Models for heteropoly blues.  Degrees of valence trapping in vanadium(IV)- and molybdenum(V)-substituted Keggin anions

Altenau, Julianne J.; Pope, Michael T.; Prados, Ronald A.; So, Hyunsoo.

doi:10.1021/ic50144a042

Cited by 210 publications

(157 citation statements)

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“…All spectroscopic measurements were carried out with Spectralon ® (Labsphere) as reference material. HPA samples (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) …”

Section: In Situ Xasmentioning

confidence: 99%

“…An essential advance in the studies of optical spectra of catalysts of different stages of their transformation was achieved by applying the in situ diffuse reflectance UV/Vis/near-IR spectroscopy (DRS) [10,11], which proved to be a suitable technique for probing both d-d and charge transfer transitions at reaction temperature and under realistic gas compositions [12]. A number of groups have reported exsitu optical spectra [13,14,15,16,17]. It is known from these studies that the DRS method detects even small changes in spectral features connected with water loss or chemical reduction.…”

Section: Introductionmentioning

confidence: 99%

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The structure of molybdenum-heteropoly acids under conditions of gas-phase selective oxidation catalysis: a multi-method in situ study

Jentoft

Klokishner

Kröhnert

et al. 2003

Applied Catalysis A: General

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The present study focuses on the evidence about the existence of Keggin ions under various reactive conditions. The stability of the hydrated parent heteropoly acid (HPA) phases is probed in water, by thermal methods in the gas phase, by in situ X-ray diffraction and in situ EXAFS. An extensive analysis of the in situ optical spectra as UV-Vis-NIR in diffuse reflectance yields detailed information about the activated species that are clearly different from Keggin ions but are also clearly no fragments of binary oxides in crystalline or amorphous form. Infrared spectroscopy with CO as probe molecule is used to investigate active sites for their acidity. Besides -OH groups evidence for electron-rich Lewis acid sites was found in activated HPA. All information fit into a picture of a metastable defective polyoxometallate anion that is oligomerised to prevent crystallisation of binary oxides as the true nature of the "active HPA" catalyst. The as-synthesized HPA crystal is thus a pre catalyst and the precursor oxide mixture is the final deactivated state of the catalyst.

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“…All spectroscopic measurements were carried out with Spectralon ® (Labsphere) as reference material. HPA samples (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) …”

Section: In Situ Xasmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The structure of molybdenum-heteropoly acids under conditions of gas-phase selective oxidation catalysis: a multi-method in situ study

Jentoft

Klokishner

Kröhnert

et al. 2003

Applied Catalysis A: General

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“…Besides the oxygen ligand to metal charge transfer band (LMCT) there are absorption bands which can develop or disappear due to the optical d-d transitions in V 4+ and Mo 5+ and intervalence V 4+ -Mo 6+ and/or Mo 5+ -Mo 6+ optical transitions. Up to now, this spectroscopic method has been applied to the investigation of heteropoly compounds by some work groups, but all spectra were recorded ex situ [17][18][19][20][21]. The heteropoly compounds alter the spectroscopic behaviour due to the loss of water [22,23].…”

Section: Introductionmentioning

confidence: 99%

UV/Vis/near-IR spectroscopic characteristics of H4–xCsxPVMo11O40 (x = 0, 2) catalyst under different temperatures and gas atmospheres

Melsheimer

Kröhnert

Ahmad

et al. 2002

Phys. Chem. Chem. Phys.

