Selective oxidation of n-pentane on 12-molybdovanadophosphoric acids

Centi, Gabriele; Nieto, J.M. López; Iapalucci, C.; Brückman, K.; Serwicka, Ewa M.

doi:10.1016/s0166-9834(00)81117-3

Cited by 78 publications

(25 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…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%

See 1 more Smart Citation

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

View full text Add to dashboard Cite

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.

show abstract

“…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

View full text Add to dashboard Cite

show abstract

“…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.

View full text Add to dashboard Cite

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.

show abstract

“…The width of the feature suggests that it is a superposition of several single bands, possibly different C 6 isomers. Alternatively, the band could be assigned to cyclopentenyl cations, which were proposed as causes of deactivation by Luzgin et al (35), who monitored the isomerization of n-pentane at room temperature by 13 C-MAS-NMR. Bands of more highly conjugated species were not detected; both, our observations with the n-butane reaction and Pazé's (22) results suggest that the reaction temperature (max.…”

Section: N-pentane Isomerizationmentioning

confidence: 99%

“…Diffuse reflectance spectroscopy in the ultraviolet and visible region is a suitable technique for studying electronic transitions of heterogeneous catalysts (13)(14)(15)(16)(17)(18). Additionally, the technique is potentially very sensitive for the detection of adsorbed reaction intermediates or side products, depending on the chromophores present in these species.…”

Section: Introductionmentioning

confidence: 99%

Isomerization of n-butane and of n-pentane in the presence of sulfated zirconia: formation of surface deposits investigated by in situ UV–vis diffuse reflectance spectroscopy

Ahmad

Melsheimer

Jentoft

et al. 2003

Journal of Catalysis

View full text Add to dashboard Cite

Catalytic performance and formation of carbonaceous deposits were studied simultaneously during alkane isomerization over sulfated zirconia in a fixed bed flow reactor with an optical window for in situ UV-vis diffuse reflectance spectroscopy. The reactions of n-butane (5 kPa) at 358 and 378 K and of n-pentane (0.25 kPa) at 298 and 308 K passed within 5 h or less through an induction period, a conversion maximum, and a period of deactivation; a steady activity of 41 and 47 µmol g -1 h -1 (isobutane formation) and ≈2.5 µmol g -1 h -1 (isopentane, both temperatures) remained. UV-vis spectra indicate the formation of unsaturated surface deposits; the band positions at 310 nm (n-butane reaction) and 330 nm (npentane) are within the range of monoenic allylic cations. More highly conjugated allylic cations (bands at 370 and 430 nm) became evident during n-butane reaction at 523 K. The chronology of events suggests that the surface deposits are (i) a result only of the bimolecular and not the monomolecular reaction mechanism, and (ii) are formed in a competitive reaction to the alkane products.

show abstract

Selective oxidation of n-pentane on 12-molybdovanadophosphoric acids

Cited by 78 publications

References 32 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

Isomerization of n-butane and of n-pentane in the presence of sulfated zirconia: formation of surface deposits investigated by in situ UV–vis diffuse reflectance spectroscopy

Contact Info

Product

Resources

About