The acidity of niobic acid studied by 1H broad-line NMR at 4 K and H MAS NMR at room temperature: comparison with other solid acids

✍ Scribed by Patrice Batamack; Robert Vincent; Jacques Fraissard

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 848 KB
• Volume: 28
• Category: Article
• ISSN: 0920-5861
• DOI: 10.1016/0920-5861(95)00216-2

✦ Synopsis

The acidity of niobium pentoxide calcined at 573 K has been studied by interacting water molecules and the solid acid using 'H broad-line NMR at 4 K and MAS NMR at room temperature. 'H Broad-line NMR in 'rigid lattice' conditions allows the determination of the numbers of the oxygen-protonated species (H,O+ and Hz0 . . . HO species, unreacted OH groups or excess Hz0 molecules) present when water molecules used as base react with a Brernsted acid. With niobic acid, the method showed a continuous increase in the hydronium ion concentration with the number of water molecules. The ionization coefficient, determined when the ratio of the number of water molecules to that of the acidic hydroxyl groups of niobic acid is one, is 0.2. This value is similar to the ionization coefficients found for some HY zeolites.