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In order to understand the transformations of the Keggin-type H4-xCsxPVMo11 (x=0,2) compounds with rising temperature over long time stream of different gas athmospheres, in situ UV/Vis/near-IR spectroscopic studies were carried out. Diffuse reflectance spectra were recorded using an improved spectrometer and a suitable microreactor. Visible and near-IR peak intensities, peak positions and the band gap energies were determined from apparent absorption spectra. Propene, iso-propanol, water and the oxidation products were analyzed by GC. The experimental observed blue shift of the visible absorption band in the range of crystal water loss and the increase of the near -IR absorption were explained on the basis of quantum-mechanical calculations of the shapes and positions of the charge transfer and d-d bands arising from Mo 5+ -Mo 6+ and V 4+ -Mo 6+ pairs in intact and ill-defined fragments of the Keggin structure. It was concluded that with removal of crystal water during the action of He, He/H2O, propene, O2/propene and increasing temperature reduced species with protons located at the bridging oxygens promote a blue shift of the visible band, while a large number of ill-defined species form the near-IR part of the spectra in the temperature range 326 -600 K.

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“…Sodium phosphomolybdate hydrate (Na 3 Stock solutions of mixed addenda POMs were prepared by a one-pot synthesis adapted from Altenau et al [33], where specific molar ratios of Mo 12 -POM:W 12 -POM (3:9, 6:6, 9:3) were added to warm (~60-70°C) deionized water and stirred for 30 min. The final mixed addenda POM stock solutions had a concentration of approximately 0.1 M and a pH of 1.…”

Section: Methodsmentioning

confidence: 99%

Gas-Phase Fragmentation Pathways of Mixed Addenda Keggin Anions: PMo_12-nW_nO₄₀^3– (n = 0–12)

Gunaratne

Prabhakaran

Johnson

et al. 2015

J. Am. Soc. Mass Spectrom.

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Abstract. We report a collision-induced dissociation (CID) investigation of the mixed addenda polyoxometalate (POM) anions, PMo 12-n W n O 40 3-(n = 0-12). The anions were generated in solution using a straightforward single-step synthesis approach and introduced into the gas phase by electrospray ionization (ESI). Distinct differences in fragmentation patterns were observed for the range of mixed addenda POMs examined in this study. CID of molybdenum-rich anions, PMo 12-n W n O 40 3-(n = 0-2),generates an abundant doubly charged fragment containing seven metal atoms (M) and 22 oxygen atoms ( and M 7 O 22 2-fragment ions is different from that predicted by a random distribution, indicating substantial segregation of the addenda metal atoms in the POMs. Charge reduction of the triply charged precursor anion resulting in formation of doubly charged anions is also observed. This is a dominant pathway for mixed POMs having a majority (8-11) of W atoms and a minor channel for other precursors indicating a close competition between fragmentation and charge loss pathways in CID of POM anions.

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Models for heteropoly blues. Degrees of valence trapping in vanadium(IV)- and molybdenum(V)-substituted Keggin anions

Cited by 210 publications

References 19 publications

The structure of molybdenum-heteropoly acids under conditions of gas-phase selective oxidation catalysis: a multi-method in situ study

The structure of molybdenum-heteropoly acids under conditions of gas-phase selective oxidation catalysis: a multi-method in situ study

UV/Vis/near-IR spectroscopic characteristics of H4–xCsxPVMo11O40 (x = 0, 2) catalyst under different temperatures and gas atmospheres

Gas-Phase Fragmentation Pathways of Mixed Addenda Keggin Anions: PMo_12-nW_nO₄₀^3– (n = 0–12)

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Models for heteropoly blues. Degrees of valence trapping in vanadium(IV)- and molybdenum(V)-substituted Keggin anions

Cited by 210 publications

References 19 publications

The structure of molybdenum-heteropoly acids under conditions of gas-phase selective oxidation catalysis: a multi-method in situ study

The structure of molybdenum-heteropoly acids under conditions of gas-phase selective oxidation catalysis: a multi-method in situ study

UV/Vis/near-IR spectroscopic characteristics of H4–xCsxPVMo11O40 (x = 0, 2) catalyst under different temperatures and gas atmospheres

Gas-Phase Fragmentation Pathways of Mixed Addenda Keggin Anions: PMo12-nWnO403– (n = 0–12)

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Gas-Phase Fragmentation Pathways of Mixed Addenda Keggin Anions: PMo_12-nW_nO₄₀^3– (n = 0–12)