Aqueous electrochemical insertion of Na into the tungsten oxide hybrid WO3(4,4′-bipyridyl)0.5

Aqueous electrochemical insertion of M⁺ (Na⁺ and H⁺) species into WO₃(4,4′-bipyridyl)_0.5 has been carried out. The chemical states and structure of the resulting product were analysed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). XPS showed the presence of W⁶⁺ as well as the usual reduced W species (W⁵⁺) which is responsible for a change in colour. Moreover, the presence of these intercalates correlates with the evolution of the reduced W species. The bulk structure of the layered hybrid, as determined by powder X-ray diffraction, showed no alteration after electrochemistry, in contrast to the same measurements on tungsten trioxide (WO₃). This however concurs with single-crystal X-ray studies, which show little change in lattice parameters with Na⁺ insertion. Four-probe resistance measurements of the layered hybrid coated film display a drop in resistance after electrochemistry, which can be attributed to the injection of charge-carriers into the conduction band.     

Surface properties of palladium catalysts supported on ternary ZrO2–Al2O3–WOx oxides prepared by the sol–gel method: Study of the chemical state of the support

The surface properties of Pd and Pd–Pt catalysts supported on binary ZrO₂–WOx and ternary ZrO₂–Al₂O₃–WOx oxides prepared by the sol–gel method were studied. Special attention was paid to the study of the texture of the catalysts as well as the chemical state of tungstated zirconia and tungstated zirconia promoted with alumina in the palladium catalysts. The catalysts were tested in the isomerization of n-hexane and were characterized by N₂ physisorption, XRD, TPR, Raman spectroscopy, XPS and FT-IR of adsorbed pyridine. The catalysts had bimodal pore size distributions with mesopores in the range 55–70 Å and macropores of 1000 Å in diameter. The catalysts had a surface WOx coverage (4.4–6.0 W nm^?2) lower than that of the theoretical monolayer (7.0 W nm^?2). A lower acidity of the ternary ZrO₂–Al₂O₃–WOx oxide as compared to the binary ZrO₂–WOx oxide was found. Higher activity in the isomerisation of n-hexane was obtained in the Pd–Pt catalysts supported on ternary ZrAlW oxides prepared by sol–gel that is correlated with the coexistence on the surface of W⁴⁺ (WO₂) or W⁰ and W⁶⁺ (Al₂(WO₄)₃) species, ZrO₂ in the tetragonal phase and a high amount of ZrOx suboxides species in a low oxidation state (Zr³⁺ and Zr²⁺).     

WO3表面的氧缺陷

用不同能量的Ar⁺和H⁺轰击WO₃表面,观察到W_4f峰的位移和加宽。通过谱分解处理得到相应于W_4f电子的W⁶⁺,W⁴⁺和W⁰3个不同的双峰。用表面产生氧缺陷的机理解释了还原过程。UPS谱显示出氧缺陷的存在增加了靠近费密能级处的态密度。H₂O的吸附结果说明WO₃表面的活性与W^{5+< 关键词：}     

Characterization of Cr/SiO2 catalysts and ethylene polymerization by XPS

Cr/SiO₂ catalysts with 1 or 3 wt.% Cr loadings and different chromium precursors were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). A method to determine chromium species in the sample was developed through the decomposition of the Cr 2p XPS spectrum in Cr⁶⁺ and Cr³⁺ standard spectra. The results of the binding energy from the Cr 2p region and of the distribution of chromium species allowed to evaluate the dynamic photo-reduction of the surface chromium species during XPS analysis. Photo-reduction of surface Cr⁶⁺ to Cr³⁺ species was verified for all samples supported in silica, depending on the precursor and chromium content. Bulk CrO₃ and Cr₂O₃ standards did not reveal variation in the binding energy of Cr 2p_3/2, but a physical mixture of CrO₃ with SiO₂ presented photo-reduction. The behavior of this mixture resembled to the catalysts and suggests the participation of the surface hydroxyls of silica in the photo-reduction process. XPS intensity measurements for assessing dispersion of chromium oxide were used to compare the calcined and reduced catalysts to different chromium precursors. Polyethylene chains were detected by in situ XPS, while oligomerization products were not observed.     

