Showing papers on "Phosphotungstic acid published in 1998"
TL;DR: In this paper, the acidity and its effects on reactivity of Keggin-type heteropolycompounds were examined by catalytic probe reactions, microcalorimetry of ammonia sorption, and density functional quantum chemical calculations.
Abstract: The acidity and its effects on reactivity of Keggin-type heteropolycompounds were examined by catalytic probe reactions, microcalorimetry of ammonia sorption, and density functional quantum chemical calculations. Phosphotungstic, phosphomolybdic, silicotungstic, and silicomolybdic acids were used as model compounds. The specific rates of double-bond isomerization of both 1-butene and cis-2-butene were orders of magnitude greater on the tungsten heteropolyacids than on molybdenum heteropolyacids, which suggests the tungsten-containing solids are stronger acids. The rate of double-bond isomerization over silicotungstic acid was similar to that over phosphotungstic acid, indicating the minor role of the heteroatom. Results from ammonia sorption microcalorimetry showed ΔHsorp on tungsten-based heteropolyacids was approximately 40 kJ mol-1 higher than the corresponding enthalpy obtained on molybdenum-based heteropolyacids. Residual waters of hydration significantly affected both reaction rates and sorption ent...
166 citations
TL;DR: In this article, the influence of the catalyst on the selectivity for acylation and alkylation with crotonic acid has been studied, and it was shown that all the catalysts are more active for acylation than for alkylation.
Abstract: Pure phosphotungstic acid (H 3 PW 12 O 40 ), supported on SiO 2 and in the form of Cesium salts have been studied as acid catalysts for the acylation of toluene, p -xylene and m -xylene with crotonic acid. Since crotonic acid can either alkylate and/or acylate the alkylaromatic compounds, it was specifically selected to study the influence of the catalyst on the selectivity for these two competing reactions. Analysis of products obtained when acylating with an α , β -unsaturated acid show that all the catalysts are more active for acylation than for alkylation. Heteropolyacids were found to be more active than zeolites H-Y and Beta, even when the activity per acid site was considered. In the case of heteropolyacids, their activity is directly related to the number of accessible Bronsted acid sites.
58 citations
TL;DR: In this article, the authors investigated the effect of Triton X-114 on the internal structure of tetramethyl orthosilicate (TOMS) and showed that the results were consistent with recent reports on the templating of the internal structures of TPMS by macrosystems such as micelles.
39 citations
TL;DR: In this article, a tungsten oxide group of phosphotungstic acid with a Rh(II) acetate dimer yielded a species, Rh2POM, that catalyzed the electrochemical oxidation of L-methionine (L-Met), L-cystine, and As(III).
Abstract: Replacing a tungsten oxide group of phosphotungstic acid with a Rh(II) acetate dimer yielded a species, Rh2POM, that catalyzed the electrochemical oxidation of L-methionine (L-Met), L-cystine, and As(III) The electrocatalytic activity of Rh2POM was greater than that of the simple Rh(II) acetate dimer in homogeneous solution A conducting carbon-composite electrode (CCE) comprising Rh2POM and carbon powder in a silica matrix prepared by sol-gel chemistry was catalytically active over the pH range 2–10 The CCEs produced voltammetric responses toward L-Met and L-cystine that were pH independent over the above range and were stable for at least 4 months under dry storage If passivated, the catalytic activity was reproducibly generated by polishing For example, a relative standard deviation of 29 % (5 points) was obtained when the surface was polished between cyclic voltammetric experiments on 50 mM L-Met at pH 74 A least squares fit of flow injection amperometric data obtained over the range 5–156 μM L-Met (7 points) yielded the following: slope, 085 μA mM−1; intercept, 005 μA; and r / 0995 The detection limit was 23 μM
30 citations
TL;DR: TCA/PTA has the capacity to precipitate a wider cross-section of proteins than TCA alone, the combination of acids remaining effective in the presence of SDS and other detergents.
