Showing papers on "Phosphotungstic acid published in 2008"

Investigation of hybrid molecular material prepared by ionic liquid and polyoxometalate anion

Abstract: A solid hybrid molecular material containing 1-butyl 3-methyl imidazolium cations and Keggin anions of phosphotungstic acid has been synthesized. It is fully characterized by CHN analysis, FTIR, XRD, UV-Vis-NIR DRS, 31P MAS NMR, TGA and SEM. The FTIR spectrum of the compound shows the fingerprint vibrational bands of both Keggin molecular anions and imidazolium cations. The aromatic C-H stretch region (2700–3250 cm−1) of imidazolium cation is split due to the interaction between the ring C-H and bulky Keggin anion. The red-shift in the UV-Vis spectra and the downfield 31P MAS NMR chemical shift also confirm the electrostatic interaction between the ions in the compound. Near IR spectral region (1000–2500 nm) shows the elimination of water in the compound which is hydrophobic.

Phosphotungstic Acid as a Versatile Catalyst for the Synthesis of Fragrance Compounds by α-Pinene Oxide Isomerization: Solvent-Induced Chemoselectivity

Abstract: The remarkable effect of the solvent on the catalytic performance of H3PW12O40, the strongest heteropoly acid in the Keggin series, allows direction of the transformations of alpha-pinene oxide (1) to either campholenic aldehyde (2), trans-carveol (3), trans-sobrerol (4 a), or pinol (5). Each of these expensive fragrance compounds was obtained in good to excellent yields by using an appropriate solvent. Solvent polarity and basicity strongly affect the reaction pathways: nonpolar nonbasic solvents favor the formation of aldehyde 2; polar basic solvents favor the formation of alcohol 3; whereas in polar weakly basic solvents, the major products are compounds 4 a and 5. On the other hand, in 1,4-dioxane, which is a nonpolar basic solvent, both aldehyde 2 and alcohol 3 are formed in comparable amounts. The use of very low catalyst loading (0.005-1 mol %) and the possibility of catalyst recovery and recycling without neutralization are significant advantages of this simple, environmentally benign, and low-cost method. This method represents the first example of the synthesis of isomers from alpha-pinene oxide, other than campholenic aldehyde, with a selectivity that is sufficient for practical usage.

Phosphotungstic Acid Supported on a Nanopowdered ZrO2 as a Filler in Nafion‐Based Membranes for Polymer Electrolyte Fuel Cells

Abstract: An inorganic filler prepared by impregnation of phosphotungstic heteropolyacid on zirconia (HPW/Zr) was developed to be inserted into a perfluorosulphonic polymer matrix for a polymer electrolyte fuel cell (PEFC) operating at a medium temperature (80–120 °C) and low relative humidity (RH). Two different phosphotungstic acid (PWA) loadings (30 and 45% w/w) were anchored on a nanopowdered ZrO2. Such compounds were characterised by different techniques: differential scanning calorimetry (DSC), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and porosity and surface area by Brunauer–Emmett–Teller (BET), to verify the introduction and anchorage of PWA on ZrO2. Two composite Nafion membranes were prepared and characterised in terms of chemical–physical characteristics and electrochemical tests. Thermogravimetric analysis (TGA) provided evidence that HPW/Zr had been incorporated into composite membranes and it was not eluted. A good proton conductivity of about 6 × 10–3 S cm–1 at 120 °C and 25% RH was recorded. Accelerated in situ ageing tests highlighted a good electrochemical stability (more than 150 cycles at 90 °C with dry gases) of the composite membranes with a slow decay and a reasonable integrity of the analysed membrane-electrodes assembly (MEA). Finally, a post-mortem SEM–EDX analysis on MEAs confirmed the presence of HPW/Zr in the membrane after the in situ testing.

