.V.WO3 is a promising active material for electrochromic application. In this study, 5% Al2O3 doped WO3 layers were investigated. The thickness of the deposited material was measured as 132 nm and the refractive index at 550 nm wavelength was measured as 1.92. The band gap energy of the doped material was calculated by the Tauc-Plot method and it was found as 3.95 eV. Electrochromic (EC) measurements of the material were obtained in the voltage range of ?0.6 V to +0.6 V. The intercalated/de-intercalated charge amounts into the material were calculated as 0.40 mC and 0.14 mC, respectively. It was observed that colored time was 14 s and bleaching time was determined as 20 s. The material was performed to a 300-cycle test. That is, 5% Al2O3 doped WO3 layers is promising material for the EC application.
收起
原文获取