Showing papers on "Phosphotungstic acid published in 2003"

Aqueous Self-Assembly of Unsymmetric Peptide Bolaamphiphiles into Nanofibers with Hydrophilic Cores and Surfaces

Abstract: Unsymmetric peptide bolaamphiphiles that incorporate (l-glutamyl)3glycine at one terminus and either tetraethylene glycol or aspartic acid at the other were found to form hydrogels at low wt %, presumably by self-assembling into nanofibers presenting (l-glutamyl)3glycine at their surfaces and burying the second headgroup at their cores. Transmission electron microscopy measurements on 1 wt % gels negatively stained with phosphotungstic acid and positively stained with uranyl acetate show one-dimensional objects with diameters of 5 nm and lengths in excess of 1 μm. Circular dichroism and solid-state FTIR spectra indicate the adoption of β-sheet structure within the nanofibers.

A computational and experimental study of anhydrous phosphotungstic acid and its interaction with water molecules

Abstract: The hydration state of phosphotungstic acid (H 3 PW 12 O 40 ) was explored through the use of in situ Fourier transform infrared (FT-IR) spectroscopy, water sorption microcalorimetry, and density functional theory (DFT) quantum chemical calculations. In addition, the proton affinities of the various sites on the Keggin unit were evaluated. The small differences ( −1 ) between the proton affinities of bridge and terminal oxygen atoms indicate that protons likely reside on both types of sites on the Keggin unit. Vibrational spectra calculated by DFT and measured experimentally by in situ FT-IR spectroscopy compare very well. The adsorption energy of a water molecule on an anhydrous Keggin unit was calculated to be approximately −55 to −70 kJ mol −1 for the formation of H 3 O + , independent of protonic site. The range compares well to the heat of water sorption (−65 kJ mol −1 ) determined from microcalorimetry on a sample dehydrated at 573 K. The uptake of gaseous water molecules was found to be five times higher on a sample pretreated at 473 K than on one pretreated at 573 K, indicating that the hydrated secondary structure does not reform after the high temperature pretreatment. In situ FT-IR spectroscopy confirms the lack of reversibility during dehydration/rehydration treatment for samples heated to 573 K.

Anchored homogeneous catalysts: the role of the heteropoly acid anchoring agent

Abstract: Heteropoly acids (HPAs) are used to anchor catalytically active homogeneous complexes to supports by an interaction between the HPA and the metal atom of the complex. In an attempt to determine the nature of the HPA/metal bonding several substrates were hydrogenated using chiral and achiral complexes anchored to alumina by the commercially available Keggin HPAs, phosphotungstic acid (PTA), phosphomolybdic acid (PMA), silicotungstic acid (STA) and silicomolybdic acid (SMA). It was found that the nature of the HPA can have a significant influence on both the activity and selectivity of reactions run using these HPA anchored homogeneous catalysts. The results obtained indicate that there is a direct interaction between the HPA and the metal atom of the active organometallic complex. While these data do not unequivocally establish that there is a bond between the metal atom and an oxygen on the surface of the HPA, the extent to which the activity and selectivity change when different HPAs are used as anchors is more like what would be expected when one uses a series of ligands attached to the metal atom rather than changing the counterions associated with a charged organometallic species.

Beckmann rearrangement over phosphotungstic acid/SiMCM-41 cyclohexanone oxime to ε-caprolactam

Abstract: Vapor-phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam is reported for the first time on phosphotungstic acid (PWA)-supported SiMCM-41 catalyst. The catalyst was prepared in the laboratory following standard procedures and was characterised by XRD and FT-IR. By N2 adsorption, BET surface area, pore size and pore diameter were measured. The conversion of cyclohexanone oxime over the catalyst was studied in the temperature region of 250–400 °C using mainly acetonitrile as a solvent at different contact times. Increase in the reaction temperature to 325 °C enhances oxime conversion and the selectivity of e-caprolactam. An impressive catalytic performance of cyclohexanone oxime conversion >99% and e-caprolactam selectivity of 75% was observed on 30 wt.% PWA/SiMCM-41 at 325 °C using a feed containing10 wt.% oxime in acetonitrile at WHSV=3.24 h−1. The catalytic efficiency for this rearrangement reaction was studied, varying the PWA content from 10 to 50 wt.% on SiMCM-41 and also using benzene and ethanol as alternate solvents in place of acetonitrile. The rearrangement reaction and e-caprolactam selectivity with respect to catalyst physical characteristics, PWA content and type of solvent are discussed.

