Selective Liquid Phase Oxidations in the Presence of Supported Polyoxometalates

Hill, Craig L.; Kholdeeva, Oxana A.

doi:10.1002/9781118356760.ch6

Cited by 22 publications

(22 citation statements)

References 208 publications

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“…To confirm that PW11 is the active center, a new catalyst was prepared with the same cation: the Venturello complex TBA4H3[PW4O24] (TBA[PW4]). This type of compound has been identified as an intermediate active species in a variety of oxidation reactions formed from the reaction of Keggintype polyoxometalates with hydrogen peroxide [45][46][47][48][49]. The Venturello TBA[PW4] was characterized by FTIR-ATR and 31 P NMR and the results were in agreement with the previously reported data by Julião et al (Figures S1 and S2 in the ESI) [41,46].…”

Section: Desulfurization Of Model Dieselsupporting

confidence: 87%

Solvent-Free Desulfurization System to Produce Low-Sulfur Diesel Using Hybrid Monovacant Keggin-Type Catalyst

et al. 2020

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Two quaternary ammonium catalysts based on the monovacant polyoxotungstate ([PW11O39]7−, abbreviated as PW11) were prepared and characterized. The desulfurization performances of the PW11-based hybrids (of tetrabutylammonium and trimethyloctadecylammonium, abbreviated as TBA[PW11] and ODA[PW11], respectively), the corresponding potassium salt (K7PW11O39, abbreviated as KPW11) and the peroxo-compound (TBA-PO4[WO(O2)2], abbreviated as TBA[PW4]) were compared as catalysts for the oxidative desulfurization of a multicomponent model diesel (2000 ppm S). The oxidative desulfurization studies (ODS) were performed using solvent-free systems and aqueous H2O2 as oxidant. The nature of the cation in the PW11 catalyst showed to have an important influence on the catalytic performance. In fact, the PW11-hybrid catalysts showed higher catalytic efficiency than the peroxo-compound TBA[PW4], known as Venturello compound. TBA[PW11] revealed a remarkable desulfurization performance with 96.5% of sulfur compounds removed in the first 130 min. The reusability and stability of the catalyst were also investigated for ten consecutive ODS cycles without loss of activity. A treated clean diesel could be recovered without sulfur compounds by performing a final liquid/liquid extraction diesel/EtOH:H2O mixture (1:1) after the catalytic oxidative step.

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Section: Desulfurization Of Model Dieselsupporting

confidence: 87%

Solvent-Free Desulfurization System to Produce Low-Sulfur Diesel Using Hybrid Monovacant Keggin-Type Catalyst

et al. 2020

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“…Despite the remarkable progress in surface science, mechanistic studies in heterogeneous catalysis continue to be sophisticated because of difficulties in the registration and identification of active catalytic species. Owing to their evident structural analogy with metal oxide surfaces and the possibility of studying at the atomic level, polyoxometalates (POMs) have served as convenient molecular models for heterogeneous metal oxide catalysts, , including single-site ones. − Moreover, a unique combination of properties, such as thermodynamic stability to oxidation and resistance to hydrolysis, tunable solubility, acidity, and redox activity, made POMs the focus of a wide range of research areas. − Proust and co-workers suggested using Zr-containing Lindqvist-type polyoxotungstates as soluble analogues of heterogeneous zirconia-supported tungsten catalysts. , Some of us have found similarities in the catalytic performance of Zr-monosubstituted Keggin-type POMs and mesoporous zirconium silicates. , These model studies based on the Keggin Zr-POMs revealed that the presence of acid protons is vital for their activity. While (Bu 4 N) 9 [{PW 11 O 39 Zr} 2 (μ-OH)(μ-O)] comprising no acid protons reacted with neither H 2 O nor H 2 O 2 and showed minor catalytic activity in oxidations with H 2 O 2 , its protonated forms, (Bu 4 N) 8 [{PW 11 O 39 Zr(μ-OH)} 2 ] and (Bu 4 N) 7 H[{PW 11 O 39 Zr(μ-OH)} 2 ], revealed significant activity .…”

Section: Introductionmentioning

confidence: 99%

Activation of H₂O₂ over Zr(IV). Insights from Model Studies on Zr-Monosubstituted Lindqvist Tungstates

Maksimchuk¹,

Evtushok²,

Zalomaeva³

et al. 2021

ACS Catal.

