Showing papers on "Phosphotungstic acid published in 2009"

Synthesis and characterization of mesoporous phosphotungstic acid/TiO2 nanocomposite as a novel oxidative desulfurization catalyst

Abstract: A series of mesoporous phosphotungstic acid/TiO 2 (HPW/TiO 2 ) nanocomposites with various HPW contents have been synthesized by evaporation-induced self-assembly method. These nanocomposites were used as catalysts for oxidative desulfurization of model fuel, which was composed of dibenzothiophene (DBT) and hydrocarbon, and used H 2 O 2 as oxidant. These catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm, transmission electron microscopy (TEM), FTIR and UV–vis. Characterization results suggest that these mesoporous HPW/TiO 2 possessed relatively uniform channel-like pores with Barrett–Joyner–Halenda (BJH) pore size of about 4 nm. The Brunauer–Emmett–Teller (BET) surface of the mesoporous HPW/TiO 2 slightly increases with the increase of HPW content and reach to a peak value of 176 m 2 /g and 0.25 cm 3 /g when the HPW content is 30 wt%. Keggin-type heteropolyacids (HPAs) has been encapsulated into anatase TiO 2 framework and the average size of TiO 2 nanoparticles is 8 nm. Catalytic oxidation results show that the catalysts are very active in refractory bulky molecule organosulfur compounds in fuel oil. The oxidative removal of DBT increases as the HPW content increases. The mesoporous HPW/TiO 2 also shows high selectivity for DBT oxidation in the DBT–petroleum ether–benzene system. The selective desulfurization ratio reach to 95.2% with mesoporous HPW/TiO 2 (20 wt%) catalyst under the reaction condition of 333 K, 2 h. In addition, the mesoporous HPW/TiO 2 catalyst shows excellent reusing ability, which makes it a promising catalyst in oxidative desulfurization process.

Deep Oxidative Desulfurization of Fuels Catalyzed by Phosphotungstic Acid in Ionic Liquids at Room Temperature

Abstract: A simplified extraction and catalytic oxidative desulfurization (ECODS) system composed of phosphotungstic acid (H3PW12O40·14H2O), 30% H2O2, and [bmim]BF4 was found suitable for the deep removal of sulfur in model oil. By this desulfurization system dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT), and benzothiophene (BT) could be effectively removed. Removal of DBT could reach 98.2% at room temperature (30 °C) for 1 h, which was remarkably superior to mere solvent extraction with IL (14.2%) or catalytic oxidation without IL (15.9%). When the reaction temperature increased to 70 °C, treatment of BT, DBT, and 4,6-DMDBT with our ECODS system showed 100% removal of sulfur compounds in 3 h. This desulfurization system could be recycled five times with slight decrease in activity.

Immobilization of phosphotungstic acid (PTA) on imidazole functionalized silica: evidence for the nature of PTA binding by solid state NMR and reaction studies

Abstract: Phosphotungstic acid (PTA) immobilized onto imidazole functionalized fumed silica and was used as an efficient catalyst for epoxidation of a variety of olefins using aqueous H2O2 as an oxidant. Negligible leaching of PTA under the reaction conditions employed indicates a strong interaction between PTA and imidazole. The immobilized catalysts could be separated and reused after the catalytic cycle. Evidence for the heterogenization of PTA on the imidazole functionalized fumed silica has been inferred from different spectroscopic techniques like IR, UV−vis, and NMR. Importantly, the nature of binding of PTA on the support has been studied in detail by solid state NMR spectroscopy using 15N labeled imidazole support. It is clear from the NMR studies that the effective heterogenization of PTA is mainly due to imidazolium ion formation on the support by the acidic protons of PTA and the resultant ion pair.

