Characterization of tellurium in MoVTeNbO catalysts for propane oxidation or ammoxidation

Millet, J.M.M.; Roussel, Hervé; Pigamo, A.; Dubois, Jean‐Luc; Jumas, Jean‐Claude

doi:10.1016/s0926-860x(02)00078-9

Cited by 168 publications

(146 citation statements)

References 21 publications

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“…The structure of the ternary MoVW oxide is closely related to that of Mo 5 O 14 which shows a complex network of MO 6 octahedra forming slabs that are stacked in such a way that channels are formed [8,19]. The structure of pure Mo 5 O 14 may tolerate additional ions and it has been discussed in the literature that Mo, V or Te ions may partially occupy these channels [30,31]. Considering the Mo-O distances determined by XRD, the channel di- At the same time, NMR spectroscopy deliveres certain hints on the presence of V 5+ ions in an uncommon, maybe highly distorted trigonal pyramidal coordination.…”

Section: Cross-linking By Mo-o-v Bridges Would Also Be In Agreement Withmentioning

confidence: 99%

The structural genesis of a complex (MoVW)5O14 oxide during thermal treatments and its redox behavior at elevated temperatures

Зенковец

Kryukova

Gavrilov

et al. 2007

Materials Chemistry and Physics

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The structural genesis of a Mo 0.68 V 0.23 W 0.09 oxide with Mo 5 O 14 -like structure has been examined.A precursor prepared by spray-drying of mixed aqueous metal salt solutions was calcined in air and subsequently treated in helium at different temperatures. X-ray diffraction, HRTEM, 51 V MAS NMR, ESR, UV/Vis DR spectroscopy and oxygen and hydrogen adsorption measurements have been applied to monitor the preparation procedure. It was found that a structure closely re-

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Section: Cross-linking By Mo-o-v Bridges Would Also Be In Agreement Withmentioning

confidence: 99%

The structural genesis of a complex (MoVW)5O14 oxide during thermal treatments and its redox behavior at elevated temperatures

Зенковец

Kryukova

Gavrilov

et al. 2007

Materials Chemistry and Physics

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“…They open up at the basal plane and have been suggested to be of importance in the reduction and reoxidation of the surface during catalysis. [16,17] Definite occupations of metal framework M1 positions have been proposed to result in the formation of site-isolated active ensembles on its terminating basal plane that are characterized by close proximity of the required catalytic functions, and, consequently, attributed to high selectivity. [18,19] In this respect, vanadyl groups with vanadium at the crystallographic positions M3 and M7 have been considered to be particularly responsible for C-H activation of propane in the rate-determining abstraction of the first hydrogen atom.…”

Section: Introductionmentioning

confidence: 99%

“…This termination model provides a rational explanation for the enriched tellurium content generally observed when surface sensitive methods are applied for analysis of M1. [4,16,[24][25][26][27][28][29] The actual termination may differ depending on local cation site occupancy, [30] synthesis method, pretreatment, and reaction conditions. In conclusion, a thorough characterisation of the M1 phase is required to obtain a detailed understanding of its functionality.…”

Section: Introductionmentioning

confidence: 99%

Surface chemistry of phase-pure M1 MoVTeNb oxide during operation in selective oxidation of propane to acrylic acid

Hävecker

Wrabetz

Kröhnert

et al. 2012

Journal of Catalysis

151

178

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The surface of a highly crystalline MoVTeNb oxide catalyst for selective oxidation of propane to acrylic acid composed of the M1 phase has been studied by infrared spectroscopy, microcalorimetry, and in-situ photoelectron spectroscopy. The acid-base properties of the catalyst have been probed by NH3 adsorption showing mainly Brønsted acidity that is weak with respect to concentration and strength of sites. Adsorption of propane on the activated catalyst reveals the presence of a high number of energetically homogeneous propane adsorption sites, which is evidenced by constant differential heat of propane adsorption qdiff,initial=57 kJ mol -1 until the monolayer coverage is reached that corresponds to a surface density of approximately 3 propane molecules per nm 2 at 313 K. The decrease of the heat to qdiff,initial=40 kJ mol -1 after catalysis implies that the surface is restructured under reaction conditions. The changes have been analyzed with high-pressure in-situ XPS while the catalyst was working applying reaction temperatures between 323 and 693 K, different feed compositions containing 0 mol.-% and 40 mol.-% steam and prolonged reaction times. The catalytic performance during the XPS experiments measured by mass spectrometry is in good agreement with studies in fixed bed reactors at atmospheric pressure demonstrating that the XPS results taken under operation show the relevant active surface state. The experiments confirm that the surface composition of the M1 phase differs significantly from the bulk implying that the catalytically active sites are no part of the M1 crystal structure and occur on all terminating planes. Acrylic acid formation correlates with surface depletion in Mo 6+ and enrichment in V 5+ sites. In presence of steam in the feed, the active ensemble for acrylic acid formation appear to consist of V 5+ oxospecies in close vicinity to Te 4+ sites with an element ratio Te/V=1.4. The active sites are formed under propane oxidation conditions and are embedded in a thin layer enriched in V, Te, and Nb on the surface of the structural stable self-supporting M1 phase.

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“…Although reports exist [23,32] on attempts supported by high-throughput experimentation to improve the function of the M1 phase and to benefit from a suspected synergy [33][34][35] with the related hexagonal M2 [36,37] phase, it is established [38] that a stable and long-term performance can also be achieved with the bare single [39] M1 phase. This gives hope that a detailed understanding of the mode of operation can be obtained based upon accurate oxide crystallography [40] forming the basis of a detailed understanding [41] of the nature of the active site.…”

Section: Introductionmentioning

confidence: 99%

Active Sites for Propane Oxidation: Some Generic Considerations

Schlögl

2011

Top Catal

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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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Characterization of tellurium in MoVTeNbO catalysts for propane oxidation or ammoxidation

Cited by 168 publications

References 21 publications

The structural genesis of a complex (MoVW)5O14 oxide during thermal treatments and its redox behavior at elevated temperatures

The structural genesis of a complex (MoVW)5O14 oxide during thermal treatments and its redox behavior at elevated temperatures

Surface chemistry of phase-pure M1 MoVTeNb oxide during operation in selective oxidation of propane to acrylic acid

Active Sites for Propane Oxidation: Some Generic Considerations

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