Cationic polymerization using heteropolyacid salt catalysts

Abstract: Acid catalysts are used in the production of several commercially important lubricant additives, including dispersants and antioxidants. While the use of conventional mineral and Lewis acids still dominate existing production, heterogeneous solid acid catalysts provide a future option for cost reduction and pollution prevention. The heteropolyacids discussed in this presentation are based on the parent phosphotungstic acid, H3PW12O40, which has been studied for many years as solid acid catalysts especially by Japanese researchers. A particular class of heterpolyacid salts of the formula (M+)2.5H0.5PW12O40 exhibit enhanced catalytic activity, which is believed to be due to the formation of a phase with nano-sized crystallites, as has been reported by Misono and coworkers. This class of heteropolyacid salts has been successfully applied by Lubrizol researchers to the production of high-reactivity polyisobutylene, a polymer used in the production of dispersants for commercial lubricants. Most notably, the catalyst of the formula (NH4+)2.5H0.5PW12O40 provides high conversion to the desired reactive vinylidene isomer and a unique polymer molecular weight distribution, which results in improved performance characteristics when compared to existing commercial AlCl3 and BF3 catalysts. Catalyst performance is effectively optimized by catalyst concentration in a slurry reactor, catalyst calcination temperature and loading on a silica support. This class of catalysts has also been successfully applied to a number of other acid-catalyzed processes for the production of additives, including for the antioxidant nonyl diphenylamine.

TiO2-Phosphotungstic Acid Photocatalysis Systems with an Energy Storage Ability

Abstract: Phosphotungstic acid (PWA) was utilized as the reductive energy storage substance instead of conventional WO, for the fabrication of an energy storage photocatalyst, which retains its reducing ability even after light irradiation. In the case where a PWA film was electrochemically charged at -0.8 V vs. Ag/AgCl for I h in 3 wt% aqueous NaCl, it showed longer self-discharge time than a WO 3 film of the same thickness. Photoelectrochemical properties of the PWA and WO 3 films coated with porous TiO 2 were also studied. The PWA and WO 3 films could be charged under UV light (1 mW/cm 2 ) for I h in 3 wt% aqueous NaCl. Although the amount of charge accumulated in the PWA-TiO 2 film was smaller than that in the WO 3 -TiO 2 film, the self-discharge time of the former was longer. Slower self-discharging process by O 2 , which may be advantageous for some applications, of the former is responsible for these results. The PWA-TiO 2 film showed relatively good durability after several cycles.

Ca2+-Keggin anion colloidal particles as templates for the growth of star-shaped calcite crystal assemblies

Abstract: The formation of star-shaped CaCO3 crystals by reaction of an aqueous solution of phosphotungstic acid and Ca2+ ions with CO2 is described. The phosphotungstate ions [(PW12O40)3- Keggin ions] complex with the Ca2+ ions in solution leading to the formation of highly uniform nanometer-sized colloidal particles of the salt, calcium phosphotungstate. Reaction of these nearly spherical colloidal particles with CO2 results in the growth of calcite with very regular, star-shaped morphology. Energy dispersive analysis of X-rays of the star-shaped calcite particles indicated the presence of the Keggin ions in the crystals suggesting that they play the role of nanoprecursors in the growth of calcite crystals with such unique morphology.

Photochromic behavior of nanocomposite hybrid films of finely dispersed phosphotungstic acid particles into polyacrylamide

Abstract: A series of nanocomposite hybrid films consisting of phosphotungstic acid (PW12) and polyacrylamide (PAM) were prepared. TEM images showed that PW12 particles with average diameter of tens of nanometer were finely dispersed in the film. FT-IR results suggested that the Keggin geometry of PW12 was still preserved inside the matrix and a charge-transfer bridge was built between PW12 and PAM through hydrogen bonds. Under UV irradiation, PW12 was reduced photochemically to yield various mixed-valency colored species (“heteropoly blues” or “heteropoly browns”). The extent of photoreduction was concerned with the concentration of PW12 and irradiation time. The presence and diffusion of oxygen played an important role in reversibility of photochromism.

