Addition Of WO3 Research Articles

Selective catalytic reduction of NOx with H2 over WO3 promoted Pt/TiO2 catalyst

Pt/TiO2 and WO3 modified Pt/TiO2 catalysts have been investigated for the selective catalytic reduction of NOx by H2 (H2-SCR) in the presence of oxygen. It was found that the addition of WO3 leads to a significant promoting effect on the low-temperature activity of Pt/TiO2 catalyst and the optimal loading is 2%. X-ray absorption near-edge structure (XANES) revealed the electron transfer from WO3 to Pt active sites, leading to the formation of metallic Pt, which is responsible for the low-temperature H2-SCR of NOx. In-situ DRIFTS demonstrated that the introduction of WO3 to Pt catalyst not only contributes to the formation of reactive adsorbed NOx species on the catalyst, but also promotes the formation of NH4+ species. All of these factors, collectively, account for the improved low-temperature activity of Pt-WO3/TiO2 catalyst.

Performance of RP-3 kerosene cracking over Pt/WO3–ZrO2 catalyst

A series of WO3–ZrO2 composite oxides were prepared by co-precipitation and their catalytic performances for the RP-3 kerosene cracking were investigated. These composite oxides were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), N2 adsorption–desorption measurement, X-ray diffraction (XRD), and NH3-temperature programmed desorption (NH3-TPD). The results showed that the addition of WO3 could effectively inhibit the phase transformation of ZrO2 from tetragonal phase to monoclinic phase. Among all as-prepared samples, the support composed of WO3 (4wt%)–ZrO2 exhibited the largest surface area, the strongest surface acidity, and the most concentrated strong acidic density. Additionally, the gas amount of catalytic cracking over Pt/WO3 (4wt%)–ZrO2 catalyst at the temperature region 650–700°C was about 1.5 times higher than that of thermal cracking. After the composite oxides were calcined at 800°C for 3h, they almost lost their catalytic activities.

Sunlight responsive WO3/ZnO nanorods for photocatalytic degradation and mineralization of chlorinated phenoxyacetic acid herbicides in water

Highly effective WO3/ZnO nanorods (NRs) were synthesized via a hydrothermal–deposition method for degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under natural sunlight. The structural properties of WO3/ZnO NRs such as morphology, crystal structure, porous properties and light absorption characteristics were investigated in detail. The X-ray diffraction and X-ray photoelectron spectroscopy results indicated that the prepared samples were two-phase photocatalysts consisted of WO3 and ZnO NRs. The UV–vis diffuse reflectance spectroscopy result showed that the addition of WO3 altered the optical properties of the photocatalysts. In contrast with the pure ZnO NRs, commercial anatase TiO2 and commercial WO3, the WO3/ZnO NRs showed excellent sunlight photocatalytic activities in degrading 2,4-D. The optimal WO3 loading and calcination temperature were also determined. Based on the band position, the synergetic effect of WO3 and ZnO NRs was the source of the enhanced photocatalytic activity as validated by PL and terephthalic acid-photoluminescence measurements. The reaction intermediates and degradation pathways of 2,4-D were elucidated by a HPLC method. In addition, the extent of mineralization during the 2,4-D degradation was also estimated using total organic carbon (TOC) and ion chromatography (IC) analyses.

Efficient production of propylene in the catalytic conversion of glycerol

Vapor-phase catalytic conversion of glycerol into propylene was performed over Cu/Al2O3 and acid-loaded Cu/Al2O3 catalysts in an H2 flow at ambient pressure. Acidic substances such as WO3, MoO3, V2O5 and H3PO4 were loaded on a commercial Cu/Al2O3. The addition of WO3 was found to be effective for promoting the formation of 1-propanol and propylene from glycerol, and 9.3wt% WO3-loaded Cu/Al2O3 (WO3/Cu/Al2O3) catalyst showed the best catalytic performance. WO3/Cu/Al2O3 calcined at a low temperature of 320°C had the largest number of acid sites and gave a 1-proponol selectivity of 38.2% and a propylene selectivity of 47.4% in an H2 flow at 250°C. The catalytic reaction of glycerol was performed over double-bed catalysts, in which WO3/Cu/Al2O3 was charged in the upper bed and a commercial silica–alumina was charged in the lower bed, to promote the conversion of 1-propanol into propylene. A high propylene selectivity of 84.8% was obtained over the double-bed catalysts at 100% glycerol conversion. An efficient catalytic process for the production of propylene from glycerol was proposed.

