Aiding the Self‐Assembly of Supramolecular Polyoxometalates under Hydrothermal Conditions To Give Precursors of Complex Functional Oxides

Abstract

n situ Raman spectroscopy allows insight into molecular processes under hydrothermal conditions during synthesis of complex nanostructured MoVTeNb oxides (see picture: Nb yellow, Mo blue, V/Mo pale blue, Te red). Based on the knowledge acquired, the synthesis can be more efficiently directed towards the desired product with improved functionality

Capsules with Highly Active Pores and Interiors: Versatile Platforms at the Nanoscale

“…The {Mo 132 }‐type capsules can even be used for the synthesis of metal oxides, for example, Mo‐V‐Sb30 (Figure 2) and Mo‐V‐Te29a oxides, thereby also demonstrating the transferability of pentagonal {(Mo VI )Mo VI 5 }‐type units as well as their role in the controlled syntheses of complex multielement oxide phases, which are of great importance as catalysts for the selective oxidation of light alkanes 53a. It should be noted that the smaller Keplerates with mononuclear linkers43, 44a act similarly as they exhibit the same pentagonal units 53b. 54…”

Self-Organized Transformation from Hexagonal to Orthorhombic Bronze of Cs–Nb–W–O Mixed Oxides Prepared Hydrothermally

“…At this point, it is important to recall that the need of species allocated in the hexagonal and/or heptagonal tunnels in order to stabilize the M1 phase is a well-established fact. [11][12][13][14][15][16] The schematic representation of Figure 9a…”

“…In particular, their highly anisotropic transport properties, [2][3][4][5]7 are of interest in applications such as electrochromic devices, batteries, solar cells, sensors or electrocatalysts. 1, 2, 7-10 More recently, they have been used as efficient catalysts as well, [10][11][12][13][14][15][16] especially those corresponding to the so-called M1 phase, with orthorhombic symmetry and nanoscale 5-, 6-and 7-fold channels, [11][12][13][14][15][16] which are very selective catalysts in the oxidation and ammoxidation of propane [10][11][12][13][14][15] and in the oxidative dehydrogenation of ethane to ethylene. 16 In the Mo-V-Te-Nb-O system, the M1 phase forms a multiple active catalyst together with the so-called M2 phase (a pseudohexagonal bronze), among which a synergistic effect has been proposed that is still the subject of controversy.…”

“…20,[28][29][30] Various preparation methods have been reported to obtain Mo-containing M1type -materials and it has been always challenging to prepare it as a single phase. [11][12][13][14][15][16][31][32][33][34] These procedures include precipitation-evaporation, hydrothermal or reflux and the as prepared amorphous materials must be heat-treated at ca. 600ºC under inert atmosphere to obtain the desired M1 crystal phase.…”

“…At this point it is important to mention that diffraction patterns of samples, A-600, D-600 and E-600 are imprecise so they are compatible with those obtained for M1 in Mo-V based materials in the early stages of crystallization. [12][13][14][15][16] After treatment at 1000º C, sample C does not change significantly and C-1000 is fully indexed on the basis of the unit cell of Cs0.2W0.8Nb0.2O3 HTB-type structure(Figure 1c). Diffraction pattern of A-1000 can also be indexed on the basis of the HTBtype structure.…”