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

Зенковец, Г. А.; Kryukova, G. N.; Gavrilov, V. Yu.; Tsybulya, S. V.; Anufrienko, V.A.; Larina, T. V.; Khabibulin, Dzhalil F.; Lapina, Olga B.; Rödel, Eva; Trunschke, Annette; Ressler, Thorsten; Schlögl, Robert

doi:10.1016/j.matchemphys.2007.02.029

Cited by 13 publications

(11 citation statements)

References 28 publications

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“…Silica or alumina are thus no optimal supports for partial oxidation catalysts but molybdenum oxide (in the form of the M1 phase) or other reducible mixed oxides with a stable geometric structure [65][66][67][68][69][70][71][72] are suitable choices for reactions involving both C-H activation and oxygen transfer. The in situ analytical results described above and the concept of site isolation preclude, however, the view that a reactive dimer ''antenna site'' may be connected to the bulk of the M1 phase acting as collective electron storage unit.…”

Section: Size and Functions Of Active Sitesmentioning

confidence: 99%

Active Sites for Propane Oxidation: Some Generic Considerations

Schlögl

2011

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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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Section: Size and Functions Of Active Sitesmentioning

confidence: 99%

Active Sites for Propane Oxidation: Some Generic Considerations

Schlögl

2011

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“…In its pure form, the M2 phase is efficient in the conversion of propylene to the same products (11, 13, 22) by selective oxidation and ammoxidation. Using propane as a feedstock, the composite M1/M2 system catalyzes the production of acrylonitrile with yields up to 62% (23) and in the case of the synthesis of acrylic acid at yields up to 53% for selective oxidation (24).Following the initial studies, significant effort has been focused on improvement of this system through elemental substitutions or the development of new structural variants (8,18,(25)(26)(27)(28)(29). Compositional variants of the M1 phase have been successfully prepared ranging from the simplest two component Mo-V-O case to more complex formulations that commonly incorporate combinations of Te, Sb, Nb, and/or Ta (8,18,[25][26][27][28][29].…”

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“…Compositional variants of the M1 phase have been successfully prepared ranging from the simplest two component Mo-V-O case to more complex formulations that commonly incorporate combinations of Te, Sb, Nb, and/or Ta (8,18,[25][26][27][28][29]. 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.…”

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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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“…This strength is given by the nature of the central cation in each of the octahedra forming the perimeter of the rosette feature. The variable cation distribution 473 that gives an ordered form rise to the features of Figure 44 occurs without long-range order in each of the rosettes and determines in this way if Mo−O or V−O is the terminating surface species. It was found 471 that the working catalyst is enriched in V x O y species relative to the bulk concentration within the standard unit cell: the structural origin is the more facile breaking of less-stable VO 6 structures than MoO 6 structures.…”

Section: Structure Of Complex Oxide Catalystmentioning

confidence: 99%