Raman studies on species in aqueous solutions. Part III. Vanadates, molybdates, and tungstates

Griffith, William P.; Leśniak, Piotr

doi:10.1039/j19690001066

Cited by 186 publications

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“…x AHM (0.01M) + y AMV (0.01M) + z AMW (0.01M) y = 0-30% z = 0-20% drying (30°C, vacuum) Activation: a. inert gas < 823K b. reaction mixture > 520K NH 4 …”

Section: Introductionmentioning

confidence: 99%

In situ Raman spectroscopy for the characterization of MoVW mixed oxide catalysts

Mestl

2002

J Raman Spectroscopy

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In situ Raman spectroscopy was used to characterize the synthesis and activation steps of mixed metal oxide catalysts starting from the mixed solutions, through subsequent drying and activation procedures, to the catalytic propene partial oxidation reaction. Comparison with Raman spectra recorded for defined, well-crystallized reference oxides allowed the assignment of the spectra obtained during the catalyst preparation to certain oxides, such as Mo 5 O 14 . Especially the latter oxide phase is relevant for selective partial oxidation catalysis. The selectivity for partial oxidation products could be improved between two-and three-fold when the amount of Mo 5 O 14 -type oxide increased. This phase forms from mixtures of molybdenum and tungsten and from mixtures of molybdenum, tungsten and vanadium, but not from binary mixtures of molybdenum and vanadium with high vanadium concentrations. Tungsten and vanadium play an important role as structural promoters in the formation and stabilization of this oxide and for high catalytic activity. A resonance Raman effect was proved for reduced molybdenum oxides due to resonant coupling of the exciting laser to the IVCT transitions between fivefold-coordinated Mo 5+ and sixfold-coordinated Mo 6+ . This resonance enhancement renders possible the in situ characterization of operating, reduced molybdenum oxide catalysts. In contrast to the Mo 5 O 14 -type phase, MoO 3−x exhibits a high selectivity to total oxidation, and it even becomes re-oxidized during propene partial oxidation. These different catalytic properties of MoO 3−x and the Mo 5 O 14 -type oxide led to the development of a structure-activity relationship which explains the behavior of industrial catalysts. A model is proposed on the basis of a bond order-Raman wavenumber relationship, which explains the different selectivities of these two oxides in terms of metal-oxygen bond strengths, i.e. oxygen basicity and oxygen lability, respectively.

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“…x AHM (0.01M) + y AMV (0.01M) + z AMW (0.01M) y = 0-30% z = 0-20% drying (30°C, vacuum) Activation: a. inert gas < 823K b. reaction mixture > 520K NH 4 …”

Section: Introductionmentioning

confidence: 99%

In situ Raman spectroscopy for the characterization of MoVW mixed oxide catalysts

Mestl

2002

J Raman Spectroscopy

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“…Several potentiometric (6,7) and spectrophotometric measurements (20)(21)(22)(23)(24) that were conducted at low solute concentration have led to the conclusion that the metavanadate ion is present in solution as the trimer "V30,3-" in the pH range of 9.0 to 7.0, while cryoscopic (1) and diffusion coefficient calculations (4) support the existence of the tetramer, "V4OlZ4-". Recent Raman data (15)(16)(17) suggested the presence of a cyclic polymer, but failed to show whether this polymer is a trimer or atetramer. Also, recent depolarized light scattering results (10) can be best explained if based on the presence of a tetramer.…”

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confidence: 99%

“…Vanadium(V) speciation in aqueous solutions has been studied in detail (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). A variety of techniques -ranging from salt cryoscopy (1, 3) and I diffusion coefficient measurements (4,5) to potentiometric (6,7), light scattering (9-lo), S'V-nmr (11)(12)(13)(14), Raman spectroscopy (15)(16)(17), and spectrochemical measurements (20)(21)(22)(23)(24), have been utilized.…”

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confidence: 99%

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⁵¹V FT-nmr investigations of metavanadate ions in aqueous solutions

Habayeb¹,

Hileman²

1980

Can. J. Chem.

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51V-nmr chemical shifts, line widths, and area ratios obtained for various vanadium(V) species in aqueous solutions as a function of counter ion, pH, and analytical vanadium concentration changes are reported. From these data the eight vanadium(V) species shown to be present in significant amounts are identified. In the pH range 8.5 to 7.0, 51V-nmr resonances were observed at 574 ppm and 582 ppm. The 574 ppm resonance is assigned to both V3O93− and V4O124− while the 582 ppm resonance has been assigned to the V6O174− species. The suggestion that tetra alkyl ammonium cations stabilize V4O124− species in solution is confirmed.

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“…Carbon (coke) deposition on the surface of catalyst is the main reason of catalyst deactivation; but it is also postulated that, at high pressure, carbon monoxide reacts with the transition metal, such as cobalt of the catalyst to form volatile carbonyl compounds, such as Co 2 (CO) 8 or HCo(CO) 4 which may leave the reactor with other products. In the Co-Mo catalyst, the transition metals are most likely bonded together through Co-Mo bonds, besides being bonded with remaining oxygen in the Co 2 Mo 7 metal clusters.…”

Section: Nova Journal Of Engineering and Applied Sciences Page: 4 Co mentioning

confidence: 99%

Hydrogenation of Carbon Monoxide and Carbon Dioxide over Nano γ-Alumina Supported Cobalt (III)/Molybdenum Catalyst

Takassi

Helalizadeh

Rad

2016

Nova J Eng Appl Sci

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Ligated dicobalt (III) heptamolybdate (CoL 6 ) 2 (Mo 7 O 24 ) multitransition-metal complex was prepared. This complex was deposited evenly on nano γ-alumina catalyst support. The partial reduction of cobalt (III)/ molybdate pre-catalyst was performed in a batch reactor with hydrogen gas at a pressure of 20 bars and temperature of 873 o K for 5 hours. The catalyst was characterized using FTIR, XRD, BET and TEM. The nano cobalt (III)/molybdenum catalyst was employed for hydrogenation reaction of carbon monoxide and carbon dioxide. The assessment of the catalyst was carried out at different temperature over a pressure range of 10-50 bars with various H 2 /CO ratios. This catalyst was found to be active, and stable for usage at high temperature and moderate pressure. The catalyst gave an excellent conversion of carbon monoxide to hydrocarbons (95%); it also converted 78% of carbon dioxide to carbon monoxide (73) and methane (5%). TEM image demonstrated catalyst has nearly spherical morphology with the average particle size of 46.86 nm.

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Raman studies on species in aqueous solutions. Part III. Vanadates, molybdates, and tungstates

Cited by 186 publications

References 0 publications

In situ Raman spectroscopy for the characterization of MoVW mixed oxide catalysts

In situ Raman spectroscopy for the characterization of MoVW mixed oxide catalysts

⁵¹V FT-nmr investigations of metavanadate ions in aqueous solutions

Hydrogenation of Carbon Monoxide and Carbon Dioxide over Nano γ-Alumina Supported Cobalt (III)/Molybdenum Catalyst

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Raman studies on species in aqueous solutions. Part III. Vanadates, molybdates, and tungstates

Cited by 186 publications

References 0 publications

In situ Raman spectroscopy for the characterization of MoVW mixed oxide catalysts

In situ Raman spectroscopy for the characterization of MoVW mixed oxide catalysts

51V FT-nmr investigations of metavanadate ions in aqueous solutions

Hydrogenation of Carbon Monoxide and Carbon Dioxide over Nano γ-Alumina Supported Cobalt (III)/Molybdenum Catalyst

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⁵¹V FT-nmr investigations of metavanadate ions in aqueous solutions