25 citations
TL;DR: In this article, an electrode-kinetic study of the oxidation of CO and CO/H2 mixtures on a Pt-Ru/C catalyst was carried out in phosphotungstic acid (PWA) electrolyte.
Abstract: An electrode-kinetic study of the oxidation of CO and CO/H2 mixtures on a Pt–Ru/C catalyst was carried out in phosphotungstic acid (PWA) electrolyte. The influence of temperature, CO partial pressure and proton concentration on the electrochemical oxidation rate was investigated. An apparent activation energy of about 50kJmol−1 was found for CO oxidation at 0.6V vs NHE. Fractional reaction orders close to 0.5 and −0.4 with respect to carbon monoxide and proton concentration, respectively, were observed. Tafel slopes were close to 136mVdec−1 at 70°C for both CO and CO/H2 oxidation. The PWA electrolyte appeared to promote the methanol electrooxidation by increasing the rate of water discharge at the electrode.
23 citations
TL;DR: In this article, an increase of platinum particle size was observed on both anodes and cathodes with the time of operation in a fuel cell and the uptake of electrolyte by the catalyst layers increased during cell operation.
19 citations
TL;DR: In this article, the formation of new states in the electronic structure of TiO2 and the PWA was monitored by XPS using a novel prepn. technique, and the coloration efficiency of the deposit was about 20 cm2/C.
16 citations
Patent•
01 Jun 1998
TL;DR: In this paper, the authors proposed a solution to improve water dispersibility and satisfy the effect of emulsion stabilization by setting a longitudinal size of a bar-like cellulose particle dispersed in water to a specified dimension.
Abstract: PROBLEM TO BE SOLVED: To improve water dispersibility and satisfy the effect of thickening, emulsion stabilization or the like in an aqueous solution by setting a longitudinal size of a bar-like cellulose particle dispersed in water to a specified dimension. SOLUTION: A longitudinal size of a cellulose particle is set to a dimension up to a maximum of 2 μm, preferably up to a maximum of 500 nm. Preferably, a longitudinal size of not less than 50% of the particles is set to a dimension of 0.01-100 mm or a longitudinal size of not less than 40% thereof is set to a dimension of 0.01-50 nm. The fine cellulose particle can be produced by hydrolyzing a cellulose (e.g. a conifer wood pulp) in an aqueous solution containing one or more inorganic acids, preferably selected from hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, phosphotungstic acid and phosphomolybdic acid. The concentration of an inorganic acid is preferably 0.01-12 mol/l and the hydrolysis is preferably carried out in an aqueous solution of an inorganic acid at a temperature of 10-110 deg.C for not less than 1 min.
6 citations
Patent•
07 Apr 1998
TL;DR: In this paper, a 2-30C olefin or its derivative is brought into contact with a partially or a completely neutralized heteropoly acid to afford a polymer having at least about 6 polyisobutylene having 300-20,000 Mn and the total content of the terminal vinylidene and the β-isomer (II) of the polymer is preferably at least 60%.
Abstract: PROBLEM TO BE SOLVED: To carry out the polymerization of an olefin at a high polymerization degree in a high yield by using a heteropoly acid or its derivative as a catalyst. SOLUTION: (A) A 2-30C olefin or its derivative is brought into contact with (B) a partially or a completely neutralized heteropoly acid to afford a polymer having at least about 6 polymerization degree. Furthermore, the component B is preferably phosphotungstic acid (especially Cs2.5 H0.5 PW12 O40 ), silicotungstic acid, phosphomolybdic acid or silicomolybdic acid and the component A is preferably isobutylene. The resultant polymer is preferably polyisobutylene having 300-20,000 Mn and the total content of the terminal vinylidene and the β-isomer (II) of the polymer is preferably at least 60%.
4 citations
TL;DR: In this article, a linear correlation was observed between protein selectivity and number of strong acid sites with strength of H 0≤−5.6.p-Xylene selectivity was evaluated as a function of x.
