Adsorption and dissociation of water on relaxed alumina clusters: a first principles study

Using previous results for the equilibrium geometries of stoichiometric (Al 2 O 3 ) n clusters as models for non ideal alumina surfaces, we obtain, from ab‐initio total energy LCAO calculations, the corresponding relaxed structures of the complexes H 2 O–(Al 2 O 3 ) n with n ≤ 7. Depending on the initial position of the water molecule relative to the cluster site, the complex evolves to different equilibrium structures, with and without dissociation of H 2 O, whose energetic, bond lengths, and charge transfer trends are studied as the morphology and size of the initial cluster change. Dissociation of H 2 O with the radical OH – bound on top of an Al atom and the proton H + bound to the second nearest neighbour O, is the dominant process for the reaction (Al 2 O 3 ) n + H 2 O with n = 4, in agreement with the one observed for the adsorption of H 2 O on the extended real surface. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)