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Showing papers on "Phosphotungstic acid published in 2002"


Journal ArticleDOI
TL;DR: In this paper, a comprehensive study on the effect of HPWA loading on the acidity has been performed using pyridine adsorption, NH3 TPD and a catalytic test reaction.
Abstract: Phosphotungstic acid (HPWA)–silica composites were synthesised upto 80 wt.% HPWA loading both by conventional impregnation and sol–gel incorporation techniques. The samples were characterised by BET, XRD, NMR, FT-IR and TG. A comprehensive study on the effect of HPWA loading on the acidity has been performed using pyridine adsorption, NH3 TPD and a catalytic test reaction. The samples containing 50 wt.% HPWA showed the best overall performance. Although, the acidic properties of the impregnated catalysts were superior to their sol–gel counterparts, stability measurements (XRD, FT-IR and test reaction) performed before and after washing the samples with H2O/EtOH mixture have unambiguously proved that the sol–gel derived composites are more suitable for the purposes of heterogeneous catalysis.

75 citations


Patent
16 Jan 2002
TL;DR: In this paper, economic processes for the production of component for refinery blending of transportation fuels by selective oxidation of feedstocks comprising a mixture of hydrocarbons, sulfur-containing and nitrogen-containing organic compounds are disclosed.
Abstract: Economical processes are disclosed for the production of component for refinery blending of transportation fuels by selective oxidation of feedstocks comprising a mixture of hydrocarbons, sulfur-containing and nitrogen-containing organic compounds. Oxidation feedstock is contacted with a soluble quaternary ammonium salt containing halogen, suflate, or bisulfate anion, and an immiscible aqueous phase comprising a source of hydrogen peroxide, and at least one member of the group consisting of phosphomolybdic acid and phosphotungstic acid, in a liquid reaction mixture under conditions suitable for reaction of one or more of the sulfur-containing and/or nitrogen-containing organic compounds. Blending components containing less sulfur and/or less nitrogen than the oxidation feedstock are recovered from the reaction mixture. Advantageously, at least a portion of the immiscible acid-containing phase is recycled to the oxidation.

44 citations


Journal ArticleDOI
TL;DR: In this paper, a photochromic nanocomposite thin film containing phosphotungstic acid entrapped in polyacrylamide was prepared using ultrasound technique and it was found that the thermal stability of the hybrid film was lower than that of pure polymer but the film was stable enough for photo chromic application from the TG-DTA curves.

44 citations


Journal ArticleDOI
TL;DR: In this article, the effect of catalysts on the acylation of anisole with α,β-unsaturated acids was investigated using phosphotungstic acid (H 3 PW 12 O 40 ), as pure form, supported on SiO 2 and in the form of cesium salts as catalysts.
Abstract: The mechanism of the acylation of anisole with α,β-unsaturated acids, i.e. acrylic, crotonic and methylcrotonic acid, has been investigated using phosphotungstic acid (H 3 PW 12 O 40 ), as pure form, supported on SiO 2 and in the form of cesium salts as catalysts. Since α,β-unsaturated acid can either alkylate and/or acylate the aromatic compound, the influence of the catalyst on the selectivity for these two competing reactions was studied. Analysis of products obtained on the acylation of aromatic compounds with α,β-unsaturated acids shows that all the catalysts are more active for acylation than alkylation. Secondary products coming from intermolecular reactions of the acylated product with anisole as well as tertiary products coming from its further decomposition and recombination with another anisole molecule were observed. Heteropolyacids supported on silica were found to be more active and selective towards acylation reactions than zeolites HY and Hβ, even when the activity per acid site was considered. Zeolites and cesium salts from heteropolyacids favor acid polymerization reaction rather than the acylation of the aromatic compound.

35 citations


Journal ArticleDOI
TL;DR: In this paper, the composites of heteropolyacid hydrates (PTA·nH2O and Phosphomolybdic acid : PMA·n H2O) with salt hydrate dispersoids (Aluminium sulphate and Ammonium paratungstate (APT) as dispersoids) have been studied and compared with composites PTA : Al 2O3 and PMA : Al2O3, and it has been found that the conductivity of 0.5PTA+0.5Al2(SO4)
Abstract: Proton conduction in the composites of heteropolyacid hydrates (Phosphotungstic acid : PTA·nH2O and Phosphomolybdic acid : PMA·nH2O) with salt hydrates like Aluminium sulphate and Ammonium paratungstate (APT) as dispersoids has been studied and compared with the composites PTA : Al2O3 and PMA : Al2O3. Thermal analysis, XRD and IR studies on acid and salt hydrates dispersed phase systems reveal the formation of composites. A significant increase in the ionic conductivity has been observed in the composites. It has been found that the conductivity of 0.5PTA + 0.5Al2(SO4)3·16H2O is ∼1.1 × 10−2 S·cm−1 and that of 0.55PMA + 0.45APT is ∼1.3 × 10−3 S·cm−1 at 65% R.H. The temperature and humidity dependence of bulk electrical conductivity of the composites is also reported.

