Chemical State and Local Structure around Titanium Atoms in NaAlH₄ Doped with TiCl₃ Using X-ray Absorption Spectroscopy

Abstract

X-ray absorption spectroscopy is applied to investigate NaAlH 4 doped with 5 mol % TiCl 3 by ball milling. XANES analysis indicates that after the ball milling Ti species are reduced from Ti (+3) to Ti (0). Release or absorption of hydrogen does not affect the chemical state obtained after ball milling. EXAFS analysis shows that the Ti atoms are associated only with Ti as next neighbors in the ball-milled state as well as during subsequent desorption and absorption of hydrogen. Furthermore, an increase of the particle size and an ordering of the local structure is seen to evolve with the desorption and the absorption of hydrogen.

Hydrogen Dynamics in Lightweight Tetrahydroborates

“…Interestingly, the sorption reaction is only reversible under technically applicable conditions, if the material is doped with transition-metal compounds, most efficiently with titanium compounds [68][69][70]. A multitude of experimental and theoretical methods have been applied to unravel the mechanism of the formation and decomposition process of NaAlH 4 -so far without a conclusive model [71][72][73][74][75][76][77][78][79][80][81]. Furthermore, similar effective additives for other complex hydrides e.g.…”

XAS and XES Techniques Shed Light on the Dark Side of Ziegler–Natta Catalysts: Active‐Site Generation

“…In particular, a sharp feature is observed at 4980 eV (having a shoulder at 4977 eV), which was assigned to allowed Ti(1s) → Cl(4p) transitions, enhanced by the multiple scattering contributions characteristic of well crystalline materials. [32,33,42] These features are absent in the XANES spectrum of the catalyst, suggesting that the multiple scattering contributions are limited. This observation is again in favor of a lowdimensional TiClx phase.…”

Vacancy mediated desorption of hydrogen from a sodium alanate surface: An ab initio spin-polarized study

“…Since then, substantial progress has been made experimentally in studying the kinetics of Ti-doped sodium alanate for both the hydrogenation and dehydrogenation processes. 13,14 Currently, it is believed that the final oxidation state of the titanium is zero, 15,16 which is independent of the initial oxidation state and how Ti is added to NaAlH 4 . However, there is still a continuing experimental controversy on precisely where the Ti resides and the exact role of the catalyst.…”