Raman Spectra of Rings in Silicate Materials

Tallant, D. R.; Bunker, Bruce C.; Brinker, C. Jeffrey; Balfe, Carol A.

doi:10.1557/proc-73-261

Cited by 39 publications

(28 citation statements)

References 14 publications

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“…As discussed previously [33], the spectrum of blank SBA-15 (spectrum (a)) shows Raman features around 485 and 977 cm -1 , which are attributed to cyclic tetrasiloxane rings of the silica support (D1 defect mode) [48] and the Si-OH stretching vibration of surface hydroxyl groups [49], respectively. In addition, weaker Raman bands appeared around 600 cm -1 and 810 cm -1 , which are assigned to cyclic trisiloxane rings (D2 defect mode) and the symmetrical Si-O-Si stretching mode, respectively [49]. Functionalization of SBA-15 with APTMS and subsequent transformation into the ammonium salt leads to the appearance of new major bands at 940 and 1040 cm -1 , respectively (spectrum (b)).…”

Section: Vo X /Sba-15mentioning

confidence: 52%

The mechanism for the controlled synthesis of highly dispersed vanadia supported on silica SBA-15

Heß

Wild

Schlögl

2006

Microporous and Mesoporous Materials

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The mechanism for the controlled synthesis of highly dispersed vanadia supported on mesoporous silica SBA-15 (VO x /SBA-15) is elucidated using X-ray photoelectron spectroscopy (XPS), Raman and diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS). The synthesis consists of functionalization of SBA-15 using 3-aminopropyltrimethoxysilane (APTMS) followed by HCl treatment, anion exchange of decavanadate (V 10 O 28 6-) and calcination to yield the final material. Spectroscopic analysis yields that APTMS is grafted onto the surface via hydroxyl groups. Under ambient conditions, protonated APTMS on SBA-15 is largely hydrolyzed and present in its bidentate and tridentate form. Detailed XPS analysis reveals a strong influence of surface water on the resulting structure of APTMS on SBA-15. Under dry conditions, the protonated APTMS molecules on SBA-15 adopt the monodentate and bidentate form. During the anion exchange reaction, decavanadate is incorporated intactly into the pores, without any changes in the structure of the organic framework. In the calcination step, decavanadate is decomposed and vanadia is anchored onto the surface of SBA-15 via silanol groups resulting in highly dispersed surface vanadia species, while the organic resiues are fully removed from the pores of the silica matrix. d

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Section: Vo X /Sba-15mentioning

confidence: 52%

The mechanism for the controlled synthesis of highly dispersed vanadia supported on silica SBA-15

Heß

Wild

Schlögl

2006

Microporous and Mesoporous Materials

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“…In contrast to the vanadia samples, the blank SBA-I5 support gives rise to only one Raman band at 987 cm )1 , which is characteristic of the Si-OH stretching mode of surface hydroxyls [36]. Obviously, upon grafting of vanadia, its intensity decreases as a result of the reaction of Si-OH with the vanadi a precursor.…”

Section: Synthesis Of Vo X /Sba-15mentioning

confidence: 96%

Partial Oxidation of Methanol Over Highly Dispersed Vanadia Supported on Silica SBA-15

et al. 2005

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The partial oxidation of methanol to formaldehyde (FA) was studied over highly dispersed vanadia supported on mesoporous silica SBA-15 (VO x /SBA-15). VO x /SBA-15 catalysts were prepared by a novel grafting/ion-exchange method and characterized using UV-VIS-and Raman spectroscopy. The resulting surface vanadium oxide species (0-2.3 V/nm 2 ), grafted on the inner pores of the SBA-15 silica matrix, consist of tetrahedrally coordinated monomeric and polymeric vanadia. The VO x /SBA-15 catalysts are active and highly selective for the production of FA between 300 and 400°C. Comparison of the reactivity results with literature data reveals that a better catalytic performance can be obtained over vanadia supported on mesoporous silica in comparison with conventional silica samples with the same vanadium loading. Raman characterization of the catalyst after reaction at high conversion indicates that dispersed vanadia partly agglomerates into vanadia crystallites during methanol oxidation.

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“…Besides the Raman band at 1040 cm -1 , the dehydrated vanadia samples give rise to additional bands at 915 cm -1 and 1072 cm -1 , which can be assigned to Si-O -and Si(-O -) 2 functionalities indicating the formation of V-O-Si [29,23]. In contrast to the vanadia samples, the blank SBA-15 support gives rise to only one Raman band at 987 cm -1 , which is characteristic of the Si-OH stretching mode of surface hydroxyls [30]. Obviously, upon grafting of vanadia, its intensity decreases as a result of the reaction of Si-OH with the vanadia precursor.…”

Section: Spectroscopic Characterization Of Vo X /Sba-15mentioning

confidence: 99%

Characterization of the synthesis and reactivity behavior of nanostructured vanadia model catalysts using XPS and vibrational spectroscopy

Heß

2006

Surface Science

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Nanostructured vanadia model catalysts, i.e. highly dispersed vanadium oxide supported on mesoporous silica SBA-15 (VO x /SBA-15), were prepared. The mechanism for the synthesis of VO x /SBA-15 was elucidated by detailed characterization of the individual synthesis steps using XPS and vibrational spectrocopy. The resulting surface vanadium oxide species (0 -2.3 V/nm 2 ), grafted on the inner pores of the SBA-15 silica matrix, consists of tetrahedrally coordinated vanadia as inferred from UV-VIS-and Raman spectroscopy. The prepared vanadia model catalysts were tested in the partial oxidation of methanol to formaldehyde yielding high formaldehyde selectivities of 94% at 350ºC. XPS and Raman analysis of the catalyst after reaction reveal the presence of methoxy as well as a significant amount of carbonaceous species on the surface. Our results demonstrate that a detailed understanding of partial oxidation reactions requires the combination of complementary spectroscopic techniques ultimately within one experimental set-up.

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Raman Spectra of Rings in Silicate Materials

Cited by 39 publications

References 14 publications

The mechanism for the controlled synthesis of highly dispersed vanadia supported on silica SBA-15

The mechanism for the controlled synthesis of highly dispersed vanadia supported on silica SBA-15

Partial Oxidation of Methanol Over Highly Dispersed Vanadia Supported on Silica SBA-15

Characterization of the synthesis and reactivity behavior of nanostructured vanadia model catalysts using XPS and vibrational spectroscopy

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