16 citations


Journal ArticleDOI
TL;DR: In this paper, conversion of dimethyl ether and carbon monoxide to methyl acetate is investigated over a variety of group VIII metal-substituted phosphotungstic acid salts using rhodium, iridium, ruthenium, and palladium catalysts.
Abstract: Dimethyl ether (DME) can be produced much more efficiently in a single-stage, liquid-phase process from natural gas-based syngas as compared to the conventional process via dehydration of methanol This process, based on dual catalysts slurried in inert oil, alleviates the chemical equilibrium limitation governing the methanol synthesis reaction and concurrently improves per-pass syngas conversion and reactor productivity The potential, therefore, for production of methyl acetate via dimethyl ether carbonylation is of industrial importance In the present study, conversion of dimethyl ether and carbon monoxide to methyl acetate is investigated over a variety of group VIII metal-substituted phosphotungstic acid salts Experimental results of this catalytic reaction using rhodium, iridium, ruthenium, and palladium catalysts are evaluated and compared in terms of selectivity toward methyl acetate The effects of active metal, support types, multiple metal loading, and feed conditions on carbonylation activi

15 citations


Journal ArticleDOI
TL;DR: In this article, a thin-layer chromatographic analysis of trehalose content in sugar-rich products was successfully standardised using silica gel impregnated with phosphotungstic acid of pH 2.5, a solvent system of n -butanol: pyridine: water 8:4:3, and 6.5 mM N-(1-naphthyl)-ethylenediamine dihydrochloride in methanol, containing 3% H 2 SO 4 as the spraying agent.

14 citations


Journal ArticleDOI
TL;DR: In this paper, composites of Keggin heteropolymetalates have been prepared and characterized by SEM, XPS, 31 P-magic angle spinning/nuclear magnetic resonance and differential scanning calorimetry.
Abstract: Composites of Keggin heteropolymetalates have been prepared and characterized by SEM, XPS, 31 P-magic angle spinning/nuclear magnetic resonance and differential scanning calorimetry. The phosphotungstic acid and phosphomolybdic acid form nanocomposites where the oxocluster structure is preserved and is highly dispersed over the material, probably inserted between the polymeric chains. Phosphovanadotungstic clusters suffer partial decomposition during composite formation, resulting in a biphasic microcomposite. The decomposition product, phosphotungstic acid presents surface segregation as shown by comparison of XPS and nuclear magnetic resonance results.

10 citations


Li Lei1
01 Jan 2002
TL;DR: In this article, a proton conducting membrane composed of PWA and polyvinyl alcohol (PVA) was used to demonstrate that most of the acid embedded are stable in the PVA matrix when the membrane is immerged in water or methanol solution at room temperature.
Abstract: Proton conducting membranes composed of phosphotungstic acid (PWA) and poly (vinyl alcohol) (PVA) were prepared. Conductivity and Fourier transform infrared spectrometer(FTIR) measurements show that most of the acid embedded are stable in the PVA matrix when the membrane is immerged in water or methanol solution at room temperature. Conductivity of the composite membranes scatters around 10-3S cm-1 at room temperature. The methanol crossover through the membranes is about an order of magnitude lower than that through Nafion 117 membrane.

7 citations


Journal ArticleDOI
TL;DR: The presence of two maxima has been attributed to two different percolation thresholds for the two possible mobile protonic species H+ (H3O+) and OH- arising from the hydrates as mentioned in this paper.
Abstract: Proton conducting composites of heteropolyacid hydrates (phosphomolybdic acid H3PMo12O40.nH2O, PMA; phosphotungstic acid H3PW12O40.nH2O, PTA) and salt hydrate like NiCl2.6H2O were prepared with insulating Al2O3 as dispersoid. The ionic conductivity peaks at two concentrations of Al2O3 indicating two percolation thresholds for proton conduction. Two separate experiments were carried out to check the existence of such percolation thresholds viz. the volta battery experiment involving the measurement of e.m.f. of an electrochemical cell with composites of different compositions used as electrolyte and the composition vs conductivity measured by the complex impedance spectroscopy. The presence of two maxima has been attributed to two different percolation thresholds for the two possible mobile protonic species H+ (H3O+) and OH- arising from the hydrates.