Hydrolysis method of esters

Abstract: The ester hydrolyzing method includes hydrolyzing ester in water to produce C1-C10 fatty acid or aromatic acid and C1-C4 fatty alcohol under the presence of ammonium salt of heteropoly acid as catalyst. The ammonium salt of heteropoly acid is obtained through the reaction between heteropoly acid in Keggin structure and inorganic ammonium salt or organic amine, the heteropoly acid is selected from phosphotungstic acid, silicotungstic acid, silicomolybdic acid and phosphomolybdic acid; the inorganic ammonium salt is selected from ammonium carbonate, ammonium nitrate, ammonium sulfate, ammonium phosphate and diammonium hydrochloride; and the organic amine is selected from fatty amine, alicyclic amine and arylamine. The said ester hydrolyzing method can obtain high conversion rate in relatively lower water/ester ratio and relatively short time, and the catalyst is cheap and easy to separate from the product.

Novel SBA-15 supported heteropoly acid catalysts for benzene alkylation with 1-dodecene

Abstract: Phosphotungstic acid (PW) catalysts supported on the mesoporous molecular sieve SBA-15 have been prepared, characterized and evaluated in the alkylation reaction of benzene with 1-dodecene SBA-15 supported PW catalysts exhibit much higher catalytic activity, stability and selectivity compared with HY zeolite It is proposed that the high dispersion of PW on SBA-15, high surface area, mesoporosity and specific acidity of the catalyst could responsible for its catalytic performances

Silica Gel-Supported Phosphotungstic Acid (PTA) Catalysed Acylation of Alcohols and Phenols with Acetic Anhydride under Mild Reaction Conditions

Abstract: Phosphotungstic acid, which is commercially available, practically and efficiently catalyses the acylation of a series of alcohols and phenols with acetic anhydride at room temperature or at refluxing temperature.

Catalytic synthesis of acetals and ketals from pentaerythritol with carbonyl compounds over HPW/C

Abstract: Synthesis of ketals and acetals from 2,2bis(hydroxymethyl)propane1,3diol with aldehydes and ketones was catalysed by phosphotungstic acid supported on active carbon(HPW/C),and the factors influencing the yield were investigated.It is show that HPW/C was an excellent catalyst,and it was stabtilitive and reusable.The products were characterized by 1H NMR,IR and elemental analysis.

Catalyst for producing lower fatty acid ester and method for producing the same

Abstract: PROBLEM TO BE SOLVED: To obtain a catalyst for producing a lower fatty acid ester which has a high activity and also suppresses a side reaction and further has the catalytic activity that is not highly dependent on a physical property such as a specific surface area of a carrier. SOLUTION: This catalyst is a catalyst in which the indium salt of a heteropoly acid is carried by a carrier and which is used in producing the lower fatty acid ester from a lower fatty acid and a lower olefin. The heteropoly acid is examplified by a phosphotungstic acid, a silicotungstic acid, a phosphomolybdic acid, and a silicomolybdic acid. The carrier is examplified by silica, activated carbon, diatomite, alumina, silica-alumina, zeolite, titania, and zirconia. COPYRIGHT: (C)2003,JPO

Synthesis and electrochemical properties of mesostructured 12-phosphotungstic acid thin films with hierarchical structures by triblock copolymer templating

Abstract: Hexagonally mesostructured 12-phosphotungstic acid (PWA) thin films with both large pore size and hierarchical structures have been successfully prepared by using triblock copolymer templates for the first time. The films is composed by three kind of structures; PWA Keggin anion, monoclinic crystal structure consisting of PWA Keggin anion and organic part (hydrophilic component) of block copolymers, and the hexagonal mesostructure of self-arrayed PWA and block copolymers. The calcined PWA films show better electrochemical properties such as a faster faradic processes and larger specific capacity than normal P WA clusters.