Proton-Conducting Glass Electrolyte

Abstract: A new porous glass electrolyte consisting of heteropolyacids, i.e., phosphotungstic acid (PWA) and phosphomolybdic acid, was investigated and was found to yield a remarkably high proton conductivity of 1.014 S cm-1 at 30 °C and 85% relative humidity. This is the first time such a high proton conductivity value has been reported for a heteropolyacid glass membrane. The glass was applied as the electrolyte for an H2/O2 fuel cell, and a maximum power density of 41.5 mW/cm2 at 32 °C was attained using this new PWA-containing electrode.

Single step synthesis of coumarin derivatives over Al-MCM-41 and its supported catalysts under solvent-free condition

Abstract: Al-MCM-41 (Mobil Composition Mater) (Si/Al = 25) molecular sieve was synthesized hydrothermally and 20 and 40 wt% phosphotungstic acid (PW) was supported on it. The materials were characterized using XRD, pyridine adsorbed FT-IR, 31P and 1H MAS NMR techniques. Catalytic performance of the materials was examined in the liquid phase condensation of resorcinol and ethyl acetoacetate. 7-Hydroxy-4-methylcoumarin was the only product observed in this reaction. The results revealed that 20 wt% PW/Al-MCM-41 is found to be more active than other catalysts. The reaction parameters were optimized to obtain high selectivity of the desired product at maximum resorcinol conversion. The reaction was also performed with substituted phenolic derivatives and ethyl acetoacetate in order to realize the substituent effect.

One-step synthesis of silver nanoparticles in self-assembled multilayered films based on a Keggin structure compound

Abstract: Ag nanoparticles (NPs) formed in situ by the photochemical reduction of phosphotungstic acid (H3PW12O40, PTA) under UV-irradiation in polyelectrolyte multilayer nanoreactors composed of poly(ethyleneimine)–silver ions (PEI–Ag+) and PTA fabricated on solid substrates by alternating adsorption, wherein the PTA plays the role of a UV-switchable reducing agent and an assembly reagent. Transmission electron microscopy (TEM) images show the formation of sphere-like silver NPs with sizes smaller than 12 nm in the multilayer films. Atomic force microscopy (AFM) and field emission scanning microscopy (FESEM) imply a film with a rough surface. The UV-vis characteristic absorbances of PTA and Ag NPs increase almost linearly with the number of bilayers, suggesting that the deposition process was regular and highly reproducible from layer to layer. X-Ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) confirm the incorporation of PEI–Ag and PTA into the films. The multilayer films also exhibit good electrocatalytic activity for the oxidation of uric acid, which may be used in electrochemical biosensors.

Membranes and MEAs Based on Sulfonated Poly(ether ketone ketone) and Heteropolyacids for Polymer Electrolyte Fuel Cells

Abstract: Organic sulfonated polyether ketone ketoneSPEKK membranes with different ion-exchange capacities IECs, and composite membranes prepared by the addition of 20 wt % phosphotungstic acid PTA to SPEKK were used to prepare membrane electrode assemblies MEAs. The proton conductivity of the membranes increased with increasing IEC of the SPEKK, and with the addition of PTA. The proton conductivity attained at 80°C and 75% relative humidity was 20 2m S/cm. The feasibility of using SPEKK in the cathode layer of the MEAs was investigated. The electrochemically active surface areas ECAs of the SPEKK-based cathodes were lower than that of the Nafion-based cathode and decreased further as the operating relative humidity was lowered. These observations were reflected in the single-cell polarization data, which indicated that the MEAs with the SPEKK-based electrodes were outperformed by their Nafion-based counterparts. Furthermore, a mismatch in SPEKK IEC between the membrane and cathode resulted in immiscibility at the interface. While the additive stability in the composite membrane was very good, the long-term stability of the membranes was poor when compared to perfluorosulfonic acid membranes such as Nafion, with failure occurring by scission along the gasket edges of the MEA after limited operation.

