Synthesis and hydrogen release properties of alkyl-substituted amine-boranes
Three organic amine-boranes-diethylenetriamine-borane (C4H13N3·3BH3, DETAB), triethylenetetramine-borane (C6H18N4·4BH3, TETAB) and tetraethylenepentamine-borane (C8H23N5·5BH3, TEPAB)-are synthesized via the liquid-phase reaction of diethylenetriamine (C4H13N3, DETA), triethylenetetramine (C6H18N4, TETA) and tetraethylenepentamine (C8H23N5, TEPA), respectively, with BH3-THF solution. By using high-resolution synchrotron powder X-ray diffraction (HR-XRD), Fourier transform infrared (FTIR), elemental analysis and solid-state 11B nuclear magnetic resonance (NMR) measurements, the structural properties of the three compounds are characterized. Hydrogen desorption properties of these compounds are measured by temperature-programmed desorption (TPD) and thermogravimetry (TG) over a temperature range from 50 to 250 °C, in which 5.5, 6.6 and 6.9 equivalents hydrogen are released in two steps based on the combination of protic (N-H) and hydridic (B-H) hydrogens. It is confirmed by mass spectrometry (MS) results that only H2 is liberated during the thermal decomposition of the three compounds. The dynamics are investigated by isothermal dehydrogenation at various temperatures. Compared with ammonia borane (NH3BH3, AB), these compounds show a faster dehydrogenation rate. A regeneration study shows that DETAB can be regenerated by treating its dehydrogenated products with lithium aluminium hydride (LiAlH4) and ammonium chloride (NH4Cl) at room temperature.