17O NMR determination of proton sites in solid heteropoly acid H3PW12O40.31P,29Si and17O NMR, FT-IR and XRD study of H3PW12O40 and H4SiW12O40 supported on carbon

Kozhevnikov, I. V.; Sinnema, A.; Jansen, Reinier J.; Bekkum, H. van

doi:10.1007/bf00806992

Cited by 107 publications

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“…The 17 O and 23 Na NMR spectroscopic analyses provide evidence that 1 and 2 display an unusual behavior of strongly associating with their charge-balancing cations upon dissolution, and these results are described in the following [25][26][27][28] Angewandte Chemie discussions. In the solid state, the sodium atoms (16 per cluster) reside between the Keggin clusters, and each sodium atom bridges at least two separate Keggin ions.…”

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confidence: 91%

“…The surprising result of the 17 O solution experiments is the number of resolvable peaks in the spectral region of terminal and bridging oxygen atoms for 1 and 2 (see Table 1). Based on similar work on the related molybdates and tungstates, we expected to see only two peaks for the bridging oxygen atoms; [25][26][27][28] one for the m 2 -O bridging two edge-sharing NbO 6 octahedra and one for the m 2 -O bridging two corner-sharing NbO 6 octahedra. Yet we observe four signals.…”

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confidence: 98%

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[SiNb₁₂O₄₀]¹⁶⁻ and [GeNb₁₂O₄₀]¹⁶⁻: Highly Charged Keggin Ions with Sticky Surfaces

et al. 2004

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Heteropolyanions are negatively charged clusters of cornersharing and edge-sharing early transition-metal MO 6 octahedra and heteroatom XO 4 tetrahedra, in which the tetrahedra are usually located in the interior of the cluster.[1] The geometry, composition, and charge of these clusters are varied through synthesis parameters, and cluster properties are highly tunable as a function of these characteristics. Heteropolyanions have been employed in a range of applications that include virus-binding inorganic drugs, [2] homogeneous and heterogeneous catalysts, [3,4] electro-optic and electrochromic materials, [5,6] metal and protein binding, [7] and as building blocks for nanostructuring of materials.[8] The aKeggin geometry, which was first structurally characterized in 1933 by J. F. Keggin [9] for the phosphotungstic acid (H 3 PW 12 O 40 ) is one of the most widely recognized and thoroughly studied heteropolyanion geometries.[10] Following Keggin's initial discovery, solid-state and solution chemistries of the heteropolytungstates and heteropolymolybdates (i.e., H 4 SiMo 12 O 40 ) with the Keggin geometry have been well developed. These Keggin ions have been synthesized with a variety of atoms in the XO 4 tetrahedral site, numerous addenda atom substitutions in the MO 6 octahedral sites, as acids, and as salt compounds with a range of counter cations. [11,12] Given the apparent ubiquity of the Keggin geometry, it is not surprising that the first-observed heteropolyniobate (reported Nyman et al. in 2002 [13] ) was a Keggin ion. However, we first identified [13] O 2 are chemically quite different from the related heteropolymolybdate and heteropolytungstate Keggin ions in their synthetic approach, their pH stability, and their charge. The Nb Keggin ions are synthesized and stable in basic solutions (pH 7-12.5) and decompose in acidic solutions, whereas the Mo and W Keggin ions are synthesized and stable in acidic solutions (pH % 1-3) and decompose in more basic solutions. The Nb Keggin ions are synthesized hydrothermally at 190 8C from amorphous, hydrous niobium oxide and alkoxides of germanium or silicon, whereas the Mo and W Keggin ions are generally precipitated at room temperature from tungstic or molybdic acid or alkali precursors. Use of sodium silicate or sodium germanate as precursors rather than the alkoxides results in mixtures that contain the heteropolyniobate only as a minor phase, with poorly crystalline sodium niobates [14] as the major phase. The general differences between synthesis of heteropolyniobates and synthesis of heteropolymolybdates and heteropolytungstates have been discussed in detail previously. [13] The hydrothermal formation of Na 16

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[SiNb₁₂O₄₀]¹⁶⁻ and [GeNb₁₂O₄₀]¹⁶⁻: Highly Charged Keggin Ions with Sticky Surfaces

et al. 2004

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“…It has been shown in many instances that their anionic character allows ion-pairing with charged surface sites or ion-exchange. A solid-state NMR study has shown that HPAs interact strongly with carbon [19]. The interaction of W-based HPAs and filamentous carbon has also been studied [20].…”