Preparation, characterization and photocatalytic activity of multi-walled carbon nanotube-supported tungsten trioxide composites

Multi-walled carbon nanotube (MWCNT)-supported tungsten trioxide (WO₃) composite catalysts were prepared by liquid-phase process. WO₃ nanoparticles grew on the inner and outer surface of MWCNTs. Their photocatalytic activities in the degradation of the Rhodamine B Dye were studied. The effects of mass ratio of MWCNTs to WO₃ were discussed. X-ray diffraction, field emission transmission electron microscopy, thermogravimetric-differential thermal analysis and ultraviolet-visible light absorption spectra were carried out to characterize the composite catalysts. The results indicated that the optimum mass ratio of MWCNTs to WO₃ is 5:100.     

Ordered intermediate compound PtBi-modified Pt/C catalyst for 2-propanol electrooxidation in alkaline medium

The PtBi-modified Pt/C catalyst was prepared by liquid chemical reduction method. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) were used to characterize PtBi-modified Pt/C catalyst. The electrochemical behaviors for the 2-propanol electrooxidation reaction in alkaline medium were measured by cyclic voltammetry, line sweep voltammetry, and electrochemical impedance spectra (EIS). The results showed that the prepared PtBi is ordered intermediate compound. Compared with the spectrum obtained from Pt/C catalyst, the XPS peak of PtBi-modified Pt/C catalyst is obviously moving toward the low Pt 4f biding energy. The Bi⁰ and Bi₂O₃ coexist on the surface of PtBi/C catalyst. In alkaline medium, the electrochemical activity of 2-propanol electrooxidation of PtBi/C catalyst is higher than that of commercial Pt/C catalyst. EIS result shows that the reaction mechanism of 2-propanol electrooxidation for both catalysts is similar.     

Investigations on spectral features of tungsten ions in sodium lead alumino borate glass system

Na₂O–PbO–Al₂O₃–B₂O₃ (NPAB) glasses mixed with different concentrations of WO₃ (ranging from 0 to 2.5 mol%) are synthesized by conventional melt quenching method. The samples are characterized by X-ray diffraction (XRD), optical absorption, Electron paramagnetic resonance (EPR) and Fourier transform infrared (FT-IR) spectroscopic techniques. Glass formation is confirmed by X-ray diffraction spectra. The optical absorption spectra of these glasses exhibited a predominant broad band peak at about 850–870 nm is identified due to d_xy–d_x²_−y² transition of W⁵⁺ ions. From the optical absorption spectral data, optical band gap (E_opt) and Urbach energy (ΔE) are evaluated. From EPR spectra the strength of the signal is increased and hyperfine splitting is resolved with increasing concentration of WO₃ in the glass matrix. The FT-IR spectral studies have pointed out the existence of conventional BO₃, BO₄, B–O–B, PbO₄, WO₄ and WO₆ structural units of these glasses. Various physical properties and optical basicity are also evaluated with respect to the concentration of WO₃ ions.     

Surface electronic structure–catalytic activity relationship of partially reduced WO3 bulk or deposited on TiO2

Catalytic reactions of n-pentane and 1-pentene were carried out as a function of the reduction process of WO₃ as bulk or supported on TiO₂. In situ characterization by XPS–UPS techniques of the different chemical species formed following the reduction processes was performed. At reduction temperatures up to 773 K, two distinct W⁵⁺ and W⁴⁺ states were obtained. The acid functions associated with W⁵⁺, mainly of Brönsted type, enabled to isomerize only 1-pentene to unsaturated products. Dual metal–acid functions (bifunctional) of the W⁴⁺ state perform the isomerization processes of 1-pentene and n-pentane to isopentane in similar way to highly dispersed platinum on alumina catalysts. A conversion of 56% of n-pentane and a selectivity of 87% to isopentane were obtained at 623 K reaction temperature.     

