Reaction Mechanisms and Dynamics of H2 Generation in Microhydrated Al Clusters: The Role of Oxo鈥揌ydroxyl and Dioxo Structures in the Al17鈥?/sup>路(H2O)2

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• 作者：Sonia 脕lvarez-Barcia ; Ux铆a Rivero-Gonz谩lez ; Jes煤s R. Flores
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：September 24, 2015
• 年：2015
• 卷：119
• 期：38
• 页码：21928-21942
• 全文大小：1178K
• ISSN：1932-7455

文摘

The dynamics of the Al₁₇^{鈥?/sup>路(H₂O)₂ system has been studied by means of potential energy surface computations combined with quasiclassical molecular dynamics simulations and transition state theory computations. The complete process of H₂ generation has been analyzed. The system first undergoes water-splitting steps, generating HAl₁₇OH鈥?/sup>路(H₂O) and H₂Al₁₇(OH)₂鈥?/sup> species. The cluster flexibility plays a major role in the dynamics, because it allows for a quick allocation of the excess energy of the hydrogen atom that splits from water. The result appears to be that H₂ production is significantly delayed by the complexity of the potential energy surface and the presence of long-lived intermediates. It turns out that the dihydroxyl structures H₂Al₁₇(OH)₂鈥?/sup> can easily undergo further O鈥揌 bond breaking to generate the double- and triple-bridged oxo structures H₃Al₁₇O(OH)鈭?/sup> or H₄Al₁₇O₂鈥?/sup>. On the basis of the dynamics computations, new mechanisms for H₂ generation are proposed in which the dioxo structures play an important role. It is also shown that some intermediates have distorted forms of the Al frame that can be traced back to low-lying structures of the Al₁₇鈥?/sup> cluster. Tunneling does not appear to play a critical role, except in the first reaction steps, the water-splitting processes. The impact of the variation of the total energy of the system on the onset of H₂ production and on the mechanism is discussed. Some conclusions could be applicable to the reaction of many other Al clusters with water.}