Deuterium Solid-State NMR Study of the Dynamic Behavior of Deuterons and Water Molecules in Solid D3PW12O40

• Published in: The journal of physical chemistry. B Vol. 107; no. 45; pp. 12438 - 12443
• Main Authors: Stepanov, Alexander G, Shegai, Timur O, Luzgin, Mikhail V, Essayem, Nadine, Jobic, Hervé
• Format: Journal Article
• Language: English
• Published: American Chemical Society 13-11-2003
• Subjects: Catalysis; Chemical Sciences
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp030204c

The mobility of water molecules and deuterons of the deuterated analogue of solid 12-tungstophosphoric acid, H3PW12O40·nH2O (HPA) (n = 5.5 and 0.1), has been characterized by deuterium solid-state NMR. Analysis of the 2H NMR line shape and spin−lattice relaxation times allowed us to characterize the deuteron and water dynamics in HPA, at different water contents, in the temperature range 103−383 K. At 163−193 K and for n = 5.5, an intramolecular motion corresponding to reorientations by 180° flips around the C 2 axis of water in the [D5O2]+ ion has been detected, the deuteron being probably immobile. At temperatures above 313 K, both water and deuteron become involved in fast rotation around the C 3 axis of the formed [D3O]+ ion. The rotation is performed on a time scale of 30−50 ns with an activation energy E a of 8.5 kJ/mol. For n = 0.1, three dynamically different species can be distinguished:  mobile deuterons, mobile [D3O]+ ions, and immobile deuterons. Mobile deuterons are weakly bonded to polyanions and move fast with a characteristic time of a few picoseconds and E a = 8.6 kJ/mol. [D3O]+ ions move more slowly than deuterons, but still fast, with a time scale of a few nanoseconds, and E a = 17.6 kJ/mol. The characteristic time for immobile deuterons is much greater than a few microseconds.