Activity and characterization of a Ce–W–Ti oxide catalyst prepared by a single step sol–gel method for selective catalytic reduction of NO with NH3

A Ce–W–Ti mixed oxide catalyst prepared by a single step sol–gel method exhibited excellent SCR activity and high resistance to H2O and SO2. The excellent catalytic performance might be attributed to the improved dispersion of Ce species on TiO2, the increase in the amount of Ce3+ and chemisorbed oxygen and the strong interaction among ceria, tungsten and titania owing to the addition of WO3.

Influence of WO3‐Doping on the Microstructure and Electrical Properties of ZnO–Bi2O3 Varistor Ceramics Sintered at 950°C

The phase evolution, microstructure, and electrical properties of WO3‐doped ZnO–Bi2O3‐based varistors were investigated for different amounts x (0 ≤ x ≤ 1.60 mol%) of the dopant. When x was less than 0.40, the dissolved W6+ in the β‐Bi2O3 acted as a donor in the grain boundaries and reduced the electrical properties of the ZnO varistors. However, when x was 0.40 mol%, which meant an amount of WO3 equal to that of Bi2O3, the electrical properties dramatically increased, which means the W6+ donor effect is removed at the grain boundaries because a new Bi2WO6 phase was formed in the grain‐boundary regions. The Bi2WO6 phase has high oxygen conductivity at high temperatures; it transfers more oxygen to the grain boundaries in order to further enhance the electrical properties. For x values higher than 0.40 (i.e., an addition of WO3 that is greater than the content of Bi2O3), the electrical properties were steadily reduced in comparison to the composition with x = 0.40. This could be explained by the reduced amount of Co, Mn, and Al at the grain boundaries and in the ZnO grains as a result of their incorporation into the ZnWO4 phase. The electrical properties of the ZnO grains and the grain boundaries were in agreement with the results of the impedance spectroscopy analysis.

Nitrogen dioxide (NO2) sensing performance of p-polypyrrole/n-tungsten oxide hybrid nanocomposites at room temperature

Polypyrrole (PPy)–tungsten oxide (WO3) hybrid nanocomposite have been successfully synthesized using different weight percentages of tungsten oxide (10–50%) dispersed in polypyrrole matrix by solid state synthesis method. The sensor based on PPy–WO3 was fabricated on glass substrate using cost effective spin coating method for detection of NO2 gas in the low concentration range of 5–100ppm. The gas sensing performance of hybrid material was studied and compared with those of pure PPy and WO3. It was found that PPy–WO3 hybrid nanocomposite sensor can complement the drawbacks of pure PPy and WO3. The structure, morphology and surface composition properties of PPy–WO3 hybrid nanocomposites were employed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The presence of WO3 in PPy matrix and their interaction was confirmed using XRD, FTIR techniques. The porous surface morphology was observed with addition of WO3 in PPy matrix which is useful morphology for gas sensing applications. TEM image of PPy–WO3 hybrid nanocomposites shows the average diameter of 80–90nm. X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical composition of nanocomposites. It was observed that 50% WO3 loaded PPy sensor operating at room temperature exhibit maximum response of 61% towards 100ppm of NO2 gas and able to detect low concentration of 5ppm NO2 gas with reasonable response of 8%. The hybrid sensor shows better sensitivity, selectivity, reproducibility and stability compared to pure PPy and WO3. The proposed sensing mechanism of hybrid nanocomposite in presence of air and NO2 atmosphere was discussed with the help of energy band diagram. Furthermore, the interaction of NO2 gas with PPy–WO3 hybrid nanocomposites sensor was studied by cole–cole plot using impedance spectroscopy.

