Investigation of LiAlH4–THF formation by direct hydrogenation of catalyzed Al and LiH

Abstract

The formation of LiAlH(4)-THF by direct hydrogenation of Al and LiH in tetrahydrofuran (THF) was investigated using spectroscopic and computational methods. The molecular structures and free energies of the various possible adducts (THF-AlH(3), THF-LiH and THF-LiAlH(4)) present in a LiAlH(4)/THF solution were calculated and the dominant species were determined to be contact ion pairs where three THF molecules coordinate the lithium. Raman and X-ray absorption spectroscopy were used to investigate the effect of different Ti precursors on the formation of Al-H species and LiAlH(4)-THF and determine the optimal reaction conditions. A unique sample stage was developed from a microfluidic cell to evaluate the catalysts in situ. The effectiveness of two types of catalysts, titanium chloride (TiCl(3)) and titanium butoxide (Ti(C(4)H(9)O)(4)), and the catalyst concentration were evaluated under similar reaction conditions. Both catalysts were effective at facilitating hydrogenation, although TiCl(3) was more effective over the first few cycles with the greatest kinetic enhancement achieved with a low concentration of around 0.15 mol%. These results were qualitatively supported by infrared spectroscopy, which indicated that although a small amount of Ti is necessary for disassociating H(2), excess surface Ti (>0.1 ML) hinders the formation of Al-H species.

Enhanced hydrogen storage properties of LiAlH4 catalyzed by CoFe2O4 nanoparticles

“…Among numerous possible hydrogen storage materials, lithium aluminum hydride [7][8][9][10] (LiAlH 4 ) is a promising candidate due to its relatively large theoretical hydrogen storage capacity and high potential reversible hydrogenation capability.…”

“…The X-ray intensity was tested over the 2q angle ranged from 10 to 90 with a scanning velocity of 0.02 per second. (Fig.…”

Synthesis of LiAlH4 Nanoparticles Leading to a Single Hydrogen Release Step upon Ti Coating

“…Hydrogen holds enormous potential to be the ultimate energy carrier of the future [1][2][3][4][5]. Yet the lack of an effective method for storing hydrogen with high density currently restrains its widespread utilization.…”

“…Hence, the reversibility of this step is generally believed to be thermodynamically impossible under practical conditions of temperature and pressure [3,4]. Indeed, theoretical studies have suggested the need for extreme hydrogen pressures >100 MPa at room temperature for the direct regeneration of LiAlH 4 from Li 3 AlH 6 [2,3,5]. In Step 2, Li 3 AlH 6 decomposes via an endothermic reaction with a ∆H of 25 kJ·mol −1 H 2 [6].…”

“…Yet the lack of an effective method for storing hydrogen with high density currently restrains its widespread utilization. Solid state hydride materials offer promising possibilities to deliver high capacity, safe, and compact hydrogen storage systems [5,6]. However, so far no material satisfies all the requirements for practical mobile application [3].…”