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confidence: 98%

Molybdenum Oxoanions as Dispersing Agents in the Preparation of Pd/C Catalysts for the Selective Oxidation of Glyoxal

et al. 2012

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“…18.75 g (0.09 mol) of tetraethoxysilane and 2.21 g (0.01 mol) of 3-amiopropyltriethoxy silane (KH550) were added successively to a stirred mixture of ethanol (41.00 g, 0.089 mol), distilled water (53.00 g, 2.94 mol) and n-dodecylamine (5.09 g, 0.027 mol) at room temperature. Immediately, the turbid solution became milky, and stirring was continued for 3 days.…”

Section: Introductionmentioning

confidence: 99%

“…To improve catalytic applications of HPA, it is dispersed on high surface area of carries such as silica, active carbon, molecular sieves, Al 2 O 3 and so on, which facilitates the increasing of active sites on the surface and enhances the catalytic activity [17][18][19][20][21]. Mesoporous molecular sieve MCM-41 with tailorable pore sizes and extremely high surface areas has attracted considerable attention in the field of catalysis, separation and adsorption [22].…”

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confidence: 99%

Heteropolyacids Anchored on Amino-Functionalized MCM-41 via Condensation as Reusable Catalysts for Esterification

Liu

Wang

2009

Catal Lett

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Amino-functionalized MCM-41 was synthesized via direct condensation, as well as post-grafting, using 3-aminopropyltrimethoxysilane as the functionalization agent. Keggin and Preyssler-structured heteropolyacids (HPAs) were anchored on the surface of amino-functionalized MCM-41 by chemically bonding to amino groups. HPAs directly supported on MCM-41 by impregnation were also prepared for comparison. These catalysts were characterized by Infra-red spectroscopy, X-ray diffraction, N 2 -adsorption, Hammett indicator and UV-Vis spectroscopy, and evaluated in esterification of n-butanol with acetic acid. HPAs anchored on amino-functionalized MCM-41 via condensation give very stable and substantially higher activity than the ones via grafting. In contrast, MCM-41 supported HPA catalysts prepared by direct impregnating lose their catalytic activities rapidly due to the leaching of HPA active sites. The catalyst activity is discussed in relation with physicochemical properties.

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17O NMR determination of proton sites in solid heteropoly acid H3PW12O40.31P,29Si and17O NMR, FT-IR and XRD study of H3PW12O40 and H4SiW12O40 supported on carbon

Cited by 107 publications

References 16 publications

[SiNb₁₂O₄₀]¹⁶⁻ and [GeNb₁₂O₄₀]¹⁶⁻: Highly Charged Keggin Ions with Sticky Surfaces

[SiNb₁₂O₄₀]¹⁶⁻ and [GeNb₁₂O₄₀]¹⁶⁻: Highly Charged Keggin Ions with Sticky Surfaces

Molybdenum Oxoanions as Dispersing Agents in the Preparation of Pd/C Catalysts for the Selective Oxidation of Glyoxal

Heteropolyacids Anchored on Amino-Functionalized MCM-41 via Condensation as Reusable Catalysts for Esterification

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17O NMR determination of proton sites in solid heteropoly acid H3PW12O40.31P,29Si and17O NMR, FT-IR and XRD study of H3PW12O40 and H4SiW12O40 supported on carbon

Cited by 107 publications

References 16 publications

[SiNb12O40]16− and [GeNb12O40]16−: Highly Charged Keggin Ions with Sticky Surfaces

[SiNb12O40]16− and [GeNb12O40]16−: Highly Charged Keggin Ions with Sticky Surfaces

Molybdenum Oxoanions as Dispersing Agents in the Preparation of Pd/C Catalysts for the Selective Oxidation of Glyoxal

Heteropolyacids Anchored on Amino-Functionalized MCM-41 via Condensation as Reusable Catalysts for Esterification

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[SiNb₁₂O₄₀]¹⁶⁻ and [GeNb₁₂O₄₀]¹⁶⁻: Highly Charged Keggin Ions with Sticky Surfaces

[SiNb₁₂O₄₀]¹⁶⁻ and [GeNb₁₂O₄₀]¹⁶⁻: Highly Charged Keggin Ions with Sticky Surfaces