Characterization of ti Catalyst in NaAlH4 Doped with TiF3
Abstract
The discovery that the dehydrogenation and rehydrogenation of NaAlH4 can be catalyzed by addition of titanium-based compounds has catapulted complex hydrides such as NaAlH4 to the forefront of hydride research. However, the nature of the titanium catalyst has remained controversial as only circumstantial evidence of its oxidation state, bonding environment and catalytic mechanism have been reported thus far. Results of detailed in-situ powder x-ray diffraction experiments on both the dehydrogenation and the rehydrogenation reactions of NaAlH4 will be presented. These novel data prove that both reactions occur in a stepwise fashion and agree well with pressure-composition isotherms of the same material. Furthermore, peak width analysis yields information about some surprising changes in the particle size of the constituent phases during the reaction and with cycling. X-ray absorption fine structure analysis (XANES/EXAFS) at the temperatures of interest reveals the oxidation state of the titanium species after synthesis and upon cycling. The local coordination environment of the titanium yields clues regarding possible catalytic mechanisms.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2004
- Bibcode:
- 2004APS..MARS39011R