Conversion of ethanol over transition metal oxide catalysts: Effect of tungsta addition on catalytic behaviour of titania and zirconia

Ethanol dehydration was investigated at atmospheric pressure with 1.43h−1 WHSV in nitrogen, in the temperature range 423–773K over titania and zirconia, as such and modified by addition of WO3. As for comparison, data on other WO3-free and WO3-containing catalysts are also discussed: a strong Lewis acid (alumina), a covalent oxide (silica) and a basic material (calcined hydrotalcite). The catalysts were characterized using FT-IR of adsorbed pyridine and of wolframate species, and by UV–vis spectroscopy. The results presented here show that WO3/ZrO2 and WO3/TiO2 are excellent catalysts for ethanol dehydration. Their performances may compete with those of zeolites and alumina for conversion to diethyl ether and to ethylene. The addition of WO3 to both ZrO2 and TiO2 introduces strong Brønsted acid sites that are supposed to represent the active sites in the reaction, but also inhibits the formation of byproducts, i.e. acetaldehyde and higher hydrocarbons. This is attributed to the poisoning of basic sites and of reducible surface Ti and Zr centres, respectively.

Effects of Increasing Tungsten on Structural, Elastic and Optical Properties of xWO3–(40−x)Ag2O–60Te2O Glass System

Ternary tellurite glasses with composition of xWO3(40−x)Ag2O–60TeO2 (x = 0–40 mol%) have been prepared by melt-quenching method. Elastic and optical properties of the glass system were obtained by ultrasonic velocity measurements and UV–vis spectroscopy, respectively, while structural investigation was carried out by using Raman spectroscopy. The longitudinal and shear velocities, vL and vs showed large increase at x from 0 to 20 mol% before decrease with further addition of WO3. Independent longitudinal modulus CL and shear modulus μ bulk modulus Ke Young's modulus Y and Debye temperature θD showed similar behaviors to both velocities. The large increase of the elastic moduli at x from 0 to 20 mol% is suggested to be due to the increase in WO6 octahedral unit structure indicating the increase of bridging oxygen (BO) and formation of stronger Te–O–W bonds compared to Te–O–Te bonds. On the other hand, for x > 20 mol%, the decrease in the elastic moduli was due to the increase of non-bridging oxygen (NBO) as a result of formation of WO4 tetrahedral via breaking Te–O–W network. Further analysis by using bulk compression and ring deformation models showed a slight decrease in the ratio of ideal bulk modulus Kbc to the experimental bulk modulus Ke and average atomic ring size, l for x 20 mol%. Our analysis also indicates that limited ring deformation took place and the main compression mechanism in this glass system was mainly ideal isotropic compression. On the other hand, optical band gap Eopt showed small variation for x = 0–20 mol% but decreased upon higher WO3 content while refractive index n showed the opposite trend. This optical behavior is suggested to be related to the changes in cross link density and NBO concentration in the glass system.

Synthesis and Characterization of WO3 Doped TiO2 Particle/Nanowire Layer in Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have been intensively studied since their discovery; however, a number of problems remain to be solved in order to enhance their efficiency. In particular, one of the main limiting factors is the electron recombination that occurs due to contact between the transparent conductive oxide and the redox electrolyte. In this work, we report an improvement in the photovoltaic characteristics of dye-sensitized solar cells by using mixtures of TiO2, TiO2 nanowires (TNWs), and WO3. DSSCs were constructed by application of WO3 mixed with a composite of varying percentages of TiO2 nanoparticle and TNWs. The addition of WO3 reduces the surface trap states of TiO2, improving its power conversion efficiency by suppressing charge recombination, and increasing the driving force of electron injection. A DSSC fabricated using a TiO2–WO3 mixture was found to have a maximum conversion efficiency of 5.47% owing to the effective prevention of electron recombination. As a result, DSSCs based on TiO2–WO3 mixtures exhibited better photovoltaic performance compared to cells fabricated from pure TiO2

