Showing papers on "Phosphotungstic acid published in 2013"

Conversion of Cellulose and Cellobiose into Sorbitol Catalyzed by Ruthenium Supported on a Polyoxometalate/Metal-Organic Framework Hybrid

Abstract: Cellulose and cellobiose were selectively converted into sorbitol over water-tolerant phosphotungstic acid (PTA)/metal- organic-framework-hybrid-supported ruthenium catalysts, Ru-PTA/MIL-100(Cr), under aqueous hydrogenation conditions. The goal was to investigate the relationship between the acid/metal balance of bifunctional catalysts Ru-PTA/MIL-100(Cr) and their performance in the catalytic conversion of cellulose and cellobiose into sugar alcohols. The control of the amount and strength of acid sites in the supported PTA/MIL-100(Cr) was achieved through the effective control of encapsulated-PTA loading in MIL-100(Cr). This design and preparation method led to an appropriately balanced Ru-PTA/MIL-100(Cr) in terms of Ru dispersion and hydrogenation capacity on the one hand, and acid site density of PTA/MIL-100(Cr) (responsible for acid-catalyzed hydrolysis) on the other hand. The ratio of acid site density to the number of Ru surface atoms (n(A)/n(Ru)) of Ru-PTA/MIL-100(Cr) was used to monitor the balance between hydrogenation and hydrolysis functions; the optimum balance between the two catalytic functions, that is, 8.84

Magnetic nanoparticle supported polyoxometalate: An efficient and reusable catalyst for solvent-free synthesis of α-aminophosphonates

Abstract: a b s t r a c t A new magnetically separable catalyst consisting of phosphotungstic acid (PTA) supported on imidaz- ole functionalized silica coated cobalt ferrite nanoparticles was prepared. The synthesized catalyst was characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The immobilized phosphotungstic acid was shown to be an efficient heterogeneous catalyst for the synthesis of -aminophosphonates under solvent-free conditions at room temperature. The catalyst is readily recovered by simple magnetic decantation and can be recycled several times with no significant loss of catalytic activity.

Superacid-doped polybenzimidazole-decorated carbon nanotubes: a novel high-performance proton exchange nanocomposite membrane

Abstract: Here we demonstrate design and electrochemical characterization of novel proton exchange membranes based on Nafion and superacid-doped polymer coated carbon nanotubes (CNTs). Polybenzimidazole-decorated CNT (PBI-CNT), a high-performance proton exchange nanostructure, was doped using phosphotungstic acid (PWA) as a super proton conductor. The engineered nanohybrid structure was shown to retain water molecules and provide high proton conduction at low humidity and elevated temperatures. The developed complex nanomaterial was then incorporated into the Nafion matrix to fabricate nanocomposite membranes. The acid–base interactions between imidazole groups of PBI and sulfonate groups of Nafion facilitate proton conductivity, especially at elevated temperatures. The improved characteristics of the membranes at the nanoscale result in enhanced fuel cell power generation capacity (386 mW cm−2) at elevated temperatures and low humidity (40% R.H.), which was found to be considerably higher than the commercial Nafion®117 membrane (73 mW cm−2).

Phosphotungstic acid anchored to amino-functionalized core-shell magnetic mesoporous silica microspheres: a magnetically recoverable nanocomposite with enhanced photocatalytic activity.

Abstract: H 3 PW 12 O 40 was successfully anchored to the surface of amino-functionalized Fe 3 O 4 @SiO 2 @meso-SiO 2 microspheres by means of chemical bonding to aminosilane groups, aiming to remove unwanted organic compounds from aqueous media. The resultant multifunctional microspheres were thoroughly characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, infrared spectroscopy, inductively coupled plasma, and N 2 adsorption–desorption. The as-prepared microspheres possess unique properties including high magnetization (46.8 emu g −1 ), large BET surface area (135 m 2 g −1 ), and highly open mesopores (∼5.0 nm), and H 3 PW 12 O 40 loading is calculated to be ∼16.8%; and as a result, the as-prepared microspheres exhibit enhanced performance in degrading dyes under UV irradiation compared with pure H 3 PW 12 O 40 . Additionally, the photocatalyst can be easily recycled using an external magnetic field without losing the photocatalytic activity.

Phosphomolybdic and phosphotungstic acids as efficient catalysts for the synthesis of bridged 1,2,4,5-tetraoxanes from β-diketones and hydrogen peroxide.

Abstract: Phosphomolybdic acid (PMA) and phosphotungstic acid (PTA) efficiently catalyze the addition of H2O2 to β-diketones to form bridged 1,2,4,5-tetraoxanes. These reactions are not accompanied by the formation of monocyclic peroxides containing hydroxy and hydroperoxide groups or polymeric peroxides. The use of these catalysts made it possible to obtain bridged tetraoxanes from easily oxidizable benzoylacetone derivatives and α-unsubstituted β-diketones. The syntheses are scaled up to ten grams. The resulting peroxides can be easily isolated from the reaction mixture by column chromatography. The yield of tetraoxanes depends on the structure of β-diketone and varies from 12 to 83%. NMR monitoring of two bridged 1,2,4,5-tetraoxanes synthesis was carried out.