4 citations


Journal ArticleDOI
01 Sep 2002
TL;DR: Stable, colloidal sols of submicron size were prepared by titration of aqueous solutions of alkylene oxide surfactants with phosphotungstic acid, H(3)PW(12)O(40) (PTA), followed by neutralization with ammonium or potassium hydroxide, and the stoichiometry of the complex was determined by (1)H and (31)P NMR.
Abstract: Stable, colloidal sols of submicron size were prepared by titration of aqueous solutions of alkylene oxide surfactants with phosphotungstic acid, H 3 PW 12 O 40 (PTA), followed by neutralization with ammonium or potassium hydroxide. The stoichiometry of the complex between phosphotungstic acid and the ethoxylated surfactant was determined by 1 H and 31 P NMR and was dependent upon the degree of ethoxylation. For example, in the ethoxylated octylphenol having 9–10 ethylene oxide units, Triton X-100, the mole ratio of surfactant to PTA was 4.5. In the ethoxylated octylphenol having 70 ethylene oxide units, Triton X-705, the mole ratio of surfactant to PTA was 1. Prior to nucleation of particles, phosphotungstic acid forms an apparent yellow charge transfer complex with ethoxylated alkylphenol surfactants, typified by Triton X-405. This complex is characterized by an absorption spectrum that is the sum of the spectra of Triton X-405 and PTA with a very weak shoulder at 400–500 nm. Particles were nearly monodisperse and their size was dependent on the nonionic surfactant employed, the heteropolyacid, and the rate of addition of heteropolyacid solution.

Patent
09 Oct 2002
TL;DR: In this paper, a process for catalytically synthesizing pentaerythritol tetraheptanoate is characterized by that the penta and heptanoic acid in a mole ratio of 1:(5-7) are used as raw materials and the phosphotungstic acid is used as catalyst.
Abstract: A process for catalytically synthesizing pentaerythritol tetraheptanoate is characterized by that the pentaerythritol and heptanoic acid in a mole ratio of 1:(5-7) are used as raw materials and the phosphotungstic acid is used as catalyst. Its advantages are high catalytic effect, high esterifying rate, short reaction time and low cost.

Patent
26 Jan 2002
TL;DR: In this paper, a method for dyeing cytoplasm using the composition is provided, to carry out the dyeing of cytopls by only one step, thereby reducing the amount of used reagents and the coloring time.
Abstract: PURPOSE: A cytoplasm dyeing composition and a method for dyeing cytoplasm using the composition are provided, to carry out the dyeing of cytoplasm by only one step, thereby reducing the amount of used reagents and the dyeing time. CONSTITUTION: The cytoplasm dyeing composition comprises 0.005-0.05 wt% of orange-G; 0.007-0.07 wt% of light green; 0.09-0.9 wt% of eosin Y; 0.08-0.9 wt% of phosphotungstic acid; 0.01-0.5 wt% of lithium carbonate; 0.3-0.7 wt% of distilled water; 90-95 wt% of an alcohol; and 0.3-0.7 wt% of an acid material. Preferably the alcohol is selected from the group consisting of methanol, ethanol, propanol and butanol; and the acidic material is selected from the group consisting of glacial acetic acid, HCl and formic acid. The pH of the dyeing composition is preferably 4-9.

Peng, Zhou, Xin, Ping, Wang, Tian, Xi, Cai 
01 Jan 2002
TL;DR: In this article, the PW12-H2SO4/SiO2 catalyst is used for vapor phase nitration of benzene to nitrobenzene (NB) using 65% nitric acid at normal pressure.
Abstract: Experimental results in this work demonstrate that PW12-H2SO4/SiO2 catalyst is a good and durable catalyst for vapor phase nitration of benzene to nitrobenzene (NB) using 65% nitric acid at normal pressure. It retains the advantages of using H2SO4 as catalyst and the addition of phosphotungstic acid holds back the effusion of sulfuric acid. This new catalyst keeps high activity (the conversion of HNO3 is more than 92%), high selectivity of NB (more than 97%) and high space time yield (STY 1.5 kg NB/kg cat.h) even after 150 h on stream, under condition of 423 K, SV=3200 ml/g h.