The effect of Pt oxidation state and concentration on the photocatalytic removal of aqueous ammonia with Pt-modified titania

Abstract: Platinum-modified titanium (IV) oxide (Pt-TiO 2 ) was used to photocatalytically oxidize aqueous ammonia selectively to nitrogen gas. The photocatalyst was solvent deposited on acrylic (PMMA) supports for use in simple distributive reactors. Pt was photodeposited on the titania surface within each reactor with concentrations ranging from 0.4% (w/w) to 5.1% (w/w) Pt. The oxidation state of the deposited Pt was subsequently modified using reduced phosphotungstic acid. Time-dependent kinetic studies were used to demonstrate the effect of oxidation state on the photocatalytic activity of the Pt-TiO 2 . It was determined that treatment with reduced phosphotungstic acid enhanced the reaction rate and selectivity to nitrogen gas of the Pt-TiO 2 photocatalysts. Most significantly, treatment of Pt-TiO 2 with reduced phosphotungstic acid shifts the optimum Pt concentration to higher Pt loadings. The reactor containing 3.2% (w/w) post-treated Pt demonstrated the most favorable combination of NH 3 degradation rate and selectivity to N 2 , resulting in the removal of 28.34% total nitrogen from 1.7 L of a 45.5 ppm NH 3 -N solution within 72 h.

Porous hydrous zirconia supported 12-tungstophosphoric acid catalysts for liquid-phase esterification of 2-ethyl-1-hexanol

Abstract: 12-Phosphotungstic acid supported on porous hydrous zirconia was prepared and characterized by N 2 adsorption isotherm, powder XRD, FTIR, 31 P MAS NMR, H 2 -TPR, NH 3 -TPD, SEM and TEM. It is found that the chemical interaction of Keggin anions with hydrous zirconia is different compared to the interaction with ZrO 2 and Ce 0.5 Zr 0.5 O 2 supports. The phosphotungstic acid clusters dispersed on porous hydrous zirconia did not show any split of IR bands at 1080 cm −1 ( ν P–O ) and 983 cm −1 ( ν W O,ter ) while those dispersed on ZrO 2 and Ce 0.5 Zr 0.5 O 2 showed a split in these two bands due to the lowering of symmetry of the central PO 4 tetrahedron and direct interaction of W O ter with oxide support. The dispersion of phosphotungstic acid on porous hydrous zirconia led to the growth of crystallites which showed catalytic activity for liquid-phase esterification of 2-ethyl-1-hexanol with acetic acid. Both conversion of 2-ethyl-1-hexanol and selectivity for 2-ethyl-1-hexyl acetate can be achieved at 100%.

Heteropoly Acid Electrolytes for Double-Layer Capacitors and Pseudocapacitors

Abstract: Two heteropoly acids, phosphotungstic acid (PWA) and silicotungstic acid (SiWA), were studied as aqueous electrolytes for applications on electrochemical storage devices. Their performance was compared to the H 2 SO 4 benchmark with respect to both double-layer and pseudocapacitance using cyclic voltammetry, electrochemical impedance spectroscopy, and self-discharge measurements. Both heteropoly acids showed a very good proton conductivity in aqueous solutions, with overall performance comparable to H 2 SO 4 . Therefore, in spite of their electrochemical active nature, PWA and SiWA are feasible as electrolytes provided the operation window is chosen appropriately.

Oxidation Desulfurization of Thiophene Using Phase Transfer Catalyst/H2O2 Systems

Abstract: In our study, an effective phosphomolybdic acid/hexadecyltrimethyl-ammonium bromide catalyst for oxidative desulfurization of thiophene in a model compound was formed. The oxidation activities of thiophene for a series of heteropoly acids were estimated. The results show that the oxidation activity of thiophene increased with increasing oxidation time, oxidation temperature, and the volume of 30% H2 O2 oxidant. The optimal values are 150 min, 40°C, and 3 mL, and sulfur removal attained 96.3% when phosphotungstic acid/hexadecyltrimethylammonium bromide was used as a catalyst.