Kinetic study and determination of the enthalpies of activation of the dehydrogenation of titanium- and zirconium-doped NaAlH4 and Na3AlH6
Kinetic study and determination of the enthalpies of activation of the dehydrogenation of titanium- and zirconium-doped NaAlH4 and Na3AlH6
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DOI：
10.1021/jp034543h
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发表时间：
2003-09
影响因子：
2.9
通讯作者：
T. Kiyobayashi;S. Srinivasan;Dalin Sun;C. Jensen
中科院分区：
文献类型：
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作者：
T. Kiyobayashi;S. Srinivasan;Dalin Sun;C. Jensen
在 363−423 K 的温度范围内测量了掺杂 2 mol% Ti 或 Zr 的铝氢化钠 NaAlH4 和 Na3AlH6 的脱氢速率。直接掺杂钛后，NaAlH4 和 Na3AlH6 以相同的速率进行脱氢。然而，由 Ti 掺杂的 NaAlH4 脱氢产生的 Na3AlH6 的脱氢速率要慢得多。速率常数由脱氢曲线的斜率确定。根据 Eyring 理论，确定 Ti 掺杂的 NaAlH4 和 Na3AlH6 的脱氢反应活化函 ΔH⧧ 为 ∼100 kJ·mol-1，Zr 掺杂的 NaAlH4 和 Na3AlH6 的脱氢反应活化函为 ∼135 kJ·mol-1。这些结果表明，脱氢反应途径对掺杂剂的性质和分布高度敏感，但对 [AlH4]- 和 [AlH6]3- 复合阴离子中 Al−H 键相互作用的差异不敏感。此外，我们得出的结论是，动力学可能受到成核和生长等过程的影响和/或……
The rates of the dehydrogenation of the sodium alanates NaAlH4 and Na3AlH6 doped with 2 mol % Ti or Zr have been measured over the temperature range 363−423 K. NaAlH4 and Na3AlH6 undergo dehydrogenation at equal rates upon direct doping with titanium. However, Na3AlH6 arising from the dehydrogenation of Ti-doped NaAlH4 undergoes dehydrogenation at much slower rates. Rate constants were determined from the slopes of the dehydrogenation profiles. On the basis of Eyring theory, the enthalpies of activation, ΔH⧧, for the dehydrogenation reactions were determined to be ∼100 kJ·mol-1 for both Ti-doped NaAlH4 and Na3AlH6 and ∼135 kJ·mol-1 for both Zr-doped NaAlH4 and Na3AlH6. These results suggest that the dehydrogenation reaction pathways are highly sensitive to the nature and distribution of the dopant but not to differences in the Al−H bonding interactions in [AlH4]- and [AlH6]3- complex anions. Furthermore, we conclude that the kinetics are probably influenced by processes such as nucleation and growth and/o...