A new mixed-matrix membrane for DMFCs

Abstract: A new mixed-matrix membrane based on stabilized phosphotungstic acid (PTA) incorporated to chitosan (CS)-hydroxy ethyl cellulose (HEC) for application in direct methanol fuel cells (DMFCs) is reported. Membranes are characterised using Fourier Transform Spectroscopy (FTIR), Thermo-Gravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and their mechanical properties are evaluated. The PTA content in the CS-HEC blend and its influence on proton conductivity, water/methanol sorption, and methanol cross-over in the DMFC is studied. The DMFC with 3 wt. % stabilized PTA-CS-HEC mixed-matrix membrane delivers peak power-density of 58 mW/cm2 at a load current-density of 210 mA/cm2 with a lower methanol cross-over than that observed for a DMFC operating with a Nafion membrane electrolyte.

Cs exchanged phosphotungstic acid as an efficient catalyst for liquid-phase Beckmann rearrangement of oximes

Abstract: Cs exchanged phosphotungstic acid is a highly efficient and environmentally benign solid acid catalyst for the liquid-phase Beckmann rearrangement of ketoximes to the corresponding amides The catalysts Cs x H 3− x PW 12 O 40 ( x = 15, 2, 25 and 3) were prepared by a titration method The characterization results indicated that the primary Keggin structure remained intact after exchanging the protons with Cs ions Moreover, the Cs exchanged catalysts were insoluble and exhibited larger BET surface area than the parent acid The catalysts exhibited high reactivity and selectivity for the formation of ɛ-caprolactam, the precursor of Nylon 6, from cyclohexanone oxime The catalyst can be recovered after reaction without any structural transformation

Layer-by-layer electrochemical assembly of poly(diphenylamine)/phosphotungstic acid as ascorbic acid sensor

Abstract: A layer-by-layer (LbL) film assembly was constructed that comprises alternative layers of poly(diphenylamine) (PDPA) and phosphotungstic acid (PTA). First, a layer of oxidized PDPA (referred to as PDPA(+)) was deposited by electropolymerization. Then, a layer of negatively charged PTA was deposited on the PDPA(+) layer . This processes was repeated several times to obtain multilayer LbL film (PDPA/PTA)n, where n is the number of double layers. The LbLs were characterized by UV-Vis spectroscopy, FT-IR spectroscopy and X- ray diffraction spectroscopy. The process of formation of the LbL assembly was monitored by electrochemical methods. Electrochemical studies revealed that this LbL film possesses a remarkable electrocatalytic activity towards oxidation of ascorbic acid in neutral aqueous medium. The enhanced electrocatalytic activity of (PDPA/PTA)n LbL film is attributed to the existence of tungsten atoms in the interlayers of PDPA.

A Solvent-Free Synthesis of Coumarins Using Phosphotungstic Acid as Catalyst

Abstract: Phosphotungstic acid (PTA) is used an efficient catalyst for the von Pechmann condensation reaction of phenols and β-keto esters under solvent-free conditions. This method was compared with those of the reactions in the different solvents and catalysts. The methodology presented offers significant improvements for the synthesis of coumarins with regard to yield of products, simplicity in operation and green aspects by avoiding toxic conventional catalysts and solvents. Phosphotungstic acid (PTA) is used an efficient catalyst for the von Pechmann condensation reaction of phenols and β-keto esters under solvent-free conditions. This method was compared with those of the reactions in the different solvents and catalysts. The methodology presented offers significant improvements for the synthesis of coumarins with regard to yield of products, simplicity in operation and green aspects by avoiding toxic conventional catalysts and solvents.

Phosphotungstic acid: an efficient, cost-effective and recyclable catalyst for the synthesis of polysubstituted quinolines.

Abstract: Phosphotungstic acid (H(3)PW(12)O(40)) was used as an efficient and recyclable catalyst for the synthesis of polysubstituted quinolines through the Friedlander condensation of 2-aminoarylketone with carbonyl compounds, which was achieved by conventional heating under solvent-free conditions.

