Direct and Reversible Synthesis of AlH3−Triethylenediamine from Al and H2

Aluminum hydride, AlH3, is the most well-known alane. Though thermodynamically unstable under ambient conditions, it is easily prepared in a metastable state that will undergo controlled thermal decomposition to produce H2 and Al at around 100 °C. AlH3 contains 10.1 wt % hydrogen and has a density of 1.48 g/mL and is therefore of interest for on-board automotive hydrogen storage. ΔHf and ΔGf298K for α-AlH3 are −9.9 and 48.5 kJ/mol AlH3, respectively. The latter value yields an equilibrium hydrogen fugacity of ∼5 × 105 atm at 298 K, which is equivalent to a hydrogen pressure of ∼7 × 103 atm. Thus, the direct regeneration of AlH3 from spent Al with gaseous H2 is deemed impractical. This paper describes an alternate approach to the regeneration of AlH3 via a low-temperature, low-pressure, reversible reaction using Ti-doped Al powder and triethylenediamine (TEDA). The adduct is formed in a slurry of the Al powder and a solution of TEDA in THF in contact with H2. The AlH3−TEDA product is insoluble and precipit...

[1]  A. Becke.  Density-functional thermochemistry. III. The role of exact exchange , 1993 .

[2]  Jason Graetz,et al.  Decomposition kinetics of the AlH3 polymorphs. , 2005, The journal of physical chemistry. B.

[3]  J. Nimmo,et al.  Solid-state phase transition in triethylenediamine, N(CH2CH2)3N. I. The crystal structure of phase II at 298 K , 1976 .

[4]  M. Fichtner,et al.  Double-Bridge Bonding of Aluminium and Hydrogen in the Crystal Structure of γ-AlH3 , 2007 .

[5]  B. Bogdanovic,et al.  Ti-doped alkali metal aluminium hydrides as potential novel reversible hydrogen storage materials , 1997 .

[6]  J. J. Reilly,et al.  X-ray absorption study of Ti-activated sodium aluminum hydride , 2004, cond-mat/0404363.

[7]  G. Libowitz.  The solid-state chemistry of binary metal hydrides , 1965 .

[8]  E. C. Ashby.  The Direct Synthesis of Amine Alanes , 1964 .

[9]  J. Graetz,et al.  Synthesis and Crystal Structure of -AlD3. , 2007 .

[10]  S. Chaudhuri,et al.  Understanding the role of Ti in reversible hydrogen storage as sodium alanate: a combined experimental and density functional theoretical approach. , 2006, Journal of the American Chemical Society.

[11]  J. W. Turley,et al.  Crystal structure of aluminum hydride , 1969 .

[12]  E. C. Ashby.  Simple and complex metal hydrides of the main group metals. A personal account of the early days , 1980 .

[13]  B. Hauback,et al.  Mechanochemical synthesis and crystal structure of alpha'-AlD3 and alpha-AlD3. , 2006, The journal of physical chemistry. B.

[14]  S. Srinivasan,et al.  Synchrotron X-ray and neutron diffraction studies of NaAlH4 containing Ti additives , 2004 .

[15]  J. R. Johnson,et al.  The kinetics of the absorption of hydrogen by LaNi5Hx-n-undecane suspensions☆ , 1984 .

[16]  J. Graetz,et al.  The Crystal Structure of ?-AlD3. , 2007 .

[17]  D. R. Stull,et al.  Thermodynamic Properties of Aluminum Hydride , 1967 .

[18]  C. B. Roberts,et al.  Preparation and properties of aluminum hydride , 1976 .

[19]  J. Reilly,et al.  Hydrogenation of 1-Octene Using α/β LaNi5Hx as a Catalyst* , 1994 .

[20]  J. Graetz,et al.  Thermodynamics of the a , and ? polymorphs of AlH 3 , 2006 .

[21]  Parr,et al.  Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. , 1988, Physical review. B, Condensed matter.

[22]  Santanu Chaudhuri,et al.  First-principles study of Ti-catalyzed hydrogen chemisorption on an Al surface: a critical first step for reversible hydrogen storage in NaAlH4. , 2005, The journal of physical chemistry. B.

[23]  H. Schlesinger,et al.  Lithium Aluminum Hydride, Aluminum Hydride and Lithium Gallium Hydride, and Some of their Applications in Organic and Inorganic Chemistry1 , 1947 .

[24]  C. Ciobanu,et al.  Short-range order of low-coverage Ti∕Al(111): Implications for hydrogen storage in complex metal hydrides , 2007 .