Structure characterization of orthorhombic phase in MoVTeNbO catalyst by powder X-ray diffraction and XANES

Murayama, Haruno; Vitry, Damien; Ueda, Wataru; Fuchs, G.; Anne, M.; Dubois, Jean‐Luc

doi:10.1016/j.apcata.2006.10.050

Cited by 114 publications

(107 citation statements)

References 21 publications

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“…[9] The complex chemistry of the polycrystalline MoVTeNb oxide catalyst is reflected in its crystal structure. [10][11][12] The model of the M1 unit cell comprises 44 atoms. Metal-oxygen linkages in the polyhedral network give rise to a channel-like structure with 5-sided pillars filled with Nb, and 6-, and 7-sided channels partially occupied by tellurium oxide entities.…”

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

162

183

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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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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

162

183

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“…A highlight in the development process [16][17][18][19][20][21][22] of selective oxidation catalysis was the discovery of the orthorhombic M1 phase MoVNbTeOx. This truly complex mixed oxide This paper is dedicated to Bob Grasselli on the occasion of his 80th birthday.…”

Section: Introductionmentioning

confidence: 99%

“…is a versatile catalyst for several selective oxidation processes of C3 [17,19,[23][24][25][26] and C2 [27,28] feedstock. It works well as crystalline single phase.…”

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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“…Surface and sub-surface reduction and reoxidation of M1 crystals seems to be possible without structural collapse [24]. The occupancy of the 13 metal sites in the unit cell of the crystal structure is variable [9][10]14]. Accordingly, the catalytic properties may be controlled by synthesis or post-treatment procedures.…”

Section: Discussionmentioning

confidence: 99%

“…The M1 structure (ICSD 55097) consists of cornersharing MO 6 octahedrons, (M=Mo,V), which are assembled in the (001) plane forming characteristic hexagonal and heptagonal rings hosting Te-O units. Niobium is preferentially located in pentagonal bipyramidal environment [7][8][9]. However, due to a certain chemical flexibility of the phase, octahedral positions may also be occupied by Nb in M1 with higher Nb content [10].…”

Section: Introductionmentioning

confidence: 99%

How important is the (001) plane of M1 for selective oxidation of propane to acrylic acid?

Sanfiz

Hansen

Sakthivel

et al. 2008

Journal of Catalysis

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The role of the (001) crystallographic plane of the M1 phase of MoVTeNb mixed oxide catalysts in selective oxidation of propane to acrylic acid has been addressed by investigating a phase-pure M1 material preferentially exposing this surface. A model catalyst has been prepared by complete silylation of M1 followed by breakage of the SiO 2 covered needles. Using this approach, the reactivity of the M1 (001) surface has been investigated by combining a micro-reactor study of propane oxidation with High-Sensitivity Low Energy Ion Scattering (HS-LEIS). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been used to study shape and microstructure of the model system and to verify the surface exposure of the model catalyst. The specific formation rate of acrylic acid on the model catalyst is similar to that on the phase-pure M1 reference material indicating that the (001) plane of the M1 crystal structure does not possess enhanced catalytic properties compared to the lateral surface of M1 needles in propane oxidation.

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Structure characterization of orthorhombic phase in MoVTeNbO catalyst by powder X-ray diffraction and XANES

Cited by 114 publications

References 21 publications

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

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

How important is the (001) plane of M1 for selective oxidation of propane to acrylic acid?

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