Effect of the excimer laser irradiation on sol–gel derived tungsten–titanium dioxide thin films

A novel technique based on the excimer laser induced crystallization and modification of TiO₂ thin films is being reported. W⁺⁶ ions loaded TiO₂ (WTO) precursor films were prepared by a modified sol–gel method and spin-coated onto microscopic glass slides. Pulsed KrF (248 nm, 13 ns) excimer laser was used to irradiate the WTO amorphous films at various laser parameters. Mesoporous and nanostructured films consisting of anatase and rutile were obtained after laser irradiation at room temperature. The effect of varying W⁺⁶ ions concentrations on structural and optical properties the WTO films was analyzed by X-ray diffraction, field-emission scanning electron microscope, UV-Vis spectrophotometer and transmission electron microscope before and after laser treatment. Films irradiated for 10 pulses at 65–75 mJ/cm² laser fluence, exhibited anatase whereas higher parameters promoted the formation of rutile. XPS results revealed WO₃ along with minor proportion of WO₂ compounds after laser irradiation. Photo-absorbance of the WTO films was increased with increase in W⁺⁶ ions concentration in the film. TEM results exhibited a crystallite size of 15 nm which was confirmed from SEM results as well.     

Investigation on spectral features of tungsten ions in PbO-Bi2O3-As2O3 glass matrix

Lead bismuth arsenate glasses mixed with different concentrations of WO₃ (ranging from 0 to 6.0 mol%) were synthesized. Differential thermal analysis (DTA), optical absorption, ESR and IR spectral studies have been carried out. The results of DTA have indicated that there is a gradual decrease in the resistance of the glass against devitrification with increase in the concentration of WO₃ upto 4.0 mol%.The optical absorption spectra of these glasses exhibited a relatively broad band peaking at about 880 nm identified due to d_xy→d_x²_−y² transition of W⁵⁺ ions; this band is observed to be more intense in the spectrum of glass containing 4.0 mol% of WO₃. Further, two prominent kinks attributed to ³P₀→¹S₀, ¹D₂ transitions of Bi³⁺ ions have also been located in the absorption spectra. The ESR spectra of these glasses recorded at room temperature exhibited an asymmetric signal at g_⊥∼1.71 and g_ll∼1.61. The intensity of the signal is observed to be maximal for the spectrum of the glass W₄. The quantitative analysis of optical absorption and ESR spectral studies have indicated that there is a maximum reduction of tungsten ions from W⁶⁺ state to W⁵⁺ state in the glass containing 4.0 mol% of WO₃. The IR spectral studies have indicated that there is a increasing degree of disorder in the glass network with increase in the concentration of WO₃ upto 4.0 mol%.     

An XPS study of the UV photoreduction of transition and noble metal oxides

The photoreduction of polycrystalline samples of MoO₃, WO₃, Cu₂O, CuO, PdO and PtO by UV irradiation was investigated by X-ray photoelectron spectroscopy (XPS). Photoreduction of these metal oxides was found upon irradiation with the emission lines from a mercury vapor lamp (2537 Å) at room temperature. Other oxides, like ZnO and V₂O₅, where not photoreduced. Mo⁶⁺ and W⁶⁺ were observed to partially photoreduce to Mo⁵⁺ and W⁵⁺. In the case of the copper oxides, both Cu²⁺ and Cu¹⁺ were found to completely photoreduce to the metallic state. The photoreduction of PdO and PtO was observed to proceed slowly through the first few monolayers and was 75% completed within the XPS sampling depth ( ∼ 40 Å) after long irradiation times. All photoreduced species were observed to reoxidize upon exposure to the atmosphere. The oxidation of photoreduced metallic Pt and Pd at room temperature is unique since those metals usually do not oxidize in air. A model has been developed to explain and predict the extent of reduction of metal oxides surfaces by UV irradiation. It shows that depending on band gap and chemical stability, complete or partial reduction of many oxide surfaces can be achieved.     

