NMR Spectroscopic Studies of Interactions in Solution during the Synthesis of MoVTeNb Oxide Catalysts

• Published in: European Journal of Inorganic Chemistry Vol. 2008; no. 31; pp. 4906 - 4914
• Main Authors: Maksimovskaya, Raisa I., Bondareva, Valentina M., Aleshina, Galina I.
• Format: Book Review Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.11.2008; WILEY‐VCH Verlag
• Subjects: Molybdenum; NMR spectroscopy; Polyoxometalates; Tellurium; Vanadium
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.200800500

Aqueous solutions used for the synthesis of MoVTeNb oxide catalysts have been studied with 125Te, 95Mo, 51V, and 17O NMR spectroscopy. Polyoxometalate (POM) anion V9TeO285– (I), which has the decavanadate structure, containing Te6+ in one of its two central positions, has been identified for the first time in VV‐TeVI solutions. In ternary MoVI‐VV‐TeVI solutions, the POMs TeMo6O246– (II) (pH ca. 7.8–2) as well as previously unknown complexes of the proposed compositions TeV3Mo3O249– (III) (pH ca. 8–5) and TeMo3V5O275– (IV) (pH ca. 6–1) were observed. In the structure of IV, half of the decavanadate anion is combined with half of the octamolybdate anion, in which the central Mo atom is replaced with Te6+. There is an equilibrium, IV [rlarr2] I + II, in the ternary solutions. Despite its stability in solution, polyanion IV could not be isolated in the solid state. During concentration under ambient conditions, less soluble polyanion II begins to crystallize first, and the equilibrium in solution gradually shifts to I. Upon dissolving the precipitate, complex IV forms again. The distribution diagrams have been derived from the NMR spectra for a solution of the cationic composition Mo1V0.3Te0.23 with NH4+ as a counterion, acidified with HClO4 in the pH range 7.25–1. In addition to the above‐mentioned complexes, VO2+ and MoO22+ oxalates form in the presence of oxalic acid. Upon adding niobium oxalate, Nb2O5 gel forms without any Nb‐containing species in solution. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) Three novel polyoxometalate anions, V9TeO285– (I), V3Mo3O249– (III), and V5Mo3TeO275– (IV), have been observed, in addition to TeMo6O246– (II), in aqueous MoVI‐VV‐TeVI solutions in the pH range 8–1, by using 51V, 95Mo, 17O, and 125Te NMR spectroscopy. Upon adding Nb oxalate, the Mo and V oxalates also form.