On the local structure of Ti during in situ desorption of Ti(OBu)4 and TiCl3 doped NaAlH4

The local structures of Ti doped NaAlH4 were investigated with extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) using Ti(OBu)4 and TiCl3 precursors. The local structures were linked to literature data on hydrogen desorption and absorption kinetics. In the Ti(OBu)4 doped NaAlH4, butoxide or decomposition products thereof (C, O atoms) was bonded to Ti after ball-milling, inhibiting the performance of the Ti catalyst. Upon heating, the C and O atoms were removed and Ti–Al species were formed. The thermodynamical most stable specie, TiAl3, was not formed at T < 300 °C, contrarily to TiCl3 doped NaAlH4. Probably the initially present butoxide group gave rise to inhibition of its formation. Besides that, the butoxide or decompostion products thereof (C, O atoms) are also suspected to interfere with the hydrogen uptake of a desorbed NaAlH4.