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Werner, Harald; Timpe, Olaf; Herein, Daniel; Uchida, Yuji; Pfänder, Norbert; Wild, Ute; Schlögl, Robert; Hibst, H.

doi:10.1023/a:1018901830923

Cited by 68 publications

(47 citation statements)

References 14 publications

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“…The data at 382 1C show only a very slight decrease in oxidation state from 5.6 to 5.3, coupled with small structural changes around the Mo centres. This is compatible with the proposals of Andrushkevich 14 and Schlo¨gl et al 15,16 for possible active phases in the catalyst. At temperatures above 400 1C, the change of oxidation state is much more drastic, and average minimum oxidation states close to Mo 4+ are reached.…”

Section: Reductive Conditionssupporting

confidence: 93%

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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Section: Reductive Conditionssupporting

confidence: 93%

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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“…These findings must be related to the same system where θ-(VNbMo) 5 O 14 and MoO 3 , are present, their crystalline state being mainly related to their catalytic activity. Werner et al [30] have emphasized the role of the 'glassy nanocrystalline state' of such material in catalysis. On the contrary, if crystals of MoO 3 are too large, and because they naturally exhibit mostly {010} faces, the production of CO x is high [53].…”

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

“…Multicomponent catalysts have flourished recently because of the versatility of the MoV system which accommodates several types of dopant, such as catalysts for mild oxidation of propane to acrylic acid [27][28][29][30][31][32]. If tungsten is generally preferred to Nb for these reactions, the Mo 5 O 14 -type oxide is often present in the system as detected by XRD and Raman spectroscopy [20,[30][31][32][33][34], and as such it may be a key factor to relate to catalytic properties. However, the structure of other phases present in the MoVXYO system and which are related with the presence of dopants X, Y, has been recently solved [35][36][37][38][39][40][41][42] and their presence could make the difference with the MoVNbO system more active for ethane oxidation.…”

mentioning

confidence: 99%

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Oxidation of ethane to ethylene and acetic acid by MoVNbO catalysts

et al. 2005

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“…The active surface requires defects in its oxygen-terminated surface [14,15] for exposing metal sites to the reaction environment [16]. An array of oxoclusters linked by small metal-oxopolyhedra could provide the transfer function for ions with low activation barriers [17][18][19][20] but requires a specific support structure to survive its dynamical rearrangement during catalytic operation. Led by this vision [21], crystalline Mo-V-Te-Nb oxide was optimized to function as support and as reservoir for the formation and stabilization of an active network of oxoclusters on the surface of the crystallites.…”

Section: Introductionmentioning

confidence: 99%

Surface texturing of Mo–V–Te–Nb–O x selective oxidation catalysts

et al. 2006

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The paper concentrates on the study of Mo-V-Te-Nb oxide mixtures by electron microscopy combined with catalytic investigation of these materials in the partial oxidation of propane. Surface texturing of catalyst particles composed of two phases referred to in the literature as M1 and M2 is revealed by high-resolution transmission electron microscopy of high performing catalysts. The chemical composition of the catalyst surface is modified by treatment in water to obtain a significant increment in yield of acrylic acid. A chemical realization of the site isolation concept recurring on a supramolecular arrangement of catalyst and reactant rather than on atomic site isolation is suggested. A complex Mo-V-Te-Nb-Ox precursor phase carries nanoparticles made from a network of oxoclusters active as catalyst for the conversion of propane to acrylic acid. The designed synthesis of the multielement oxide bulk and of the surface structure with a different composition than the precursor phase improved the performance by a factor of 4.

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Untitled

Cited by 68 publications

References 14 publications

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

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

Oxidation of ethane to ethylene and acetic acid by MoVNbO catalysts

Surface texturing of Mo–V–Te–Nb–O x selective oxidation catalysts

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