An ab initio study on formation and desorption reactions of H2O molecules from surface hydroxyl groups in silicates

Effects of the Al atom on the formation and desorption reactions of H2O molecules from surface hydroxyl groups in silicates have been investigated by ab initio molecular calculations for Si(OH)4 and (HO)3Si(OH)Al(OH)3 cluster models. The analysis of the potential energy profiles for the reactions of surface hydroxyls shows that the H2O complex formation and the H2O desorption through the interaction of the surface hydroxyls with Al(OH)3 units yield relatively low activation energies. The low energies of these reactions are closely connected with the changes of geometrical parameters and charge distributions caused by the interaction of the surface hydroxyls with Al(OH)3 units.