Showing papers on "Phosphotungstic acid published in 1993"

Supported heteropoly acid catalysts for isoparaffin-olefin alkylation reactions

Abstract: The alkylation of isoparaffin with olefin to provide alkylate is carried out in the presence of, as catalyst, a supported heteropoly acid. The support may be MCM-41, and the heteropoly acid may be dodecawolframophosphoric acid (i.e., phosphotungstic acid, i.e., H 3 PW 12 O 40 ).

Use of tannic acid and silver enhancer to improve staining for electron microscopy and immunogold labeling.

Abstract: Staining by uranyl acetate and lead citrate (UA-LC) of immunolabeled sections of unfixed glomerular basement membrane (GBM) digests embedded in low-acid glycol methacrylate (LA-GMA) is poor. The following were investigated for their ability to enhance contrast when applied to sections before UA-LC: potassium permanganate, phosphotungstic acid, gold chloride, osmium tetroxide, glutaraldehyde-osmium tetroxide, colloidal gold-silver enhancer, tannic acid, and glutaraldehyde-tannic acid. Silver enhancer (2 min incubation, no sodium thiosulfate step) gave dense GBM staining but not with immunogold labeling. Silver enhancer is recommended as a simple alternative to routine silver stains but not for contrast enhancement with immunogold labeling. Tannic acid (1% for 1 min or 0.005% for 10 sec) and glutaraldehyde (2.5% for 5 min) followed by tannic acid enhanced contrast and, when applied after immunolabeling, did not appear to affect probe levels. Tannic acid also enhanced the staining of fixed tissue in LR Gold ...

New Oxidations of Organic Substrates Using Hydrogen Peroxide and Supported Heteropolyacid Catalysts

Abstract: Oxidation processes employing aqueous hydrogen peroxide in the presence of heterogeneous catalysts offer significant advantages over traditional liquid-phase processes in terms of cost, safety and environmental impact. We have previously shown1 that catalysts prepared by depositing phosphotungstic acid on gamma-alumina, followed by calcination, are active for the selective epoxidation of olefins using 35% H2O2. These catalysts have been demonstrated conclusively to operate heterogeneously, with essentially no observable leaching of tungsten into the reaction solvent (aqueous t-butanol). They may also be recycled many times without significant loss of activity. Best results are obtained with cyclic alkenes, there being no detectable steric limitations on the substrates which can react.

Production of carboxylic acid butyl ester

Abstract: PURPOSE:To provide an extremely effective process for producing a carboxylic acid butyl ester from a carboxylic acid and ethylene in one step in a good yield. CONSTITUTION:A process for producing a carboxylic acid butyl ester by reacting ethylene with a carboxylic acid in one step comprises employing a heteropolyacid produced by substituting with palladium cations a part of protons contained in the heteropolyacid consisting mainly of a tungsten oxide represented by phosphotungstic acid or silicotungstic acid as a catalyst. Therein, when the content of the crystal water contained in the heteropolyacid in which a part of the protons is substituted with the palladium cations is to <=3.0 molecules per molecule of the heteropolyacid, an extremely active catalyst is obtained.

Oxygen Reduction Kinetics in Phosphotungstic Acid at Low Temperature.

Abstract: The kinetics of O2 reduction reaction on Pt in concentrated phosphotungstic acid, H3PW12O40, has been investigated at low temperatures by using the microelectrode technique. Accordingly, the exchange current density, the oxygen solubility, the diffusion coefficient and the corresponding activation parameters have been determined. H3PW12O40 manifests promising characteristics for the oxygen electroreduction process especially in terms of oxygen solubility (5.03 × 10−6 mol cm−3 at 25°C) and H+ concentration (pK1 = 4.77 in HOAc) which account for high exchange current density values (8.63 × 10−8 A cm−2 and 6.06 × 10−7 A cm−2 at 25 and 60°C, respectively). A one electron process has been singled out as the rate limiting step for the oxygen reduction, suggesting that this reaction occurs on Pt under Langmuir conditions in phosphotungstic acid. The results are compared with those reported in the literature for concentrated H3PO4 and TFMSA solutions.

Production of potassium phosphotungstate

Abstract: PURPOSE:To advantageously produce potassium phosphotungstate capable of exhibiting high activity as an alkylating catalyst for aromatic compounds by bringing an aqueous solution of phosphotungstic acid into contact with solid potassium carbonate. CONSTITUTION:Solid potassium carbonate is added to an aqueous solution of phosphotungstic acid and both are brought into contact by stirring. In the process, the aforementioned aqueous solution preferably contains about 10-150g/100cc H3PW12O40. The aforementioned contact is preferably carried out at about 5-50 deg.C. The resultant formed precipitates are then concentrated under reduced pressure to afford the objective potassium phosphotungstate composed of HXK3-XPW12O40 (X is about 0.5-2.8). The obtained potassium phosphotungstate is subsequently used as a catalyst in alkylating aromatic compounds such as naphthalenes with an alkylating agent such as ethylene. The aforementioned potassium phosphotungstate is used in an amount of preferably about 0.0001-1 pt.wt. based on 1 pt.wt. aromatic compounds.

Production process for ethyl acetate

Abstract: PURPOSE:To provide a vapor-phase production process for industrially useful ethyl acetate through highly stabilized operations in high efficiency by using a heterogeneous catalyst. CONSTITUTION:Using a solid catalyst of phosphotungstic acid of which a part of the protons are replaced with cesium cation, the catalytic reaction between ethylene and acetic acid are carried out in vapor phase to produce ethyl acetate. The heterogeneous catalyst has extremely high reaction activity and high durability and excellent reaction selectivity, thus ethyl acetate can be produced very economically with high industrial advantage.