Synthesis and Characterization of Proton Conducting Inorganic−Organic Hybrid Nanocomposite Membranes Based on mixed PWA-PMA-TEOS-GPTMS-H3PO4-APTES for H2/O2 Fuel Cells

Abstract: A series of novel fast proton conductive inorganic−organic nanocomposite hybrid membranes doped with a mixture of phosphotungstic acid (PWA) and phosphomolybdic acid (PMA) have been prepared by sol−gel process with 3-glycidoxypropyltrimethoxysilane (GPTMS), 3-aminopropyltriethoxysilane (APTES), phosphoric acid (H3PO4), and tetraethoxysilane (TEOS) as precursors. These hybrid membranes were studied with respect to their structural, thermal, elastic moduli, and proton conductivity properties. The X-ray diffraction measurement revealed the amorphous nature of the hybrid membranes. The Fourier transform infrared spectroscopy has shown a good complexation of H3PO4 in the membrane matrix and the both characteristic Keggin anions PW12O403− and PMo12O403− were present in the nanocomposite membranes. Thermal analysis including thermogravimetric and differential thermal analysis confirmed that the membranes were thermally stable up to 300 °C. Thermal stability of the membranes was significantly enhanced by the pres...

Proton-conducting membranes from phosphotungstic acid-doped sulfonated polyimide for direct methanol fuel cell applications

Abstract: A series of novel hybrid proton conducting membranes based on sulfonated naphthalimides and phosphotungstic acid (PTA) were prepared from N-Methyl Pyrrolidone (NMP) solutions. These hybrid organic-inorganic materials, composed of two proton-conducting components, have high ionic conductivities (9.3 × 10−2 S cm−1 at 60 °C, 15% PTA), and show good performance in H2|O2 polymer electrolyte membrane fuel cells (PEMFC), previously reported by us. Moreover, they have low methanol permeability compared to Nafion®112. In this paper we describe, for the first time, the behaviour of these hybrid membranes as electrolyte in a direct methanol fuel cell (DMFC). The maximum power densities achieved with PTA doped sulfonated naphthalimide membrane, operating with oxygen and air, were 34.0 and 12.2 mW cm−2, respectively; about the double and triple higher than those showed by the non-doped membrane at 60 °C.

PWA/silica/PFSA composite membrane for direct methanol fuel cells

Abstract: A novel composite membrane was prepared by incorporation of silica-included phosphotungstic acid (PWA) additive into perfluorosulfonic acid (PFSA) followed by solution casting. Physico-chemical properties of the composite membranes were studied by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry analysis (TGA), water uptake and swelling ratio. The results of FT-IR and TGA illustrated the stability of the PWA-silica additive in the PFSA matrix. Lower PWA-silica additive loading (2.5 and 5 wt%) in the composite membranes helped to inhibit methanol crossover and enhance the proton conductivity. However, higher additive content shows decrease in both methanol resistance and proton conductivity.

Preparation of 1-butyl-3-methylimidazolium dodecatungstophosphate and its catalytic performance for esterification of ethanol and acetic acid

Abstract: 1-Butyl-3-methylimidazolium dodecatungstophosphate catalyst ([bmim]3PW12O40) with high water tolerance was prepared from 1-butyl-3-methylimidazolium bromide ([bmim]Br) and phosphotungstic acid (H3PW12O40). The catalyst was characterized by means of Fourier transform infrared spectroscopy, thermogravimetry-differential scanning calorimetry, n-BuNH2 potentiometric titration, elemental analysis and so on. Its catalytic activity for esterification of ethanol and acetic acid to ethyl acetate was measured. The results show that there were three crystal-water molecules in the [bmim]3PW12O40 catalyst, and it preserved the primary Keggin structure and acid strength of H3PW12O40. The acid amount of [bmim]3PW12O40 catalyst was less than that of H3PW12O40. The [bmim]3PW12O40 catalyst exhibited higher catalytic activity and reusability in the esterification of ethanol and acetic acid to ethyl acetate.

