Physicochemical characterization of V-silicalite

Centi, Gabriele; Perathoner, Siglinda; Trifirò, F.; Aboukaı̈s, Antoine; Aissi, C. F.; Guelton, M.

doi:10.1021/j100185a042

Cited by 356 publications

(213 citation statements)

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“…Two bands at 410 and 450 nm indicate that the extra framework V 5+ ions are formed in V-MCM-41. However, the UV-vis electronic absorption of polymerized vanadium oxides supported on SiO 2 also appears in the 250-350 nm region [36]. The bands at 250 and 320 nm are observed in UV-visible diffused reflectance spectrum of supported vanadium oxides.…”

Section: Identifying the Isolated Vanadium Sites In V-mcm-41mentioning

confidence: 97%

Identifying the isolated transition metal ions/oxides in molecular sieves and on oxide supports by UV resonance Raman spectroscopy

2003

Journal of Catalysis

142

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Section: Identifying the Isolated Vanadium Sites In V-mcm-41mentioning

confidence: 97%

Identifying the isolated transition metal ions/oxides in molecular sieves and on oxide supports by UV resonance Raman spectroscopy

2003

Journal of Catalysis

142

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“…This similarity of the local geometry might be another indication that vanadium is not entering into a true framework position, together with the fact that V 4 species with tetrahedral symmetry (namely, in a framework site) could not be observed by ESR technique as well as with the absence of protonated template resulting from the thermoanalytical measurements. At the same time, these vanadium species are strongly anchored to the aluminophosphate framework, since leaching experiments with solutions of ammonium acetate, known to eliminate vanadium polymeric surface species [50], have shown that the ESR signals are almost unaltered after such a treatment. The occurrence of polynuclear oxidic vanadium species in the samples that show a lower amount of ESR-visible V 4 than vanadium amount found by elemental analysis (e.g.…”

Section: Optimal Conditions For Vapo-11 Synthesismentioning

confidence: 99%

“…This symmetry can be reached in defect sites of the framework. The model proposed by Prakash and Kevan [50], in which the V O 2 cation is attached to the surface with two framework oxygens and having three water molecules co-ordinated to the central ion is the most plausible, even though we have not yet found evidence for the presence of protonated template molecules in the VAPO-11 and VAPO-41 materials, necessary to compensate for the charge balancing of the defect due to the vanadium linkages as well as for a possible OH À ligand instead of one of the water ligands.…”

Section: Optimal Conditions For Vapo-11 Synthesismentioning

confidence: 99%

On the synthesis of vanadium containing molecular sieves by experimental design from a VOSO4·5H2O·Al(iPrO)3·Pr2NH·H2O gel: occurrence of VAPO-41 as a secondary structure in the synthesis of VAPO-11

Frunză¹,

Voort²,

Vansant³

et al. 2000

Microporous and Mesoporous Materials

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“…The UV-VIS absorption bands also appear in a similar region for polymerized vanadium oxides supported on SiO 2 . 16 A band at 250 nm together with a shoulder at 320 nm is observed in the UV-VIS absorption spectrum of vanadium oxide. Therefore, the 244 nm laser line can excite both the band centered at 275 nm associated with the isolated vanadium species and the band centered at 250 nm of polymerized vanadium oxides.…”

mentioning

confidence: 94%

Direct spectroscopic evidence for vanadium species in V-MCM-41 molecular sieve characterized by UV resonance Raman spectroscopy

Xiong

et al. 2000

Chem. Commun.

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Vanadium species in tetrahedral and octahedral coordination in V-MCM-41 molecular sieve are characterized by UV resonance Raman bands at 1070 and 930 cm 21 respectively.Vanadium-substituted molecular sieves have been found to be excellent catalysts for many selective oxidation reactions. [1][2][3] In particular, V-MCM-41 has drawn much interest owing to its large pore diameter which is suitable for selective oxidation of large organic compounds. [4][5][6] The catalytic activity and selectivity of vanadium-substituted molecular sieves are directly related to the coordination structures of the vanadium species in the molecular sieves. In general, three forms of vanadium species, isolated tetrahedral, two-dimensional octahedral species and crystalline V 2 O 5 , are believed to be present. 4,5,7,8 The coordination structure of vanadium species in V-MCM-41 has been investigated by 51 V NMR, UV-VIS absorption spectroscopy and many other techniques, 4,5,8 but identification of vanadium species in tetrahedral or octahedral coordination environments is not straightforward. Raman spectroscopy is a potentially viable technique for the study of the structure of vanadium species in V-MCM-41, since it has been used to characterize supported vanadium oxides with both tetrahedral and octahedral coordination structures. 9,10 However, there have been relatively few Raman studies on vanadium-substituted MCM-41, 8 mainly because of fluorescence interference and the low sensitivity of conventional Raman spectroscopy. The limited amount of substituted vanadium atoms also hinders the application of Raman spectroscopy in characterization of vanadium atoms in V-MCM-41.UV Raman spectroscopy has been proved to be a powerful technique for the study of catalysts and other solids, 11,12 especially, for the identification of isolated transition metal atoms substituted in the framework of molecular sieves 13 or grafted on metal oxides. 14 An increase in the intensity of Raman signal and decrease in the intensity of fluorescence background help to increase the sensitivity of the Raman spectra. Moreover, the resonance Raman effect will selectively enhance the intensity of the Raman signal by several orders of magnitude when the excitation laser line is close to the electronic transition absorption of the samples.In this work, for the first time, we study the different vanadium species in V-MCM-41 using UV resonance Raman spectroscopy. Based on the UV resonance Raman effect the vanadium species in tetrahedral and octahedral environments in V-MCM-41 can be successfully identified by UV resonance Raman spectroscopy.MCM-41 and V-MCM-41 were synthesized according to the method reported in the literature. 4 V-MCM-41 samples which possess Si/V ratios of 250, 125 and 60 are denoted V-MCM-41 (250), V-MCM-41 (125) and V-MCM-41 (60), respectively. The as-synthesized samples show XRD patterns matching well with these reported in the literature. 4,5,15 UV Raman spectra were recorded on a homemade UV Raman spectrometer. 12 244 and 488 nm lines from a Innova 3...

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Physicochemical characterization of V-silicalite

Cited by 356 publications

References 0 publications

Identifying the isolated transition metal ions/oxides in molecular sieves and on oxide supports by UV resonance Raman spectroscopy

Identifying the isolated transition metal ions/oxides in molecular sieves and on oxide supports by UV resonance Raman spectroscopy

On the synthesis of vanadium containing molecular sieves by experimental design from a VOSO4·5H2O·Al(iPrO)3·Pr2NH·H2O gel: occurrence of VAPO-41 as a secondary structure in the synthesis of VAPO-11

Direct spectroscopic evidence for vanadium species in V-MCM-41 molecular sieve characterized by UV resonance Raman spectroscopy

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