Molecular design of supported metal oxide catalysts: An initial step to theoretical models

Wachs, Israel E.; Deo, Goutam; Vuurman, Michael A.; Hu, Hangchun; Kim, Du Soung; Jehng, Jih‐Mirn

doi:10.1016/0304-5102(93)80046-w

Cited by 70 publications

(56 citation statements)

References 24 publications

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“…This model, which might be called the pyramidal model, predicts the existence of one vibrational mode which is predominantly the V@O stretch, that should be close to that found in simple V@O structures like VOX 3 , with X = F, Cl, Br or I. This mode is indeed reported at around 1030 cm À1 by many authors [10][11][12][13][14][15][16]. The structure of the pyramidal model also complies with EXAFS studies [17].…”

Section: Introductionsupporting

confidence: 55%

A new model for the molecular structure of supported vanadium oxide catalysts

Gijzeman

Lingen

Lenthe

et al. 2004

Chemical Physics Letters

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Raman spectroscopy experiments found the V@O stretching frequency for the supported VO 4 species to decrease with increasing catalyst temperature. Calculations on the vibrational frequencies of several models using density functional theory show that a consistent description of the experimental data can be obtained if we assume that the VO 4 species are anchored to the oxidic surface by one V-O bond only, in contrast to the traditional pyramidal model, which assumes three V-O support bonds and one V@O. The proposed VO 3 structure points away from the surface and consists of one V@O unit and an active oxygen ÔmoleculeÕ loosely bound to the vanadium atom, a peroxide species.

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Section: Introductionsupporting

confidence: 55%

A new model for the molecular structure of supported vanadium oxide catalysts

Gijzeman

Lingen

Lenthe

et al. 2004

Chemical Physics Letters

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“…It is known from experiment [34][35][36][37][38][39] that hydrated tetrahedral vanadia species exist. Moreover, this result is in line with the observation that surface hydroxyl groups are reactive towards the metal oxide adsorbates [40].…”

Section: Anatasesupporting

confidence: 88%

Reaction of surface hydroxyl groups with VO4H3 on anatase surfaces

2005

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“…The latter is of importance in order to better understand vanadium oxide-support effects. For these reasons, the molecular structures of supported VO x on a variety of support materials, under various conditions and over a broad range of vanadium oxide loadings have been the subject of many spectroscopic studies including IR [8][9][10][11][12][13][14][15], Raman [15][16][17][18][19][20][21][22][23][24], UV-vis-NIR [25][26][27][28][29] and EXAFS [30][31][32][33][34][35][36].…”

Section: Introductionmentioning

confidence: 99%

Hydration effects on the molecular structure of silica-supported vanadium oxide catalysts: A combined IR, Raman, UV–vis and EXAFS study

Keller

Visser

Soulimani

et al. 2007

Vibrational Spectroscopy

125

130

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The effect of hydration on the molecular structure of silica-supported vanadium oxide catalysts with loadings of 1-16 wt.% V has been systematically investigated by infrared, Raman, UV-vis and EXAFS spectroscopy. IR and Raman spectra recorded during hydration revealed the formation of V-OH groups, characterized by a band at 3660 cm À1. Hydroxylation was found to start instantaneously upon exposure to traces of water, reflecting a very high sensitivity of the supported vanadium oxide catalysts for H 2 O. Further hydration resulted in the appearance of a V-O-V vibration band located around 700 cm À1 pointing to the formation of di-or polymeric species. EXAFS analysis at 77 K indicated structural changes as the oxygen coordination changed from four to five. Moreover, a VÁ Á ÁV contribution was detected for the hydrated species. The IR, Raman and UV-vis data suggested a pyramidal anchoring of the dehydrated VO x species, whereas, the EXAFS data pointed to the presence of single V-O-Si bonded VO x species. This difference is attributed to water condensation effects at 77 K during EXAFS acquisition, resulting in a partial re-hydroxylation of the dehydrated samples, as confirmed by complementary IR and Raman analysis. as well as literature led to a reaction scheme in which a monomeric VO x species anchored by three Si-O-V bonds to the silica support (pyramidal-type structure) is transformed into a monomeric VO x species anchored by one Si-O-V bond (umbrella-type structure) by partial hydration of the catalyst material. This results in the formation of both V-O-H and Si-O-H bonds. At higher water pressures, larger vanadium oxide clusters are formed due to full hydration of the catalyst surface and a de-attachment of the vanadium oxide from the support surface. The results of this study provide evidence, that an umbrella-type structure (i.e., Si-O-V O(OH) 2 ) could be present under catalytic conditions where H 2 O is a reaction product (e.g., partial oxidation of methanol to formaldehyde and oxidative dehydrogenation of alkanes). In other words, both the pyramidal ((Si-O) 3 -V O) and the umbrella (Si-O-V O(OH) 2 ) model can exist at a support surface, their relative ratio depending on the hydration degree of the catalyst material. This study also illustrates that a corroborative characterization requires the use of multiple spectroscopic techniques applied at the same samples under almost identical measuring conditions. #

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Molecular design of supported metal oxide catalysts: An initial step to theoretical models

Cited by 70 publications

References 24 publications

A new model for the molecular structure of supported vanadium oxide catalysts

A new model for the molecular structure of supported vanadium oxide catalysts

Reaction of surface hydroxyl groups with VO4H3 on anatase surfaces

Hydration effects on the molecular structure of silica-supported vanadium oxide catalysts: A combined IR, Raman, UV–vis and EXAFS study

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