Redox Properties of Vanadium Ions in SBA-15-Supported Vanadium Oxide:  An FTIR Spectroscopic Study

Venkov, Tzvetomir; Heß, Christian; Jentoft, Friederike C.

doi:10.1021/la062269n

Cited by 35 publications

(58 citation statements)

References 55 publications

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“…An adsorbate-type structure of the active site allowing dynamical response will be useful whereas a closely packed 3-D crystalline state will hinder such a process with high activation barriers. Such ''adsorbatelike'' active phases [77,78] can be identified with probe molecule reactions [79][80][81][82][83][84][85][86] and have been rationalized for covering some bulk catalysts [13,42,[87][88][89][90][91] as consequence of surface energy minimization.…”

Section: Size and Functions Of Active Sitesmentioning

confidence: 99%

Active Sites for Propane Oxidation: Some Generic Considerations

Schlögl

2011

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Based on experimental observations about structure and dynamics of the reactive surface of the M1 phase some considerations are made about the nature and size of active sites. In analyzing the stoichiometry of the reactions following activation of propane it occurs that for dehydrogenation small sites are desirable being just sufficient to re-activate oxygen without kinetic hindrance. For deeper oxidation to acrylic acid (AA) the sites should be larger to accommodate all redox equivalents and oxygen species required for one transformation. A qualitative model for size and composition of the active site is made. It is likely that the active site consists on a VxOy species of strictly 2-D nature. This follows the structural suggestion for the active site on the a-b-plane of the M1 structure. The role of Te in moderating the active site is discussed. The suggestions are discussed in comparing requirements for oxidative dehydrogenation of propane (ODP) with those for AA synthesis.

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Section: Size and Functions Of Active Sitesmentioning

confidence: 99%

Active Sites for Propane Oxidation: Some Generic Considerations

Schlögl

2011

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“…In summary, the UV-Vis and Raman data suggest that after dehydration both isolated and small aggregates of polymerized VO 4 units with tetrahedrally coordinated V ions are present. 10 After the Raman and UV-Vis analysis the sample was cooled to room temperature and transferred to the XPS chamber. Figure 3 shows the V2p 3/2 emission of dehydrated SBA-15 supported vanadium oxide (top spectrum) together with a least-square fit to the data.…”

Section: +mentioning

confidence: 99%

“…[7][8][9] However, a recent IR study provides evidence for the presence of V-O-V implying vanadia dimers or polymers. 10 Previously, the presence of polymeric species on silica SBA-15 supported vanadia had been suggested on the basis of UV-Vis results.…”

Section: Introductionmentioning

confidence: 99%

Direct correlation of the dispersion and structure in vanadium oxide supported on silica SBA-15

Heß

2007

Journal of Catalysis

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Raman, UV-Vis and X-ray photoelectron spectroscopy were combined in one experimental setup to directly study the interplay between structure and dispersion of SBA-15 supported vanadium oxide during dehydration. The fully hydrated catalyst is slightly reduced but consists mainly of V 5+ species with pseudo-octahedral V coordination strongly resembling the xerogel V 2 O 5 ·1.2H 2 O. After dehydration a highly dispersed surface anadium oxide species with tetrahedrally coordinated vanadium and significantly smaller ensemble size is formed. v

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“…7 Analytical investigations indicate that monomeric and/or associated vanadium species are present on the surface of the support materials studied here. 8,9 The generally accepted reaction network 10 of ODP is depicted in Figure 1.…”

Section: Introductionmentioning

confidence: 99%

“…In the case of silica as a support material, the presence of dimeric and/or polymeric species at low loadings has only recently been observed for SBA-15-supported vanadium oxide. 9 At very high loadings, activity and selectivity decrease because of formation of crystalline V 2 O 5 .…”

Section: Introductionmentioning

confidence: 99%

Potential of High-Frequency EPR for Investigation of Supported Vanadium Oxide Catalysts

et al. 2008

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Supported vanadium oxide catalysts were studied by high-frequency EPR for determination of the paramagnetic vanadium oxidation states vanadium(IV) and vanadium(III). TiO 2 -, γ-Al 2 O 3 -, and SiO 2 (SBA-15)-supported catalysts were investigated before and after being used for the oxidative dehydrogenation of propane. While the SBA-15-supported catalyst exhibits only one distinct position of vanadium species with the oxidation state IV, Al 2 O 3 reveals a distribution of vanadium(IV) sites. For this support material formation of oxoradicals has been observed, indicating its capability for trapping electrons during the catalytic cycle. The TiO 2 -supported material apparently does not stabilize vanadium(IV), which can be attributed to either a high mobility of existing oxygen vacancies or the competitive capability of titanium(IV) surface states to trap electrons. Titanium in its oxidation state of vanadium(III) and surface-trapped O 2 (-) species were identified as potential electron sinks in the case of the TiO 2 -supported catalyst. The increase in catalytic activity in the order of SBA-15 < Al 2 O 3 < TiO 2 therefore could be caused by different reduction mechanisms depending on the chosen support material. No vanadium in its oxidation state III was detected in any of the samples, which indicates that such species are either short lived or not existent during the oxidative dehydrogenation of propane.

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Redox Properties of Vanadium Ions in SBA-15-Supported Vanadium Oxide: An FTIR Spectroscopic Study

Abstract: The state of vanadium ions in VxOy/SBA-15 (2.7 wt % V) was studied with FTIR spectroscopy using CO and NO as probe molecules. Neither CO (at 85 K) nor NO (at RT) adsorb on the oxidized sample because of the coordinative saturation of V 5+ ions and the covalent character of the

Cited by 35 publications

References 55 publications

Active Sites for Propane Oxidation: Some Generic Considerations

Active Sites for Propane Oxidation: Some Generic Considerations

Direct correlation of the dispersion and structure in vanadium oxide supported on silica SBA-15

Potential of High-Frequency EPR for Investigation of Supported Vanadium Oxide Catalysts

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