Reactive insights into the hydrogen production from ammonia borane facilitated by phosphonium based ionic liquid

Abstract

The current work presents a mechanistic insight of hydrogen production from ammonia borane (AB) facilitated by the phosphonium based ionic liquid (IL), trihexyl(tetradecyl)phosphonium bis (2,4,4-trimethylpentyl) phosphinate ([TDTHP][Phosph]). Prior to experiments, the IL was screened from a pool of 11 phosphonium ILs with the infinite dilution activity coefficients (IDAC) values as predicted by conductor like screening model segment activity coefficient (COSMO-SAC) theory. Thereafter, a dehydrogenation experiment of AB/[TDTHP][Phosph] was carried out at 105 °C and 4×10-2 mbar of gauge pressure, which yielded 2.07 equivalent hydrogen production. At higher temperature, the 11B NMR characterization shows the suppression of induction period at 105 °C and appearance of borohydride anion after 1 min of dehydrogenation. Further, time-resolved characterization of AB/[TDTHP][Phosph] at 105 °C confirmed the appearance of polymeric aminoborane after 10min with a subsequent formation of polyborazylene. HR-MS characterization coupled with 1H resonance spectrum confirmed structural integrity of IL. The dual characterization of NMR and HR-MS led us to propose a dehydrogenation mechanism of AB/[TDTHP][Phosph] system.