Proton-conducting composite membranes from graft copolymer electrolytes and phosphotungstic acid for fuel cells

Abstract: New organic–inorganic composite membranes based on poly(vinylidene fluoride-co-chlorotrifluoroethylene)-graft-poly(styrene sulfonic acid) [P(VDF-co-CTFE)-g-PSSA] with embedded phosphotungstic acid (PWA) were prepared. Fourier transform infrared spectra indicated the existence of a specific interaction between P(VDF-co-CTFE)-g-PSSA graft copolymer and PWA particles. PWA nanoparticles were well confined in the polymeric matrix up to 20 wt.%, above which they started to be extracted from the matrix, as revealed by scanning electron microscope analysis. Accordingly, Young’s modulus of membranes also increased with PWA concentration up to 20 wt.%, above which it continuously decreased. Upon incorporation of PWA nanoparticles, the proton conductivity of composite membranes slightly decreased from 0.042 to 0.035 S/cm at room temperature up to 20 wt.%, presumably due to strong interaction between the sulfonic acids of graft copolymer and PWA nanoparticles. The characterization by thermal gravimetric analysis demonstrated the enhancement of thermal stabilities of the composite membranes with increasing concentration of PWA.

Sulphonated poly ether ether ketone/ polyvinyl alcohol/phosphotungstic acid composite membranes for pem fuel cells *

Abstract: Composite membranes with polyvinyl alcohol (PVA), sulphonated poly ether ether ketone (SPEEK) and phosphotungstic acid (PWA) were prepared using solvent casting method. The proton conductivities of such membranes were found to be in the order of 10–3S/cm in the fully hydrated condition at room temperature as measured by impedance spectroscopy. The crystalline properties were studied by X-ray diffraction analysis. The thermal properties were determined by TGA and DSC techniques. The tensile strength and percentage elongation were obtained from UTM studies. Water and methanol uptake of these membranes were studied.

Hydroformylation of 1,4-Diacetoxy-2-butene Using HRh(CO)(PPh3)3 Tethered on Alumina as a Catalyst: Kinetic Study

Abstract: Hydroformylation of 1,4-diacetoxy-2-butene (DAB) was studied using [HRh(CO)(PPh 3 ) 3 ] complex catalyst tethered on alumina using phosphotungstic acid (PTA) as an anchoring agent, with the aim to understand the product distribution, selectivity, and intrinsic kinetics. It was observed that with the tethered heterogeneous catalyst a simultaneous hydroformylation followed by deacetoxylation steps was possible, which is relevant for combining two steps in the sequence of synthesis of vitamin-A intermediate [2-formyl-4-acetoxy butene (FAB)]. 31 P cross-polarization magic angle spinning nuclear magnetic resonance (CP MAS NMR) and infrared (IR) instrumental techniques were found be the most effective techniques to establish the catalyst structure and true heterogeneity. On the basis of the spectroscopic evidence, we postulate the loss of a PPh 3 group during tethering to give HRh(CO)(PPh 3 ) 2 -PTA-Al 2 O 3 as a heterogeneous complex catalyst. Experimental data on the concentration-time and CO/H 2 consumption-time profiles were obtained and the effects of DAB concentration, CO partial pressure, H 2 partial pressure, and catalyst loading were studied in a 50 mL stirred batch reactor over a temperature range of 338-358 K. The analysis of solid-liquid-gas mass transfer effects was investigated to ensure that the reaction was operating in the kinetic regime. Various models were developed, and the best model was chosen by a model discrimination procedure. The agreement between the model prediction and the experimental data was found to be excellent. The activation energies for the hydroformylation and deacetoxylation steps were found to be 42.5 and 80.2 kJ/mol.

Preparation of silica-based proton conductors for intermediate temperature fuel cells

Abstract: The ternary system SiO2-P2O5-ZrO2 electrolyte and phosphotungstic acid (PWA) doped SiO2-P2O5-ZrO2 electrolyte were prepared for intermediate temperature fuel cell by using sol-gel technique These silica-based proton conductors were confirmed to be non-crystalline structure without phase separation and good thermal stability by XRD and TG/DTA analysis The doped PWA was found to be stabilized within the silica matrix and to enhance the proton conductivity The proton conductivities of SiO2-P2O5-ZrO2 and SiO2-P2O5-ZrO2-PWA electrolytes showed 33×10−5 and 18×10−3 S/cm at 90 °C, respectively, and the cell performance of SiO2-P2O5-ZrO2-PWA electrolyte was obtained as 002–025 mA/cm2 at 300 °C under humid condition