In situ solid state 11B MAS-NMR studies of the thermal decomposition of ammonia borane: mechanistic studies of the hydrogen release pathways from a solid state hydrogen storage material.
In situ solid state 11B MAS-NMR studies of the thermal decomposition of ammonia borane: mechanistic studies of the hydrogen release pathways from a solid state hydrogen storage material.
复制标题
DOI：
10.1039/b617781f
复制
发表时间：
2007-04
期刊：
影响因子：
--
通讯作者：
A. Stowe;W. Shaw;J. Linehan;Benjamin A. Schmid;T. Autrey
中科院分区：
文献类型：
--
作者：
A. Stowe;W. Shaw;J. Linehan;Benjamin A. Schmid;T. Autrey
采用原位固体（11）B和（11）B{（1）H} MAS-NMR技术，在7.1 T和18.8 T外场下，在88 ℃（远低于文献报道的熔点）下，研究了固态氨硼烷（AB）的氢释放机理. AB的分解是通过诱导、成核和生长机理来描述的。在诱导期内，几乎没有氢从AB中释放出来;然而，在（11）B NMR谱中观察到一种被鉴定为AB的移动的相的新物质。在诱导之后，在最初释放氢气的反应时间，观察到三种额外的物质：乙硼烷的二氨化物（DADB），[（NH（3））（2）BH（2）]（+）[BH（4）]（-），以及两种BH（2）N（2）物质，据信是氨基硼烷的线性（NH（3）BH（2）NH（2）BH（3））和环状二聚体（NH（2）BH（2））（2）。在较长的反应时间下，尖锐的特征被包含BH（2）N（2）和BHN（3）物质的复合聚合氨基硼烷（PAB）的宽的、无结构的峰所取代。提出了导致氢形成的AB分解的诱导、成核和生长的以下机理模型：（i）诱导期，其产生由二氢键破坏引起的AB的移动的相;（ii）成核，其从移动的AB产生反应性DADB;和（iii）生长，其包括DADB和AB之间的双分子反应以释放储存的氢。
The mechanism of hydrogen release from solid state ammonia borane (AB) has been investigated via in situ solid state (11)B and (11)B{(1)H} MAS-NMR techniques in external fields of 7.1 T and 18.8 T at a decomposition temperature of 88 degrees C, well below the reported melting point. The decomposition of AB is well described by an induction, nucleation and growth mechanistic pathway. During the induction period, little hydrogen is released from AB; however, a new species identified as a mobile phase of AB is observed in the (11)B NMR spectra. Subsequent to induction, at reaction times when hydrogen is initially being released, three additional species are observed: the diammoniate of diborane (DADB), [(NH(3))(2)BH(2)](+)[BH(4)](-), and two BH(2)N(2) species believed to be the linear (NH(3)BH(2)NH(2)BH(3)) and cyclic dimer (NH(2)BH(2))(2) of aminoborane. At longer reaction times the sharper features are replaced by broad, structureless peaks of a complex polymeric aminoborane (PAB) containing both BH(2)N(2) and BHN(3) species. The following mechanistic model for the induction, nucleation and growth for AB decomposition leading to formation of hydrogen is proposed: (i) an induction period that yields a mobile phase of AB caused by disruption of the dihydrogen bonds; (ii) nucleation that yields reactive DADB from the mobile AB; and (iii) growth that includes a bimolecular reaction between DADB and AB to release the stored hydrogen.