Development of the local and average structure of a V–Mo–Nb oxide catalyst with Mo₅O₁₄-like structure during synthesis from nanostructured precursors

Abstract

A combination of X-ray and neutron PDF measurements with powder diffraction and EXAFS data was used to determine the structures of a V--Mo--Nboxide catalyst and its poorly crystallized precursors that exhibit the strongest catalytic activities. The crystalline material belongs to space group P42 1 m, a ¼ 22.8, c ¼ 4.002, and is build up of pentagonal MeO 7 bipyramids surrounded by edge sharing Me-octahedrons (Me ¼ Mo, V, Nb). In the average structure all MeO 7 units are at the same z-level, while the local structure analysis shows systematic shifts along [001]. Samples synthesized at 300 C and 400 C exhibit a nanostructure, whose local structure predates the final crystalline structure. Initial nanoparticles are spherical and grow predominantly along the c-axis. The successful analysis required a reverse analysis that took the crystalline material as starting model for the samples synthesized at lower temperatures.

The evolution of the M1 local structure during preparation of VMoNbTeO catalysts for ethane oxidative dehydrogenation to ethylene

“…The observed features of the local structure are similar to those previously reported by our group in ref. 58 , where the development of the Mo 5 O 14 -like local structure was studied in the three-component VMoNb system.…”

“…According to our previous findings, only Mo 5 O 14 -type of the structure with pentagonal domains is formed in the V 0.3 Mo 1 Nb 0.37 oxide system. 58 The addition of Te in the mixed oxide causes the formation of the M1 phase. However, the local structure of the semi-crystalline VMoNb and VMoNbTe oxides is similar.…”

“…The observed features of the local structure are similar to those previously reported by our group in ref. 58, where the development of the Mo 5 O 14 -like local structure was studied in the three-component VMoNb system. To simulate the structure of a semi-crystalline VMoNb oxide, a model based on the pentagonal domain was developed.…”

“…The similar pentagonal domains were found as a main structural feature of semi-crystalline oxide phases in the VMoTe and VMoNb oxide systems. 58,59 However, despite the structural similarity of the semi-crystalline phases in these systems, the phase composition aer crystallization is different. In the V 0.3 Mo 1 Te 0.23 oxide system, M2 phase and (Mo, V) 5 O 14 phases are formed, 59 while the calcination of the semi-crystalline V 0.3 Mo 1 Nb 0.37 precursor results in the appearance of the (Mo, V, Nb) 5 O 14 mixed oxide.…”

Enhanced Lithium Storage in Micrometer‐Scale Tungsten Bronze Mo3Nb2O14 by Molybdenum Reduction and Oxygen Deficiency

“…technologically important properties in various areas including nonlinear optics, [16] wave filters, dielectric resonators, [17] optical waveguides, [18] light modulators, infrared detectors, [19] ferroelectrics, [20] catalysis, [21] and rechargeable batteries. [22] Among the tungsten bronze structures, tetragonal tungsten bronzes (TTBs) are the most common structures.…”