Nanoclusters as precursors to (MoVW)₅O₁₄: In situ and chemical characterisation of the systems of a single phase oxidation catalyst

Abstract

The ternary oxide (MoVW) 5 O 14 is considered to be highly significant for catalytic, mild selective oxidation reactions. By using UV/Vis, EPR, 95 Mo NMR spectroscopies and conductivity measurements the coordination chemistry of the molybdate species in the precursor solutions was studied. This work has established that mixing the precursor solutions (ammonium heptamolybdate, ammonium metatungstate and vanadyl oxalate) forms a polymeric network in which the vanadyl species act as a linker between the molybdate species. The addition of tungsten atoms significantly enhances the polymerisation process.

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

“…As it becomes evident from the XRD patterns given in Fig. 4a UV/Vis DR spectroscopy -O-VO 2+ [12]. The other signal with hyperfine splitting arises from isolated VO 2+ ions in octahedral environment [28].…”

“…By spray-drying a mixture of aqueous metal salt solutions followed by thermal activation in air and helium we synthesized a material containing one single (MoVW) 5 O 14 -type phase [11]. The molecular structure comprising of molybdate species linked via vanadyl ions is pre-assembled as a polymeric network already in the mixed precursor solution [12]. In the present paper, the structural transformations were studied occurring during thermal pretreatment of the spray-dried precursor leading to a phase-pure (MoVW) 5 …”

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

“…The structural motif {(M) M 5 } (M = Mo,V,Nb), which is composed of a pentagonal bipyramidal MO 7 unit that shares the five edges of the planar pentagon with five MO 6 octahedra (Scheme 1), is another common feature that is also known as a key constituent of larger structural aggregates that are observed for reduced molybdates in solutions. [6] Icosahedral molecular systems of the type {(Mo VI )Mo 5 VI } 12 (linker) 30 , which are called Keplerates, have been considered as donor of the {(M) M 5 } building blocks in the M 5 O 14 synthesis [7] and the hydrothermal synthesis of Mo 3 VO x , MoVSb, and MoVTeNb mixed oxides with M1 structure. [8] The complexity of the M1 structure provides site isolation, as it is required for a high selectivity in oxidation reactions of C 3 and C 2 feedstock.…”

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

“…14 A similar process of vanadium interaction with Kepplerate ion was described for VMoW oxides with Mo 5 O 14 -like structure. 63,69 Thus, the VMoNb(Te) semi-crystalline oxide can be transformed either into the M1 structure, or into the M2 structure, or into the Mo 5 O 14 -type structure. The nal structure of the polygonal grid is determined by the chemical composition and the thermal treatment conditions.…”