Synthesis,surface chemistry and electrocatalytic properties of oxygen-modified tungsten carbide in relation to the electrochemical hydrogen oxidation

The surface chemistry of tungsten carbide was studied using an indicator spectrophotometric method and X-ray photoelectron emission spectroscopy. The presence of WO₂, WO₃ and adsorbed polytungstate ions was identified on the surface of WC specimens. The electrocatalytic activity of oxygen-modified tungsten carbide was attributed to the WO₂ at their interface with WC. This conclusion is supported by the presence of some density of states of the 5d, 6s electrons at the Fermi level on the W⁴⁺ and by the relationship between exchange current density and concentration of the lattice O^2?. Insertion of oxygen atoms in the WC crystal lattice leads to a widening of the anodic range of potentials in which the WC maintains its electrochemical activity in hydrogen oxidation reaction.     

COLORATION EFFECT OF PULSED LASER ON WO3

When laser pulses irradiate the surface of the sample WO₃, an interesting coloration effect is obtained. Only by one pulse of XeCl laser irradiation (wavelength: 308 nm, pulse duration: 36 ns, output power: 100 mJ/pulse), a significant color change appears. X-ray photoelectron spectroscopy (XPS) shows that a partial reduction process of WO₃ occurs and conduction band electrons appears. X-ray diffraction pattern indicates that the lattice parameters of the colored samples are increased. A molten layer can be seen in scanning electron microscopy (SEM) image. It may be concluded that the coloration effect of pulsed laser undergoes a process different from that of electro- or photo- chromism, and may be attributed to thermochromism and substoichiometric WO₃ is formed. The coloration process is characterized by its high speed and stability.     

Thermally-induced morphological transition in WOx deposited on a ZrO2(1 0 0) substrate

A combined atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) study of tungsten oxide model catalysts is presented. The model catalysts were prepared by applying the real preparation method to a ZrO₂(1 0 0) single crystal support. AFM imaged several granular structures of scattered dimensions on the surface of ZrO₂(1 0 0) in the as prepared samples. After heating, at low loading the tungsten species rearranged into small WO_x particles strongly interacting with the substrate. At high tungsten content large WO₃ aggregates also formed. XPS analysis confirmed these changes. The estimated surface density of the interacting W-containing species closely matched that of real catalysts.     

Preparation and characterization of the amorphous tungsten cone field emitter arrays by Ar etching

Uniform amorphous tungsten cone arrays in high density were fabricated by Ar⁺ reduction etching of WO₃ nanowire film. The etching process was performed in the analysis chamber of an X-ray photoelectron spectroscopy (XPS) system. SEM and TEM results revealed that the tip radius of the etched cones was 10 nm, and the cones were amorphous with a high aspect ratio of over 250. XPS analysis proved the cones to be metallic tungsten. In the aspect of field-emission property, the tungsten cone arrays had a lower turn-on field of 3 MV m⁻¹ compared with 5 MV m⁻¹ of the as-grown original WO₃ nanowire film.     

Photoluminescence properties and energy transfer of Ca3WO6:Sm3+ co-doped Eu3+

A reddish-orange phosphor, Ca₃WO₆:Sm³⁺, was synthesized by the convenient solid-state reaction method and characterized by X-ray diffraction (XRD). Photoluminescence properties and concentration quenching of Ca₃WO₆:Sm³⁺ phosphor have been discussed in the excitation and emission spectra. Ca₃WO₆:Sm³⁺ phosphor is able to generate a strong excitation peak, which matches the emission wavelength from near-UV LEDs. Energy transfer from Sm³⁺ to Eu³⁺ in Ca₃WO₆ host is observed and investigated in detail. The chromaticity coordinates of Ca₃WO₆:Sm³⁺ can be regulated to approach the NTSC standard values of red phosphor by codoping Eu³⁺ ions. The photoluminescence properties suggest that novel Ca₃WO₆:Sm³⁺, Eu³⁺ phosphor might have a potential application for near-UV LEDs.     

