Heteropoly Compounds

Lee, Kwan‐Young; Misono, Makoto

doi:10.1002/9783527610044.hetcat0018

Cited by 4 publications

(3 citation statements)

References 214 publications

(130 reference statements)

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“…Figure shows the XRD patterns of the different V 1 and V 2 heteropolyvanadates. The typical reflexion at 2θ = 9° is a typical feature of the Keggin structure. , Despite a usual decrease in stability while introducing a second V-atom in the Keggin unit, the relative intensity was kept elevated on the powder diffraction patterns for the materials obtained via the classical procedure . However, the materials prepared by the hydrothermal method exhibited a reduced crystallinity.…”

Section: Characterizations Of Pom Materialsmentioning

confidence: 99%

“…Because of their simple synthesis procedure and thermal stability, polyoxometalates (POM) having the Keggin structure are often used in acid catalysis. − These acid POMs are molecular clusters formed by different metal oxides with the general formula H 3 PM 12 O 40 . Heteropolyacids are ionic crystals in the solid state, consisting of large polyanions (primary structure: PM 12 O 40 3− ), counter cations, and water of crystallization.…”

Section: Introductionmentioning

confidence: 99%

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How Keggin-Type Polyoxometalates Self-Organize into Crystals

Esteves

Pereira

Arichi

et al. 2009

Crystal Growth & Design

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Vanadium-containing polyoxometalates (POM) were synthesized by two distinct procedures (hydrothermal and under acidic conditions) and were thoroughly characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer−Emmett−Teller (BET) method, UV−vis, 31P and 51V magic angle spinning NMR, scanning electron microscopy, and extended X-ray absorption fine structure spectroscopy-X-ray absorption near-edge spectroscopy (EXAFS-XANES). POM crystals were successfully grown under acidic atmosphere, thus forming a self-assembled structure constituted by cubic crystals that are between 20 and 80 μm in size. EXAFS-XANES experiments and molecular orbital calculations upon the Keggin unit cell allowed the determination of both the nature of the interactions and the assembly of the polyanions. A growth model was therefore developed based on the aggregation of Keggin units, ranging from one heteropolyanion unit to a crystal. Herein, we report a bottom-up approach which can serve as a powerful tool to assemble complex nanostructures via self-assembly, as well as to identify the building blocks present in solution during the assembly process. Finally, these auto-organized cubic vanadomolybdate crystals exhibit the highest catalytic activity and selectivity in the liquid phase partial oxidation of 2-methylnaphtalene into K3 vitamin.

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Section: Characterizations Of Pom Materialsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

How Keggin-Type Polyoxometalates Self-Organize into Crystals

Esteves

Pereira

Arichi

et al. 2009

Crystal Growth & Design

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“…Polyoxometalates have received great attention in catalysis due to their variety of applications, both in homogeneous and in heterogeneous systems. − Among them, the most studied are those displaying the well-known Keggin structure [XM 12 O 40 ] n − (X = P, Si, Al, ..., and M = W, Mo), probably because some of them are commercially available or easy to prepare and, from a more scientific point of view, they are the most stable thermally. Their applications can be divided in two groups depending on the nature of the M metal in the polyoxometalate.…”

Section: Introductionmentioning

confidence: 99%

Grafting Reaction of Platinum Organometallic Complexes on Silica-Supported or Unsupported Heteropolyacids

et al. 2011

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Silica-supported Keggin-type heteropolyacids react with platinum(II) complexes displaying a Pt-CH3 group, leading to the evolution of methane and the formation of an organometallic fragment grafted on the polyacid. This species has been characterized by various physicochemical methods such as microanalyses, infrared spectroscopy, solid-state 1D and 2D MAS NMR, and EXAFS. Molecular models were also prepared by reaction of the nonsupported anhydrous polyacid with the platinum(II) methyl complexes. These compounds were characterized in solution by multinuclear NMR (1H, 13C, 183W, and 195Pt) and in the solid state by X-ray diffraction on monocrystals. All data indicate that the interaction between the platinum complex and the polyoxometalate is weak and that this system is better expressed as an organometallic platinum salt of the supported heteropolyacid. This complex can be seen as one of the intermediates in the partial oxidation of methane to methanol, its synthesis being the reverse reaction of the methane activation.

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Chitosan: An Upgraded Polysaccharide Waste for Organocatalysis

2015

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Green chemistry, directed towards the sustainable adaptation of human activity, is part of our society. Catalysis and waste upgrading are central aspects of green chemistry. Bringing them together would afford efficient chemical processes from the point of view of sustainability. Chitosan is a polyglucosamine generated from chitin, an abundant polysaccharide recycled from industrial marine wastes. Organocatalysts show some advantages over metallocatalysts in that they do not involve non‐renewable rare metals. However, they have drawbacks such as the need for high loadings and difficulties of recovery. This microreview presents recent achievements in the field of organocatalytic reactions promoted by chitosan as a heterogeneous catalytic material. Various organic reactions are reported, in which chitosan is engaged either as an insoluble organocatalyst or as a support for organocatalysts, being easily recycled and reused. Influences on the reaction outcomes are discussed. Although most reactions produce achiral products, a few asymmetric ones have emerged, demonstrating the capacity of chitosan to transfer its stereochemical information.

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Heteropoly Compounds

Abstract: The sections in this article are Structure and Catalytic Properties Heteropolyacids: Acid Forms in the Solid State and in Solution K eggin‐Type HPAs W ells– D awson‐Type HPAs Salts of … Show more

Cited by 4 publications

References 214 publications

How Keggin-Type Polyoxometalates Self-Organize into Crystals

How Keggin-Type Polyoxometalates Self-Organize into Crystals

Grafting Reaction of Platinum Organometallic Complexes on Silica-Supported or Unsupported Heteropolyacids

Chitosan: An Upgraded Polysaccharide Waste for Organocatalysis

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