Investigations of thermal, structural and optical properties of tellurite glass with WO3 adding

Tellurite glasses with the molar composition (89-x) TeO2–10TiO2–1Nd2O3–xWO3 (x=0, 10 and 20mol%) were prepared by the conventional melt-quenching technique. The effects of WO3 concentration on the structural, thermal and optical properties of tellurite glasses have been discussed. From the differential scanning calorimetry measurements, thermal properties such as glass transition temperature Tg, crystallization temperature Tx, and thermal stability ΔT are estimated. It was found that ΔT increases with the increase of WO3 composition which can indicate a reinforcement of the glassy network. Both Raman and FTIR results show that the addition of WO3 induced a depolymerisation of tellurite glass since the Te–O–Te inter-chain linkages are progressively substituted by stronger Te–O–W bridges that are at the origin of the increase of the thermal stability of the glass.The optical band gap energy values corresponding to the direct and indirect allowed transitions and the Urbach energy values of the prepared tellurite glasses have been calculated from optical absorption edges. The results show an important decrease of the optical band gap with the increase of WO3 concentration. It was assigned to W6+ ions that could have a role as network modifier. The Urbach energy was found to decrease with WO3 compositions which suggest the possibility of long range order. The refractive index and extinction coefficient were obtained by spectroscopic ellipsometry. Higher values for the refractive index are recorded due to the high polarizability of non-bridging oxygen. It is observed also that the refractive index, n increases with increasing WO3 content. It is established that there is a trend by which the energy gap decreases with increasing refractive index and increasing the polarizability of the oxide ions. The complex dielectric function ε, relative to each sample, was estimated from regression analysis. The material studied here has potential application as optical fiber.

Effect of ZnO–WO3 additives on sintering behavior and microwave dielectric properties of 0.95MgTiO3–0.05CaTiO3 ceramics

The effect of WO3 addition on the phase formation, the microstructures and the microwave dielectric properties of 1wt% ZnO doped 0.95MgTiO3–0.05CaTiO3 ceramics system were investigated. Formation of second phase MgTi2O5 could be effectively restrained through the addition of WO3, but should be in right amount. WO3 as additives could not only effectively lower the sintering temperature of the ceramics to 1310°C, but also promote the densification. A dielectric constant εr of 20.02, a Q×f value of 62,000 (at 7GHz), and a τf value of −5.1ppm/°C were obtained for 1wt% ZnO doped 0.95MgTiO3–0.05CaTiO3 ceramics with 0.5wt% WO3 addition sintered at 1310°C.

Soft-chemical synthesis, characterization and humidity sensing behavior of WO3/TiO2 nanopowders

Tungsten oxide/titania (WO3/TiO2) nanopowders were synthesized by the polymeric precursor method which varied the WO3 content between 0 and 10mol%. The powders were thermally treated in a conventional furnace and their structural, microstructural and electric properties were evaluated by X-ray diffraction (XRD), Raman spectrometry, N2 physisorption, NH3 chemisorption, temperature-programmed reduction (TPR), X-ray absorption near-edge spectroscopy (XANES) in situ XANES and extended X-ray absorption fine structure spectroscopy (EXAFS) and transmission electron microscopy (TEM). XRD and Raman spectrometry confirmed the homogeneous distribution of an amorphous WO3 phase in the TiO2 matrix which stabilized the anatase phase through the generation of [TiO5·V0] or [TiO5·V0] complex sites. Conventional TPR-H2 (temperature programmed reduction) along with XANES TPR-H2 and XANES TPR-EtOH showed that WO3/TiO2 sample reduction occurs through the formation of these complex clusters. Moreover, the addition of WO3 promoted an increase in the surface acidity of doped samples as revealed by NH3 chemisorption. The WO3/TiO2 bulk-ceramic samples were further used to estimate their potential application in a humidity sensor in the range of 15–85% relative humidity. Probable reasons that lead to the different humidity sensor responses of samples were given based on the structural and surface characterizations. Correlation between the sensing performance of the sensor and its structural features are also discussed. Although all samples responded as a humidity sensor, the W2T sample (2mol% added WO3) excelled for sensitivity due to the increase in acid sites, optimum mean pore size and pore size distribution.