Photoluminescence of Rare Earth Phosphors Na0.5Gd0.5WO4: RE3+ and Na0.5Gd0.5(Mo0.75W0.25)O4: RE3+ (RE=Eu, Sm, Dy)

Two series of phosphors, Na_0.5Gd_0.5WO₄: RE³⁺ and Na_0.5Gd_0.5(Mo_0.75W_0.25)O₄: RE³⁺ (RE?=?Eu, Sm, Dy) have been synthesized by hydrothermal process to obtain the high purity, which have been characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM). The results suggest that Na_0.5Gd_0.5(Mo_0.75W_0.25)O₄: RE³⁺ phosphors are more easily to crystallize than Na_0.5Gd_0.5WO₄: RE³⁺ ones. Both of them present the characteristic luminescence of Eu³⁺, Sm³⁺ and Dy³⁺. Especially the photoluminescent properties of Na_0.5Gd_0.5WO₄: x%Eu³⁺ (Sm³⁺) can be obtained to show white luminescence as the suitable doping concentration of Eu³⁺ or Sm³⁺.     

Ionic to electronic dominant conductivity in Al2(WO4)3 at high pressure and high temperature

Electrical conduction and crystal structure of Al₂(WO₄)₃ at 400 °C have been studied as a function of pressure up to 5.5 GPa using impedance methods and synchrotron radiation X-ray diffraction, respectively. AC impedance spectroscopy and DC polarization measurements reveal an ionic to electronic dominant transition in electrical conductivity at a pressure as low as 0.9 GPa. Conductivity increases with pressure and reaches a maximum at 4.0 GPa, where the conductivity value is 5 orders of magnitude greater than the 1 atm value. Upon decompression, the conductivity retains the maximum value until the sample is cooled at 0.5 GPa. The high pressure-temperature X-ray diffraction results show that the lattice parameters decrease as pressure increases and the crystal structure undergoes an orthorhombic to tetragonal-like transformation at a pressure ∼3.0 GPa. The change of conduction mechanism from ionic to electronic may be explained by means of pressure-induced valence change of W⁶⁺→W⁵⁺, which results in electron transfer between W⁵⁺-W⁶⁺ sites at high pressure.     

Investigations concerning the coexistence of two magnetic phases in mixed crystals (Fe,Mn)WO4

With neutron diffraction, two antiferromagnetic structures were observed simultaneously in a series of mixed crystals(Fe_x, Mn_1?x)WO₄ over a miscibility range of about twenty per cent. X-ray diffraction measurements of lattice constants and line widths showed, that a miscibility gap or fluctuations in concentration can be excluded as a reason for this magnetic behavior. Th e coexistence of two antiferromagnetic phases can be understood on the assumption, that there is only weak interaction between the iron and the manganese ions.The obtained results can be supported by measurements of the susceptibilities of the diamagnetically diluted systems (Fe, Mg)WO₄ and (Mg, Mn)WO₄.     

焙烧温度对SiO2负载的Co3O4纳米粒子表面氧缺陷浓度和CO氧化催化性能的影响

以传统的浸渍法,在不同焙烧温度下制备了用于CO氧化反应的Co₃O₄/SiO₂催化剂．通过激光拉曼光谱(Raman)、X射线光电子能谱(XPS)、X射线衍射(XRD)、程序升温还原(TPR)和X射线吸收精细结构谱(XAFS)表征了该系列催化剂的结构．在所有的催化剂中,XRD和Raman光谱都只检测到了Co₃O₄晶相的存在．与Co₃O₄体相相比,XPS结果表明在200 oC焙烧的(Co₃O₄(200)/SiO₂)催化剂中Co₃O₄表面上存在着过量的Co²⁺．与XPS的结果一致,TPR结果表明Co₃O₄(200)/SiO₂催化剂中Co₃O₄表面上存在氧缺陷, 并且XAFS结果也表明Co₃O₄(200)/SiO₂催化剂中Co₃O₄具有更多的Co²⁺．提高焙烧温度使得过量的Co²⁺进一步氧化为Co³⁺,同时降低了表面氧缺陷浓度,从而得到计量比的Co₃O₄4/SiO₂催化剂．在所有的负载催化剂中Co₃O₄(200)/SiO₂催化剂表现出了最好的CO氧化催化性能,表明过量Co²⁺和表面氧缺陷的存在能够促进Co₃O₄催化CO氧化反应的活性.