In this work the solid-state NMR characteristics of unsupported and silica-supported H4[SiMo12O40] and H3[PW12O40] heteropoly acids after (i) calcination or (ii) reaction with 2,3-butanediol are described. The supported and unsupported acids were studied by 29Si or 31P MAS NMR spectroscopy and the supported catalysts, which became steady-state in a 2,3- butanediol flow, were probed by 13C CP MAS NMR measurements as well. The position of Si signal corresponding to the heteropoly acid in H4[SiMo12O40]/SiO2 could be distinguished from the Si signals of the support. The 31P NMR spectrum of H3[PW12O40] 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.
- Si, P and C MAS NMR spectroscopy
- Silica-supported and unsupported heteropoly acids
- Transformations of 2,3-butanediol
ASJC Scopus subject areas
- Analytical Chemistry
- Organic Chemistry
- Inorganic Chemistry