Applications of Polyoxometalates in Homogeneous Catalysis

Neumann, Roni

doi:10.1002/chin.200412231

Cited by 2 publications

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“…The general interest in polyoxometalate (POM) nanometric ions has spawned from their wide variety of compositions and structural versatility. − The presence of transition-metal atoms in a high oxidation state confer to POMs an extensive range of chemical and physical properties such as catalytic, − redox, , magnetic, dielectric, photoluminescence, and photochromic. − These many features allow POMs to be used in a wide range of applications such as chemical synthesis, materials science, electrochemistry, and medicine. ,− As surface effects are essential for most of the POM applications (e.g., ref ), numerous investigations have focused on their adsorption on soft or solid supports or via (hybrid) self-assembly. − …”

Section: Introductionmentioning

confidence: 99%

Are Keggin’s POMs Charged Nanocolloids or Multicharged Anions?

et al. 2018

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Owing to their multiple charges and their nanometric size, polyoxometalates (POMs) are at the frontier between ions and charged colloids. We investigated here the effect of POM-POM electrostatics repulsions on their self-diffusion in water by varying POM and supporting salt concentrations. The self-diffusion coefficients of two Keggin's POMs [silicotungstate (SiWO) and phosphotungstate (PWO)] were determined by dynamic light scattering (DLS) and H/P DOSY NMR, whereas POM-POM electrostatic repulsions were investigated by the determination of the static structure factors using small-angle X-ray scattering (SAXS). The self-diffusion coefficients for the two POMs and for different POM/background salt concentrations were collected in a master curve by comparing the averaged POM-POM distance in solution to the Debye length. As for classical charged colloids, we show that the POM's counterions should not be considered in the calculation of the ionic strength that governs POM-POM electrostatic repulsions. This result was confirmed by fitting the POM-POM structure factor by considering a pair potential of spherical charged particles using the well-known Hayter mean spherical approximation (MSA). These Keggin POMs also behave as (super)chaotropic anions (i.e., they have a strong propensity to adsorb on (neutral polar) surfaces, which was also investigated) here on the surface of octyl-β-glucoside (CG) micelles. The variations of (i) the chemical shift of H/P NMR signals and (ii) the self-diffusion coefficients obtained by DOSY H/P NMR of PW and of CG were in good agreement, confirming the strong adsorption of POMs on the micelle polar surface from static and dynamic points of view. We concluded that Keggin's POMs behave (i) as anions because they adsorb on surfaces as chaotropic anions and (ii) as colloids because they can be described by a classical colloidal approach by dynamic and static scattering techniques (i.e., by the investigation of their interparticle electrostatic structure factor and self-diffusion without considering the POM's counterions in the ionic strength calculation). This work highlights the dynamic properties of POMs at soft interfaces compared to bulk aqueous solution, which is essential in the understanding of functional properties of POMs, such as (photo)catalysis and the rational design of POM-based hybrid nanomaterials from soft templating routes (i.e., in aqueous solutions at room temperature).

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Section: Introductionmentioning

confidence: 99%

Are Keggin’s POMs Charged Nanocolloids or Multicharged Anions?

et al. 2018

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“…[4,8,[14][15][16][17][18][19][20][21][22][23][24] POMs possess several properties that make them ideal oxidation catalysts, for example, superior oxidative stability, rich redox chemistry, and tunable composition at the molecular level. [25] POMs can be used as both homogeneous and heterogeneous oxidation catalysts. [26][27][28][29][30][31] In general, heterogeneous catalytic processes are preferred, as they allow easier catalyst recovery and recycling, which is of significant industrial interest.…”

Section: Introductionmentioning

confidence: 99%

“…Among the various types of catalysts studied, polyoxometalates (POMs) are effective when used in combination with H 2 O 2 , , . POMs possess several properties that make them ideal oxidation catalysts, for example, superior oxidative stability, rich redox chemistry, and tunable composition at the molecular level …”

Section: Introductionmentioning

confidence: 99%

Zinc‐Substituted Polyoxotungstate@amino‐MIL‐101(Al) – An Efficient Catalyst for the Sustainable Desulfurization of Model and Real Diesels

et al. 2016

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The zinc‐substituted polyoxotungstate [PW11Zn(H2O)O39]5– (PW11Zn) has been encapsulated within the aluminium(III) 2‐aminoterephthalate NH2‐MIL‐101(Al) metal–organic framework (MOF) either directly through a one‐pot microwave‐assisted synthesis or by an impregnation method. The resultant composite materials were characterized by elemental analysis, powder X‐ray diffraction, FTIR spectroscopy, and 31P magic‐angle spinning (MAS) NMR spectroscopy. The desulfurization of a model diesel containing three refractory organosulfur compounds (1‐benzothiophene, dibenzothiophene, and 4,6‐dimethyldibenzothiophene) was studied with the ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate as an extractant, the PW11Zn@MOF composites as sulfoxidation catalysts, and aqueous H2O2 as an oxidant. The composite obtained by direct synthesis was the most efficient catalyst and led to almost complete desulfurization of the model diesel under mild conditions. Moreover, the solid catalyst could be recovered readily and recycled without significant loss of desulfurization performance. The application of this system to the treatment of a real diesel sample provided a very good sulfur removal of 83 % when combined with liquid–liquid extraction.

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Applications of Polyoxometalates in Homogeneous Catalysis

Cited by 2 publications

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Are Keggin’s POMs Charged Nanocolloids or Multicharged Anions?

Are Keggin’s POMs Charged Nanocolloids or Multicharged Anions?

Zinc‐Substituted Polyoxotungstate@amino‐MIL‐101(Al) – An Efficient Catalyst for the Sustainable Desulfurization of Model and Real Diesels

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