X-Ray absorption and X-ray diffraction studies on molybdenum doped vanadium pentoxide

Haaß, Frank; Adams, Andreas H.; Buhrmester, Thorsten; Schimanke, Guido; Martin, Manfred; Fueß, H.

doi:10.1039/b307158h

Cited by 28 publications

(22 citation statements)

References 9 publications

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“…The (MoVW) dioxide and (MoV) dioxide obtained from reduction of the Mo 5 O 14 -type materials exhibit a reduced average valence of the V centers ( Figure 7) compared the Mo centers ( Figure 6). This is in agreement with previous reports on the average valence of V centers in vanadium oxides doped with up to 10 % molybdenum [22]. There, the authors did not detect changes in the Mo average valence but reduction of vanadium to preserve electro neutrality of the materials.…”

Section: Influence Of Vanadium On Electronic and Geometric Structuresupporting

confidence: 82%

Structure stabilizing effect of tungsten in mixed molybdenum oxides with Mo5O14-type structure

et al. 2007

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Bulk structural properties of single phase crystalline (Mo 0.91 V 0.09 ) 5 O 14 and (Mo 0.68 V 0.23 W 0.09 ) 5 O 14 materials were investigated using in situ X-ray diffraction and in situ X-ray absorption spectroscopy at three metal edges. Temperature programmed experiments in reducing (propene) and oxidizing (oxygen) atmosphere and isothermal redox experiments at 773 K revealed differences in the bulk properties of the two phases studied. A structure stabilizing effect of tungsten in (MoVW) 5 O 14 under oxidizing conditions was found. Moreover, tungsten centers in a (MoVW) dioxide material exert a structure-directing effect towards re-oxidation to a Mo 5 O 14 -type structure.

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Section: Influence Of Vanadium On Electronic and Geometric Structuresupporting

confidence: 82%

Structure stabilizing effect of tungsten in mixed molybdenum oxides with Mo5O14-type structure

et al. 2007

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“…Our linear fit for the position of the absorption feature labelled 'A' in figure 1 (1s fi 4p transition) as a function of vanadium oxidation state for pure vanadium oxides has smaller standard deviations than the corresponding fit for the main-edge positions. This makes the A position a better candidate for the vanadium oxidation state estimation, as also shown by Haaß et al [7]. Figure 2 shows the energy shift in the A absorption feature for V 2 O 5 , VO 2 , V 2 O 3 and VO together with the linear fit (correlation factor of 0.999).…”

Section: V-o Reference Xanes Spectramentioning

confidence: 71%

An in-situ Reduction/Oxidation XAS Study on the EL10V8 VOx/TiO2(Anatase) Powder Catalyst

et al. 2006

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The structural changes of the supported vanadium oxide in the V 2 O 5 /TiO 2 (anatase) EUROCAT EL10V8 powder catalyst during reduction and oxidation at 420 and 490°C were studied with in-situ X-ray absorption spectroscopy (XAS). The Vanadium K-edge XAS results are compared with pure bulk V 2 O 5 . For the reduction-oxidation cycle at 420°C, similar structural changes as for bulk V 2 O 5 were observed for the supported vanadium oxide: a reduction to the VO 2 structure and re-oxidation back to V 2 O 5 . After reduction at 490°C however, a different structure was obtained: very regular ''VO 6 '' octahedra with a V 2.8+ valence. This may point to a structural support effect.KEY WORDS: EUROCAT EL10V8; supported vanadium oxide; absorption spectroscopy; VO x /TiO 2 (anatase); in-situ XAS; V 2 O 5 .

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“…After the calcination procedure the pellets were quenched in liquid nitrogen to stabilise the crystalline phases formed. The details of the solid state preparation can be found in Adams et al 22,23 Hydrochemical preparation routes. The second method of preparation is based on aqueous solutions of the ammonium salts acidified with nitric acid.…”

Section: Preparation Techniques For Mixed Oxide Catalystsmentioning

confidence: 99%

Heterogeneously catalysed partial oxidation of acrolein to acrylic acid—structure, function and dynamics of the V–Mo–W mixed oxides

Kampe

Giebeler

Samuelis

et al. 2007

Phys. Chem. Chem. Phys.

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The major objective of this research project was to reach a microscopic understanding of the structure, function and dynamics of V-Mo-(W) mixed oxides for the partial oxidation of acrolein to acrylic acid. Different model catalysts (from binary and ternary vanadium molybdenum oxides up to quaternary oxides with additional tungsten) were prepared via a solid state preparation route and hydrochemical preparation of precursors by spray-drying or crystallisation with subsequent calcination. The phase composition was investigated ex situ by XRD and HR-TEM. Solid state prepared samples are characterised by crystalline phases associated to suitable phase diagrams. Samples prepared from crystallised and spray-dried precursors show crystalline phases which are not part of the phase diagram. Amorphous or nanocrystalline structures are only found in tungsten doped samples. The kinetics of the partial oxidation as well as the catalysts' structure have been studied in situ by XAS, XRD, temperature programmed reaction and reduction as well as by a transient isotopic tracing technique (SSITKA). The reduction and re-oxidation kinetics of the bulk phase have been evaluated by XAS. A direct influence not only of the catalysts' composition but also of the preparation route is shown. Altogether correlations are drawn between structure, oxygen dynamics and the catalytic performance in terms of activity, selectivity and long-term stability. A model for the solid state behaviour under reaction conditions has been developed. Furthermore, isotope exchange experiments provided a closer image of the mechanism of the selective acrolein oxidation. Based on the in situ characterisation in combination with micro kinetic modelling a detailed reaction model which describes the oxygen exchange and the processes at the catalyst more precisely is discussed.

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X-Ray absorption and X-ray diffraction studies on molybdenum doped vanadium pentoxide

Cited by 28 publications

References 9 publications

Structure stabilizing effect of tungsten in mixed molybdenum oxides with Mo5O14-type structure

Structure stabilizing effect of tungsten in mixed molybdenum oxides with Mo5O14-type structure

An in-situ Reduction/Oxidation XAS Study on the EL10V8 VOx/TiO2(Anatase) Powder Catalyst

Heterogeneously catalysed partial oxidation of acrolein to acrylic acid—structure, function and dynamics of the V–Mo–W mixed oxides

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