Structure stabilizing effect of tungsten in mixed molybdenum oxides with Mo5O14-type structure

Abstract

Bulk structural properties of single phase crystalline (Mo 0.91 V 0.09 ) 5 O 14 and (Mo 0.68 V 0.23 W 0.09 ) 5 O 14 materials were investigated using in situ X-ray diffraction and in situ X-ray absorption spectroscopy at three metal edges. Temperature programmed experiments in reducing (propene) and oxidizing (oxygen) atmosphere and isothermal redox experiments at 773 K revealed differences in the bulk properties of the two phases studied. A structure stabilizing effect of tungsten in (MoVW) 5 O 14 under oxidizing conditions was found. Moreover, tungsten centers in a (MoVW) dioxide material exert a structure-directing effect towards re-oxidation to a Mo 5 O 14 -type structure.

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

“…The catalytic activity is well established for semi-crystalline Mo 5 O 14 -type V--Mo--W oxidic compositions that are the major component of V--Mo--W based industrial catalysts for acrolein oxidation to acrylic acid [28][29][30]. According to literature data [30,31] the monophasic semi-crystalline samples are characterized by the very specific powder diffraction pattern that consists of diffuse maxima and a sharp reflection at 4.0 Å .…”

Promoted Hexagonal Tungsten Bronzes as Selective Catalysts in the Aerobic Transformation of Alcohols: Glycerol and Methanol

“…This is the case of Mo-based materials presenting tetragonal Mo5O14 [7,8], tetragonal tungsten bronze (TTB) [9] or the MoV-based orthorhombic structure, the so-called M1 phase [1,4,13]. In all of these cases, the partial substitution of Mo by other transition metals such as V, W or Nb, strongly improves their catalytic behavior in the partial oxidation of acrolein to acrylic acid [7,8], olefins to aldehydes and acids [9], (amm)oxidation of propane to acrylonitrile and acrylic acid [1, 4, 10-12], or in the oxidative dehydrogenation of ethane to ethylene [13].…”

“…In the case of molybdenum oxide-based bronzes, the isomorphous incorporation of other elements such as V, W or Nb, modifies the physical-chemical and catalytic properties, and in some cases the thermal stability [7][8][9][10][11][12][13]. This is the case of Mo-based materials presenting tetragonal Mo5O14 [7,8], tetragonal tungsten bronze (TTB) [9] or the MoV-based orthorhombic structure, the so-called M1 phase [1,4,13].…”

“…They can be ternary compounds of the type AxMyOz in which M is a transition metal (Mo, W, V, Nb, Ta, Ti, ..) and A is an alkali, alkaline earth or NH4 + ion [5,6], and seem to be of interest as catalysts and photocatalysts [7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

Mechanistic Study on the Selective Oxidation of Acrolein to Acrylic Acid: Identification of the Rate‐Limiting Step via Perdeuterated Acrolein

“…Hence, tungsten does not participate in redox processes and acts as a structural promoter. Higher thermal and long‐term stabilities, as well as higher AA yields, are gained by adding tungsten …”