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Zr-monosubstituted Lindqvist-type polyoxometalates (Zr-POMs), (Bu 4 N) 2 [W 5 O 18 Zr(H 2 O) 3 ] (1) and (Bu 4 N) 6 [{W 5 O 18 Zr(μ-OH)} 2 ] (2), have been employed as molecular models to unravel the mechanism of hydrogen peroxide activation over Zr(IV) sites. Compounds 1 and 2 are hydrolytically stable and catalyze the epoxidation of CC bonds in unfunctionalized alkenes and α,β-unsaturated ketones, as well as sulfoxidation of thioethers. Monomer 1 is more active than dimer 2. Acid additives greatly accelerate the oxygenation reactions and increase oxidant utilization efficiency up to >99%. Product distributions are indicative of a heterolytic oxygen transfer mechanism that involves electrophilic oxidizing species formed upon the interaction of Zr-POM and H 2 O 2 . The interaction of 1 and 2 with H 2 O 2 and the resulting peroxo derivatives have been investigated by UV−vis, FTIR, Raman spectroscopy, HR-ESI-MS, and combined HPLC-ICPatomic emission spectroscopy techniques. The interaction between an 17 O-enriched dimer, (Bu 4 N) 6 [{W 5 O 18 Zr(μ-OCH 3 )} 2 ] (2′), and H 2 O 2 was also analyzed by 17 O NMR spectroscopy. Combining these experimental studies with DFT calculations suggested the existence of dimeric peroxo species [(μ-η 2 :η 2 -O 2 ){ZrW 5 O 18 } 2 ] 6− as well as monomeric Zr-hydroperoxo [W 5 O 18 Zr(η 2 -OOH)] 3− and Zr-peroxo [HW 5 O 18 Zr(η 2 - O 2 )] 3− species. Reactivity studies revealed that the dimeric peroxo is inert toward alkenes but is able to transfer oxygen atoms to thioethers, while the monomeric peroxo intermediate is capable of epoxidizing CC bonds. DFT analysis of the reaction mechanism identifies the monomeric Zr-hydroperoxo intermediate as the real epoxidizing species and the corresponding α-oxygen transfer to the substrate as the rate-determining step. The calculations also showed that protonation of Zr-POM significantly reduces the free-energy barrier of the key oxygen-transfer step because of the greater electrophilicity of the catalyst and that dimeric species hampers the approach of alkene substrates due to steric repulsions reducing its reactivity. The improved performance of the Zr(IV) catalyst relative to Ti(IV) and Nb(V) catalysts is respectively due to a flexible coordination environment and a low tendency to form energy deep-well and low-reactive Zr-peroxo intermediates.

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“…The relative ease of incorporating POMs into heterogeneous matrices is another reason they are particularly well-suited for construction of functional materials. Several strategies exist for the immobilization of POMs including electrostatic attraction, solvophobic interactions, or covalent linkages (Proust et al, 2012 ; Hill and Kholdeeva, 2013 ; Xiao et al, 2016 ). Immobilization of POMs through electrostatic and solvophobic interactions is the most common and simple method, owing to the high negative charge of the POMs and ease of counter cation exchange (to produce insoluble salts)(Proust et al, 2012 ).…”

Section: Pom Properties That Make Them Effective In Materials Applicamentioning

confidence: 99%

Multi-Tasking POM Systems

et al. 2018

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Polyoxometalate (POM)-based materials of current interest are summarized, and specific types of POM-containing systems are described in which material facilitates multiple complex interactions or catalytic processes. We specifically highlight POM-containing multi-hydrogen-bonding polymers that form gels upon exposure to select organic liquids and simultaneously catalyze hydrolytic or oxidative decontamination, as well as water oxidation catalysts (WOCs) that can be interfaced with light-absorbing photoelectrode materials for photoelectrocatalytic water splitting.

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Selective Liquid Phase Oxidations in the Presence of Supported Polyoxometalates

Cited by 22 publications

References 208 publications

Solvent-Free Desulfurization System to Produce Low-Sulfur Diesel Using Hybrid Monovacant Keggin-Type Catalyst

Solvent-Free Desulfurization System to Produce Low-Sulfur Diesel Using Hybrid Monovacant Keggin-Type Catalyst

Activation of H₂O₂ over Zr(IV). Insights from Model Studies on Zr-Monosubstituted Lindqvist Tungstates

Multi-Tasking POM Systems

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Selective Liquid Phase Oxidations in the Presence of Supported Polyoxometalates

Cited by 22 publications

References 208 publications

Solvent-Free Desulfurization System to Produce Low-Sulfur Diesel Using Hybrid Monovacant Keggin-Type Catalyst

Solvent-Free Desulfurization System to Produce Low-Sulfur Diesel Using Hybrid Monovacant Keggin-Type Catalyst

Activation of H2O2 over Zr(IV). Insights from Model Studies on Zr-Monosubstituted Lindqvist Tungstates

Multi-Tasking POM Systems

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Activation of H₂O₂ over Zr(IV). Insights from Model Studies on Zr-Monosubstituted Lindqvist Tungstates