Enhancement of elastic properties by WO3 partial replacement of TeO2 in ternary (80 − x)TeO2–20PbO–xWO3 glass system

Tellurite–tungsten (80−x)TeO2–20PbO–xWO3 (x=0–20mol%) glass with concurrent reduction of TeO2 and addition of WO3 was prepared by the melt-quenching method. Elastic and structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo overlap method at 5MHz and Fourier Transform Infrared (FTIR) spectroscopy, respectively. Both longitudinal modulus (L) and shear modulus (G) showed a slight decrease at x=5mol% followed by a large and almost linear increase for x>5mol%. Interestingly, bulk modulus (K), Young's modulus (E) and hardness (H) recorded almost similar trends where the values showed large increase for x>5mol%. At x=20mol% the elastic moduli increased by more than 30% compared to binary 80TeO2–20PbO glass. FTIR analysis showed an increase in intensity of TeO4 assigned peaks concurrent with the decrease in intensity of TeO3 assigned peaks for x>5mol% which indicates an increase in number of bridging oxygen (NBO) and a decrease in non-bridging oxygen (BO), respectively. The enhancement of L, G and other related moduli for x>5mol% is suggested to be due to the increase in BO which caused the increase in rigidity and stiffness of the glass network. Quantitative analysis based on bulk compression and ring deformation models showed kbc/ke ratio monotonously decreased from 2.69 (x=5mol%) to 2.09 (x=20mol%) which infers that the glass system became a relatively more open 3D network for x>5mol% WO3 addition.

Ordered mesoporous tungsten oxide and titanium oxide composites and their photocatalytic degradation behavior

Highly ordered mesoporous WO3/TiO2 (MWTs) composite materials with tunable chemical compositions were obtained by a surfactant template-assisted evaporation-induced self-assembly (EISA) processes. The structure properties of the MWT materials were characterized by small angle XRD, TEM and N2 sorption. The resultant materials showed large amount of ordered mesopores and high chemical homogeneity. With increasing crystallinity degree, the order degrees of mesostructure turned worse gradually. The MWT hybrids exhibited excellent visible light response due to the addition of WO3 with narrow band gap. Photocatalytic performances of the MWT samples were determined by measuring the photo-degradation of rhodamine B dye and phenol under simulated solar light irradiation. The effect of material parameters such as surface area, crystallinity and chemical compositions in the binary heterostructured system on photocatalytic performance were discussed in details.

Kinetics of Glycerol Dehydration with WO3/TiO2in Supercritical Water

Dehydration of glycerol on TiO2 and WO3/TiO2 in supercritical water at 400 °C and 33 MPa was examined using a fixed bed flow reactor. The structure of TiO2 was changed from anatase type to rutile type in supercritical water, and addition of WO3 to TiO2 suppressed the change of structure. Main products were acrolein and acetaldehyde. In the reaction on TiO2, a large amount of propionic acid was also produced. The reaction route was proposed on the basis of the products distribution from glycerol and intermediate products. From kinetic analysis, the reaction route could explain the experimental data well. Because of high water density, degradation of acrolein to acetaldehyde is favorable in supercritical water. Reaction rate for dehydration of glycerol to acrolein considerably increased with an increase in WO3 content of the catalyst, and this dependence is attributed to higher surface area and stronger acidity of WO3/TiO2 catalysts.

