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NMR Spectroscopic Studies of Interactions in Solution during the Synthesis of MoVTeNb Oxide Catalysts
Author(s) -
Maksimovskaya Raisa I.,
Bondareva Valentina M.,
Aleshina Galina I.
Publication year - 2008
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200800500
Subject(s) - chemistry , aqueous solution , polyoxometalate , counterion , cationic polymerization , inorganic chemistry , dissolution , ternary operation , catalysis , nuclear magnetic resonance spectroscopy , crystallography , oxide , nmr spectra database , ion , stereochemistry , spectral line , polymer chemistry , organic chemistry , physics , astronomy , programming language , computer science
Aqueous solutions used for the synthesis of MoVTeNb oxide catalysts have been studied with 125 Te, 95 Mo, 51 V, and 17 O NMR spectroscopy. Polyoxometalate (POM) anion V 9 TeO 28 5– ( I ), which has the decavanadate structure, containing Te 6+ in one of its two central positions, has been identified for the first time in V V ‐Te VI solutions. In ternary Mo VI ‐V V ‐Te VI solutions, the POMs TeMo 6 O 24 6– ( II ) (pH ca. 7.8–2) as well as previously unknown complexes of the proposed compositions TeV 3 Mo 3 O 24 9– ( III ) (pH ca. 8–5) and TeMo 3 V 5 O 27 5– ( 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 Te 6+ . 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 Mo 1 V 0.3 Te 0.23 with NH 4 + as a counterion, acidified with HClO 4 in the pH range 7.25–1. In addition to the above‐mentioned complexes, VO 2 + and MoO 2 2+ oxalates form in the presence of oxalic acid. Upon adding niobium oxalate, Nb 2 O 5 gel forms without any Nb‐containing species in solution. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)