Department of Energy Science and Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India.
Dalton Trans. 2018 May 8;47(18):6570-6579. doi: 10.1039/c8dt00789f.
The thermolytic decomposition of ammonia borane (AB) is known to proceed through the polymeric coupling reaction between -BH3 and -NH3 sites of multiple ammonia borane molecules, which results in the release of hydrogen and other by-products, e.g., ammonia, diborane and borazine. The formation of these by-products concomitantly pollutes the hydrogen stream, and therefore, it is necessary to remove these gases from the product stream. In the current work, a cost effective and easy to synthesize support material, aluminium phosphate (AP), is introduced in AB thermolytic decomposition. An in situ MS study reveals that the AB and AP (w/w) loading ratio of (1 × 4) is the most promising as it is able to minimise the dehydrogenation peak temperature by 18.89 °C compared to that of pure AB. Additionally, in the presence of support material, the by-product formation of ammonia is reduced by 70.3%, with a complete suppression in borazine and diborane release. The mechanism behind the by-product suppression of supported AB has been studied through 11B MAS NMR analysis which suggests that the release of hydrogen occurs through an intermolecular homopolar B-B bonding. The thermogravimetric and kinetic study also reveals that in the case of supported AB decomposition, hydrogen release through B-B interaction is much more efficient than a B-N interaction, thus limiting the possibility of autocatalysis during the supported decomposition reaction.
氨硼烷（AB）的热分解已知是通过多个氨硼烷分子的-BH3 和 -NH3 位点之间的聚合偶联反应进行的，这导致氢气和其他副产物的释放，例如氨、硼烷和硼嗪。这些副产物的形成同时污染了氢气流，因此需要从产物流中去除这些气体。在当前的工作中，引入了一种成本效益高且易于合成的支持材料磷酸铝（AP），用于 AB 的热分解。原位 MS 研究表明，AB 和 AP（w/w）负载比为（1×4）是最有前途的，因为它能够将脱氢峰温度比纯 AB 降低 18.89°C。此外，在支持材料存在的情况下，氨气的副产物形成减少了 70.3%，硼嗪和硼烷的释放完全抑制。通过 11B MAS NMR 分析研究了负载 AB 抑制副产物的机理，这表明氢气的释放是通过分子间同极 B-B 键合发生的。热重和动力学研究还表明，在负载 AB 分解的情况下，通过 B-B 相互作用释放氢气比 B-N 相互作用更有效，从而限制了负载分解反应过程中自催化的可能性。
