Mo5O14 – twinning and three-dimensional structure, determined from a partly tantalum-substituted crystal

Yamazoe, Noboru; Kihlborg, L. H. E.

doi:10.1107/s0567740875005882

Cited by 42 publications

(47 citation statements)

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“…Alternatively, several other Mo-V-O-based phases related to the M1 catalyst have been identified and are comprised of similar structural units, involving common pentagonal Mo building blocks fMo 6 O 21 g which consist of five fMoO 6 g octahedra that each share one edge with a fMoO 7 g pentagonal bipyramidal center. These structurally related materials are either pseudotetragonal and similar to the well-known Mo 5 O 14 -type structure originally reported by Kihlborg et al, or a recently discovered phase with trigonal symmetry (27,30,31). Fig.…”

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confidence: 99%

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Atomic-level imaging of Mo-V-O complex oxide phase intergrowth, grain boundaries, and defects using HAADF-STEM

Pyrz

Blom

Sadakane

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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In this work, we structurally characterize defects, grain boundaries, and intergrowth phases observed in various Mo-V-O materials using aberration-corrected high-angle annular dark-field (HAADF) imaging within a scanning transmission electron microscope (STEM). Atomic-level imaging of these preparations clearly shows domains of the orthorhombic M1-type phase intergrown with the trigonal phase. Idealized models based on HAADF imaging indicate that atomic-scale registry at the domain boundaries can be seamless with several possible trigonal and M1-type unit cell orientation relationships. The alignment of two trigonal domains separated by an M1-type domain or vice versa can be predicted by identifying the number of rows/columns of parallel symmetry operators. Intergrowths of the M1 catalyst with the M2 phase or with the Mo 5 O 14 -type phase have not been observed. The resolution enhancements provided by aberration-correction have provided new insights to the understanding of phase equilibria of complex Mo-V-O materials. This study exemplifies the utility of STEM for the characterization of local structure at crystalline phase boundaries.propane | oxidation | catalyst | acrylonitrile | bronze S elective catalytic oxidation of light hydrocarbons is of tremendous commercial importance for the production of a variety of key industrial organic chemicals and intermediates. Existing processes, valued in the billions of US dollars per annum, are predominantly based on oxidation of olefin feeds; however, there are significant economic and environmental benefits to replacement by more energy-and carbon-efficient paraffin-fed processes. Pursuit of active and selective catalysts for use in such replacement processes is a currently very active area of research. Mixed-metal oxides in the system Mo-V-Nb-Te-O, when prepared under mildly reducing conditions, may consist of one or more of several network "bronze" structures with mixed valences for Mo and V (1-4). Materials from this system show promise as catalysts for selective oxidation of ethane to ethylene, propane to acrylic acid, and, in the presence of cofed ammonia, propane ammoxidation to acrylonitrile. One phase in particular, commonly designated as "M1," has been found to be essential as a catalyst component for selective paraffin oxidation, and under some conditions seems to be promoted by coexistence with another phase designated as "M2" (1-18). Our interest in chemical and structural inhomogeneities observed in this system is driven by the apparent need for composite M1/M2 phase coexistence to realize the most active, selective, and stable catalysts.The M1 phase has an orthorhombic unit cell with a structure comprised of a network of interconnected pentagonal fMo 6 O 21 g rings joined together by linking octahedra, resulting in the formation of nanoscale hexagonal and heptagonal channels (4,14,(19)(20)(21). The M2 phase is belongs to the hexagonal tungsten bronze family, but exhibits a small orthorhombic distortion (4). In its pure form, the M2 phase is efficient in ...

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“…The intergrowths observed in this study are unique examples of lattice registry in this important complex oxide bronze family. (30). For the trigonal phase, we have adopted the model proposed earlier by Sadakane et al based on the analysis of powder x-ray diffraction data (27).…”

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confidence: 99%

Atomic-level imaging of Mo-V-O complex oxide phase intergrowth, grain boundaries, and defects using HAADF-STEM

Pyrz

Blom

Sadakane

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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“…Mo 5 O 14 tolerates the incorporation of considerable amounts of V and W. Stoichiometries of such phases were reported to be (Mo 0.92 V 0.08 ) O 14 or (Mo 0.75 W 0.25 )O 14 , respectively [23]. Especially, the incorporation of W favors the formation of Mo 5 O 14 -type oxides comparable with the results on Ta and Nb incorporation [24,25]. Tungsten and vanadium, thus, act as structural promoters enhancing, and stabilizing the formation of the Mo 5 O 14 -type phase.…”

