Reaction Mechanisms and Dynamics of H2 Generation in Microhydrated Al Clusters: The Role of Oxo–Hydroxyl and Dioxo Structures in the Al17–·(H2O)2 System

The dynamics of the Al17–·(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–·(H2O) and H2Al17(OH)2– 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– can easily undergo further O–H bond breaking to generate the double- and triple-bridged oxo structures H3Al17O(OH)− or H4Al17O2–. On the basis of the dynamics computations, new mechanisms for H2 generation are proposed in which the dioxo structures play an import...