Multinuclear MAS NMR characterization of heteropoly acids and their interaction with 2,3-butanediol

Török, B. and Pálinkó, István and Molnár, Árpád and Rózsa-Tarjáni, M. (1999) Multinuclear MAS NMR characterization of heteropoly acids and their interaction with 2,3-butanediol. JOURNAL OF MOLECULAR STRUCTURE, 482-48. pp. 329-332. ISSN 0022-2860

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Abstract

Zn this work the solid-state NMR characteristics of unsupported and silica-supported H(4)[SiMo(12)O(40)] and H(3)[PW(12)O(40)] heteropoly acids after (i) calcination or (ii) reaction with 2,3-butanediol are described. The supported and unsupported acids were studied by (29)Si or (31)P MAS NMR spectroscopy and the supported catalysts, which became steady-state in a 2,3-butanediol flow, were probed by (13)C CP MAS NMR measurements as well. The position of Si signal corresponding to the heteropoly acid in H(4)[SiMo(12)O(40)]/SiO(2) could be distinguished from the Si signals of the support. The (31)P NMR spectrum of H(3)[PW(12)O(40)] revealed that the material contains two species: one is somewhat dehydroxylated, but fully protonated, the other is further dehydrated and probably proton deficient too. Deposition onto silica stabilized the fully protonated form. Upon contact with 2,3-butanediol proton transfer also occurred. The chemical reactions were identified as dehydration with the loss of one water molecule followed by rearrangement or with simple loss of two water molecules. The steady-state catalysts contained the irreversibly adsorbed reactant, the 2,3-butanediol. However, it was not catalyst poison, but essential constituent of the working catalyst.

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