Section: Characterization Of Catalystmentioning

confidence: 51%

Synthesis and characterization of nanocrystalline Mo–V–W–Fe–O mixed oxide catalyst and its performance in selective methanol oxidation

2007

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A mixed oxide catalyst containing Mo, V, W and Fe with the composition of 63, 23, 09 and 06 wt% respectively for the selective oxidation of the methanol to formaldehyde is in reported in this paper for the first time. The characterization of the catalyst was done using BET surface analysis, X-ray diffraction (XRD), Infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and Energy dispersive X-ray (EDX). The mixed oxide after calcination at 673 K in N 2 which was subjected for the thermal activation in N 2 flow at 813 K was used for the methanol selective oxidation. The thermal treatment shows enhanced catalytic performance. Thermal activation of the nanocrystalline Mo 0.63 V 23 W 0.09 Fe 0 . 06 O x precursor oxide in nitrogen atmospheres induces partial crystallization of a Mo 5 O 14 -type oxide only in a narrow temperature range up to 813 K. XRD showed that the thermally activated mixed oxide consists of a mixture of a majority of crystalline Mo 5 O 14 -type oxide and of small amounts of crystalline MoO 3 -type and MoO 2 -type oxides. The structural analysis suggests that the improvement of the catalytic performance of the MoVWFe oxide catalyst in the selective oxidation of methanol is related to the formation of the catalytic active site such as Mo 5 O 14 -type mixed oxide.

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“…MoO 2 was detected in trace amounts by XRD too. The second [33,34], which explains the detection of MoO 3 -and MoO 2 -type oxides.…”

Section: Catalytic Results and Xrd Characterisationmentioning

confidence: 98%

MoVW mixed metal oxides catalysts for acrylic acid production: from industrial catalysts to model studies

Mestl¹

2006

Top Catal

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MoVW) 5 O 14 -type oxides were identified as the active and selective components in industrial acrylic acid catalysts. Tungsten is suggested to play an important role as a structural promoter in the formation and stabilization of this oxide. Vanadium is responsible for high catalytic activities but is detrimental for the stability of this oxide at the necessary high concentrations for optimum catalytic performance. The activity of mixed MoVW oxide catalysts for methanol, propene, and acrolein partial oxidation could be considerably improved, when the amount of the (MoVW) 5 O 14 -type oxide was increased by thermal annealing. A model is proposed on the basis of the correlation between Raman wavenumber and bond order and degree of reduction, which explains the observed different selectivities of MoO 3)x and the (MoVW) 5 O 14 -type oxides in terms of metal-oxygen bond strengths, i.e. oxygen basicity and oxygen lability, respectively. According to this model, the (MoVW) 5 O 14 mixed oxide catalyses partial oxidation because of its intermediate C-H activation and oxygen releasing oxygen functionalities. However, these (MoVW) 5 O 14 -type industrial oxidation catalysts are heterogeneous and highly complex systems. Their physicochemical characterization also revealed that their chemical bulk and surface compositions vary with thermal activation and oxygen potential. A core-shell model is suggested to describe the active catalyst state, the shell providing a high number of active centers, the core high electronic conductivity and ion mobility. The fact that the surface composition of such catalysts is considerably different from their bulk compositions, most probably implies that the ''molecular structure'' at their surface differs too considerably from their bulk crystal structure. Hence, the posed question about the active catalyst structure and its relation to its catalytic performance cannot unambiguously be explained by the crystallographic structure, but still remains unsolved.

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Mo5O14 – twinning and three-dimensional structure, determined from a partly tantalum-substituted crystal

Cited by 42 publications

References 4 publications

Atomic-level imaging of Mo-V-O complex oxide phase intergrowth, grain boundaries, and defects using HAADF-STEM

Atomic-level imaging of Mo-V-O complex oxide phase intergrowth, grain boundaries, and defects using HAADF-STEM

Synthesis and characterization of nanocrystalline Mo–V–W–Fe–O mixed oxide catalyst and its performance in selective methanol oxidation

MoVW mixed metal oxides catalysts for acrylic acid production: from industrial catalysts to model studies

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