Nano-WO3 film modified macro-porous silicon (MPS) gas sensor

We prepared macro-porous silicon (MPS) by electrochemical corrosion in a double-tank cell on the surface of single-crystalline P-type silicon. Then, nano-WO3 films were deposited on MPS layers by DC facing target reactive magnetron sputtering. The morphologies of the MPS and WO3/MPS samples were investigated by using a field emission scanning electron microscope. The crystallization of WO3 and the valence of the W in the WO3/MPS sample were characterized by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The gas sensing properties of MPS and WO3/MPS gas sensors were thoroughly measured at room temperature. It can be concluded that: the WO3/MPS gas sensor shows the gas sensing properties of a P-type semiconductor gas sensor. The WO3/MPS gas sensor exhibits good recovery characteristics and repeatability to 1 ppm NO2. The addition of WO3 can enhance the sensitivity of MPS to NO2. The long-term stability of a WO3/MPS gas sensor is better than that of an MPS gas sensor. The sensitivity of the WO3/MPS gas sensor to NO2 is higher than that to NH3 and C2H5OH. The selectivity of the MPS to NO2 is modified by deposited nano-WO3 film.

Investigation of low loss Z-type hexaferrites for antenna applications

Z-type hexaferrites in series (Ba0.5Sr0.5)3Co2Fe24O41 + xWO3 (where x = 0.0, 0.1, 0.2, 0.3, and 0.4 wt. %) were prepared by a conventional ceramic technique. The addition of WO3 has been used to enhance sintering density and magneto-dielectric properties of low loss Co2Z ferrites. A second phase of BaWO4 can be found in the XRD patterns. The replacements of hexagonal phase by high valence W6+ ions improved sintering and accelerated density of the ferrites, which resulted in the increase of real permeability. Due to the formation of Fe2+, excessive WO3 resulted in undesired high permittivity and dielectric loss tangent. Comparatively, a ferrite sample with 0.2 wt. % WO3 gave the best performances in terms of density, microstructure, magneto-dielectric property, and loss tangent. Since loss tangent was kept low with the frequency ranging from 10 to 300 MHz, such magneto-dielectric material could be used in this frequency range for antenna applications.

Development of Iridium Catalysts for Selective Reduction of NO with CO

The development of Ir/SiO2-based catalysts for the selective reduction of NO with CO in the presence of O2 is described in this review paper. The catalytic activity of Ir/SiO2 was promoted considerably by addition of Nb2O5 and WO3. These promoted catalysts showed NO reduction activity even in the absence of SO2, in contrast to Ir/SiO2 catalyst. The addition of Nb2O5 was found to stabilize Ir metal as the active species for NO reduction. Also in the case of WO3, it was concluded that Ir metal interacting strongly with WO3 (denoted as Ir–WO3) is the catalytic active species. High temperature calcination created preferentially the Ir–WO3 species. The catalytic activity and durability of Ir/WO3/SiO2 was further promoted by addition of Ba. The developed Ba/Ir/WO3/SiO2 catalyst in monolithic form showed good performance for NO reduction for actual diesel exhaust.

Acid and redox properties of tungstated zirconia catalysts

Various tungstated zirconia catalysts with a WO3 loading of about 16 wt% were characterized both in their acid and oxidation properties. The samples have been characterized in their micro-structural and surface properties by BET, X-ray diffraction, Raman spectroscopy, temperature programmed reduction, elemental chemical analysis. The surface acidity was determined by the techniques of NH3 adsorption microcalorimetry and pyridine infrared spectroscopy (FT-IR). Improved acidity has been detected upon addition of WO3 to zirconia by both techniques. The global acid strength and the total number of acid sites increased greatly with the formation of WOx clusters on the zirconia support. This acidity increase can be attributed to the creation of Bronsted acid sites generated by the well dispersed WOx domains, as observed by FT-IR pyridine desorption.