Abstract: Alkylation of toluene was carried out on microporous salts of phosphotungstic acid. Among the systems studied, M2.5H0.5PW12O40 showed maximum catalytic activity.p-Xylene selectivity was evaluated as a function of x. A linear correlation was observed betweenpara-selectivity and number of strong acid sites with strength of H0≤−5.6.
TL;DR: Alkylation of toluene with methanol was carried out on potassium, ammonium, cesium and thallium salts of phosphotungstic acid (M x H 3x PW 12 O 40 ; M=K +,NH4 +,Cs + and Tl +, x is varied from 0 to 3) as mentioned in this paper.
Abstract: Alkylation of toluene with methanol was carried out on potassium, ammonium, cesium and thallium salts of phosphotungstic acid (M x H 3x PW 12 O 40 ; M=K + ,NH4 + ,Cs + and Tl + , x is varied from 0 to 3). The major products obtained are xylenes, tri - and tetra-methylbenzenes. The selectivity of p-xylene was found to be higher than the equilibrium values. The salts with composition M 2.5 H 0.5 PW 12 O 40 showed maximum activity and para selectivity. p-Xylene selectivity was evaluated as a function of x. It is seen that para selectivity correlates linearly with the number of strong acid sites with a strength of H o ≤5.6.
TL;DR: In this paper, a linear correlation with a slope of 1.20±0.10 was observed between the distribution ratio of americium (DAm) with phosphotungstic acid concentration, suggesting the formation of 1:1 M:L species.
Abstract: Distribution studies of Am(III) and Eu(III) were carried out in an aqueous biphasic system consisting of (NH^SO« and polyethylene glycol (PEG) in presence of phosphotungstic acid (PTA) as the counter anion. A linear correlation with a slope of 1.20±0.10 was observed between the distribution ratio of americium (DAm) with phosphotungstic acid concentration, suggesting the formation of 1:1 M:L species. In the pH range 3.2 to 4.2, a linear plot of log D ^ vs. pH was obtained with a slope of 2.83 ±0.05 beyond which a plateau was seen. The extracting ability of the different PEGs employed in this work followed the trend: PEG-1000 > PEG-2000 > PEG-3400. Eu(III) was extracted to a much lower extent than Am(III). The separation factor values (0Am/Z)Eu) obtained were 15.4, 4.30 and 2.76 for PEG-1000, PEG-2000 and PEG-3400, respectively.
TL;DR: In this article, surface active cations (A+) in an aqueous medium, at pH 1.0 with excess phosphotungstic acid, form compounds with the composition A3[PW12O40], but at pH 4.5, they form acid salts AnH7−n[pW11O39]·xH2O that have a nanoperiodic structure.
Abstract: Surface-active cations (A+) in an aqueous medium, at pH 1.0 with excess phosphotungstic acid, form compounds with the composition A3[PW12O40]; but at pH 4.5, they form acid salts AnH7−n[PW11O39]·xH2O that have a nanoperiodic structure. The structural parameters are greatly dependent on the nature of the surfactant and on the type of heteropolyion.
Patent•
23 Dec 1998
TL;DR: Salicylic acid and propylene as material react at 80-120 deg.c temperature and 0.5-1.5 MPa pressure for 10-40 hr in the presence of catalyst including sulfuric acid and other liquid acid, superstrongacid, cation exchange resin and other solid acid and phosphotungstic acid as discussed by the authors.
Abstract: Salicylic acid and propylene as material react at 80-120 deg.c temperature and 0.5-1.5 MPa pressure for 10-40 hr in the presence of catalyst including sulfuric acid and other liquid acid, superstrongacid, cation exchange resin and other solid acid and phosphotungstic acid; and through cooling to room temperature, filtration to recover unreacted salicylic acid, neutralization with CaO or CaCO3 and filtration to eliminate residue, the product isopropyl salicylate as filtrate is obtained. The said process is one advanced technological process with once completed reaction, almost no side reaction, low material consumption, high transformation rare, low power consumption, low cost and high product quality.