Supramolecular Organization in Organic–Inorganic Heterogeneous Hybrid Catalysts Formed from Polyoxometalate and Poly(ampholyte) Polymer

Abstract: Hybridization of polyoxometalates (POMs) via the formation of an organic−inorganic association constitutes a new route to develop a heterogeneous POM catalyst with tunable functionality imparted through supramolecular assembly. Herein, we report on strategies to obtain tunable well-defined supramolecular architectures of an organic−inorganic heterogeneous hybrid catalyst formed by the association of a hydrophobically substituted polyampholyte copolymer (poly N, N-diallyl-N-hexylamine-alt-maleic acid) and phosphotungstic acid (H3PW12O40) POMs. The self-assembling property of the initial polyampholyte copolymer matrix is modulated by controlling the pH of the hybridization solution. When deposited on a mica surface, isolated, long and extended polymer chains are formed under basic conditions (pH 7.9), while globular or coiled structures are formed under acidic conditions (pH 2). The supramolecular assembly of the POM-polymer hybrid is found to be directed by the type and quantities of charges present on the polyampholyte copolymer, which themselves depend on the pH conditions. The hypothesis is that the Keggin type [PW12O40]3− anions, which have a size of ∼1 nm, electrostatically bind to the positive charge sites of the polymer backbone. The hybrid material stabilized at pH 5.3 consists of POM-decorated polymer chains. Statistical analysis of distances between pairs of POM entities show narrow density distributions, suggesting that POM entities are attached to the polymer chains with a high level of order. Conversely, under acidic conditions (pH 2), the hybrid shows the formation of a core− shell type of structure. The strategies reported here, to tune the supramolecular assembly of organic−inorganic hybrid materials, are highly valuable for the design and a more rational utilization of POM heterogeneous catalysts in several chemical transformations.

An Efficient Catalyst for the Conversion of Fructose into Methyl Levulinate

Abstract: The catalytic alcoholysis of fructose in methanol to methyl levulinate was performed by using phosphotungstic acid iron catalysts. The catalysts were characterized by powder X-ray diffraction, infrared spectroscopy, and X-ray fluorescence spectroscopy. The results showed that the exchanging of H+ with Fe3+ ions could modify the acidity of H3PW12O40 and introduce some Lewis acidity into the molecules. The highest yield of methyl levulinate was obtained over the Fe-HPW-1 catalyst. This catalyst showed 100 % fructose conversion with 73.7 % yield of methyl levulinate at 130 °C, 2 MPa for 2 h, and it could be reused at least five times without obvious loss of activity. The results suggest that the combination of Bronsted acidity with some Lewis acidity could effectively promote the conversion of fructose in methanol to methyl levulinate.

Selective hydrogenation of phenol and derivatives over an ionic liquid-like copolymer stabilized palladium catalyst in aqueous media

Abstract: A combination of “water soluble” palladium nanoparticles stabilized by an ionic liquid-like copolymer and phosphotungstic acid synergistically promotes selective hydrogenation of phenol to cyclohexanone. The nanocatalyst preparation and selective phenol hydrogenation are successfully combined into a one-pot process in this research. Conversion exceeding 99% was achieved with >99% selectivity under an atmospheric pressure of hydrogen in aqueous media. Moreover, even at room temperature, >99% conversion and >99% selectivity could still be obtained. The generality of the catalyst system for this reaction was demonstrated by selective hydrogenation of other hydroxylated aromatic compounds with similar performance.

Organically modified montmorillonite and chitosan–phosphotungstic acid complex nanocomposites as high performance membranes for fuel cell applications

Abstract: Nanocomposite membranes based on polyelectrolyte complex (PEC) of chitosan/phosphotungstic acid (PWA) and different types of montmorillonite (MMT) were prepared as alternative membranes to Nafion for direct methanol fuel cell (DMFC) applications. Fourier transform infrared spectroscopy (FTIR) revealed an electrostatically fixed PWA within the PEC membranes, which avoids a decrease in proton conductivity at practical condition. Various amounts of pristine as well as organically modified MMT (OMMT) (MMT: Cloisite Na, OMMT: Cloisite 15A, and Cloisite 30B) were introduced to the PEC membranes to decrease in methanol permeability and, thus, enhance efficiency and power density of the cells. X-ray diffraction patterns of the nanocomposite membranes proved that MMT (or OMMT) layers were exfoliated in the membranes at loading weights of lower than 3 wt.%. Moreover, the proton conductivity and the methanol permeability as well as the water uptake behavior of the manufactured nanocomposite membranes were studied. According to the selectivity parameter, ratio of proton conductivity to methanol permeability, the PEC/2 wt.% MMT 30B was identified as the optimum composition. The DMFC performance tests were carried out at 70 °C and 5 M methanol feed and the optimum membrane showed higher maximum power density as well as acceptable durability compared to Nafion 117. The obtained results indicated that owing to the relatively high selectivity and power density, the optimum nanocomposite membrane could be considered as a promising polyelectrolyte membrane (PEM) for DMFC applications.