Computational studies of the interaction of water molecules with different types of solid surfaces will be reviewed, many of which have been performed in close collaboration with experiment. Structural models will be presented for different water loadings ranging from a few water molecules to surfaces covered with several layers of water. Combining quantum mechanical (QM) calculations with single-crystal x-ray diffraction it became possible to follow the evolution of water structures in metal-organic frameworks (MOFs). The applied methods reflect the development from ab initio QM studies on cluster models and force field studies on periodic models to hybrid high level QM – low level QM studies on cluster models embedded in a periodic environment. The latter allows to go beyond the limitations of density functional theory (DFT) for periodic systems and reach chemical accuracy. For the MgO(001) surface, global optimization methods based on a genetic algorithm show that part of the molecules in a water monolayer are dissociated, whereas single molecules remain intact. For two layers of water, constraint MD simulations show that Mg2+ ions may move out of the surface and form solvated ions above the surface. For vanadia supported on zirconia or silica the important role of surface hydroxylation is demonstrated, for example for anchoring the active oxide species on the support. For monomeric O=V(OH)3 species on silica, condensation of OH groups is likely to occur under usual conditions depending on the local surface structure, whereas anchoring by just one V-O-Si bridge proposed based on spectroscopic results is unlikely. The results for water molecules at Brønsted sites in zeolites show that isolated molecules are molecularly adsorbed while for water clusters there is an increased tendency of proton transfer in agreement with their increased basicity. Hydrolysis of Si-O-Si and Si-O-Al bonds is also considered which leads to defective zeolite structures such as vicinal SiOH pairs or partial dealumination.

Award Address (ACS Award in Surface Chemistry sponsored by Procter & Gamble). The interaction of water with solid surfaces: Zeolites, metal oxides, metal-organic frameworks

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