Bonding states of surface vanadium(V) oxide phases on silica: structural characterization by vanadium-51 NMR and Raman spectroscopy

Das, Nandini; Eckert, Hellmut; Hu, Hangchun; Wachs, Israel E.; Walzer, John F.; Feher, Frank J.

doi:10.1021/j100133a020

Cited by 282 publications

(314 citation statements)

References 8 publications

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“…These bands have been simply assigned to hydrated amorphous V 2 O 5 -like species because of their similarity to the Raman bands of V 2 O 5 crystallites. 12 It is interesting to note that as the loading increases from 1% to 12% V 2 O 5 , the last three bands blue shift from 506 to 523, 264 to 274, and 155 to 164 cm -1 . These blue shifts may be related to the shortening of some V-O bond lengths with increasing vanadia concentration on the silica surface since the V-O bond length is inversely correlated with the Raman vibrational frequency as established by Hardcastle and Wachs.…”

Section: Bulk Compositions Andmentioning

confidence: 92%

“…20,24 A sharp band at ∼1040 cm -1 was observed for all the dehydrated V 2 O 5 /SiO 2 samples, which has been assigned to the VdO stretching vibration of isolated VO 4 species. 12,13 The Raman band at 607 cm -1 due to the threemembered rings of the silica support significantly decreases with increasing vanadia loading, suggesting that the number of threemember siloxane rings decreases upon dispersion of the surface vanadium oxide species. In addition, two broad Raman bands appear at ∼1075 and ∼915 cm -1 , and their intensity does not change noticeably with increasing vanadia loading.…”

Section: X-ray Absorption Spectroscopy (Xanes)mentioning

confidence: 99%

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In Situ Spectroscopic Investigation of Molecular Structures of Highly Dispersed Vanadium Oxide on Silica under Various Conditions

et al. 1998

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The molecularly dispersed V 2 O 5 /SiO 2 supported oxides were prepared by the incipient wetness impregnation of 2-propanol solutions of V-isopropoxide. The experimental maximum dispersion of surface vanadium oxide species on SiO 2 was achieved at ∼12 wt % V 2 O 5 (∼2.6 V atoms/nm 2 ). The surface structures of the molecularly dispersed V 2 O 5 /SiO 2 samples under various conditions were extensively investigated by in situ Raman, UVvis-NIR DRS and XANES spectroscopies. The combined characterization techniques revealed that in the dehydrated state only isolated VO 4 species are present on the silica surface up to monolayer coverage. Interestingly, the three-member siloxane rings on the silica surface appear to be the most favorable sites for anchoring the isolated, three-legged (SiO) 3 VdO species. Hydration dramatically changes the molecular structure of the surface vanadium oxide species. The specific structure of the hydrated surface vanadium oxide species is dependent on the degree of hydration. The molecular structure of the fully hydrated vanadium oxide species closely resembles V 2 O 5 ‚nH 2 O gels, rather than V 2 O 5 crystallites. The fully hydrated surface vanadium oxide species are proposed to be chain and/or two-dimensional polymers with highly distorted square-pyramidal VO 5 connected by V-OH-V bridges, which are stabilized on the silica surface by the sixth neighbor of Si-OH hydroxyls via Si-OH‚‚‚V hydrogen bonds. In analogy to the hydration process, alcoholysis occurs during methanol chemisorption, and similar molecular structures are proposed to interpret the interaction between methanol molecules and the surface vanadium oxide species on silica.

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Section: Bulk Compositions Andmentioning

confidence: 92%

Section: X-ray Absorption Spectroscopy (Xanes)mentioning

confidence: 99%

In Situ Spectroscopic Investigation of Molecular Structures of Highly Dispersed Vanadium Oxide on Silica under Various Conditions

et al. 1998

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“…Solid state 51 V nuclear magnetic resonance (NMR) is a suitable technique to investigate supported V 5+ oxides since the nuclear spin of vanadium is 7 2 , its natural abundance is almost 100% and its capability to discriminate between different coordination environments of vanadium oxides [106][107][108][109][110][111][112][113][114][115]. The presence of paramagnetic species, such as V 4+ , may prevent to observe NMR signals since such species broadens the NMR signal, and consequently, the signal due to V 5+ can be lost.…”

Section: Bm Weckhuysen De Keller / Catalysis Today 78 (2003) 25-46mentioning

confidence: 99%

Chemistry, spectroscopy and the role of supported vanadium oxides in heterogeneous catalysis

2003

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Supported vanadium oxide catalysts are active in a wide range of applications. In this review, an overview is given of the current knowledge available about vanadium oxide-based catalysts. The review starts with the importance of vanadium in heterogeneous catalysis, a discussion of the molecular structure of vanadium in water and in the solid state and an overview of the spectroscopic techniques enabling to study the chemistry of supported vanadium oxides. In the second part, it will be shown that advanced spectroscopic tools can be used to obtain detailed information about the coordination environment and oxidation state of vanadium oxides during each stage of the life-span of a heterogeneous catalyst. Three topics will be discussed: (1) the molecular structure of supported vanadium oxide catalysts under hydrated, dehydrated and reduced conditions, including the parameters, which influence the molecular structures formed at the surface of the support oxide; (2) elucidation of the active surface vanadium oxide during the oxidation of methanol to formaldehyde, the reaction mechanism and the vanadium oxide-support effect; and (3) deactivation of fluid catalytic cracking (FCC) catalysts by migration of vanadium oxides and the development of a method preventing the structural breakdown of zeolites by trapping the mobile vanadium oxides in an aluminum oxide coating.

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“…44 Additionally, the SiO 2 support band at ∼480 cm −1 is likely an artifact since it has not been seen in previous Cabosil EH-5 SiO 2 spectra. 40,44 Several samples exhibit broad bands at ∼913 and ∼1077 cm −1 which are characteristic of Si(-O − ) 2 and Si-O − functionalities, respectively, that have been perturbed by vanadium oxide deposition 44,45 …”

Section: Dalton Transactions Papermentioning

confidence: 99%

Anomalous reactivity of supported V2O5 nanoparticles for propane oxidative dehydrogenation: influence of the vanadium oxide precursor

et al. 2013

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The oxidative dehydrogenation (ODH) of propane to propylene by supported vanadia catalysts has received much attention in recent years, but different reactivity trends have been reported for this catalytic reaction system. In the present investigation, the origin of these differing trends are investigated with synthesis of supported V/SiO 2 , V/TiO 2 , and V/Al 2 O 3 catalysts prepared with three different vanadium

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Bonding states of surface vanadium(V) oxide phases on silica: structural characterization by vanadium-51 NMR and Raman spectroscopy

Cited by 282 publications

References 8 publications

In Situ Spectroscopic Investigation of Molecular Structures of Highly Dispersed Vanadium Oxide on Silica under Various Conditions

In Situ Spectroscopic Investigation of Molecular Structures of Highly Dispersed Vanadium Oxide on Silica under Various Conditions

Chemistry, spectroscopy and the role of supported vanadium oxides in heterogeneous catalysis

Anomalous reactivity of supported V2O5 nanoparticles for propane oxidative dehydrogenation: influence of the vanadium oxide precursor

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