Plane wave density functional model studies of chemistry at surfaces

Quantum chemical studies on the hydrogenation of acrolein by means of a silver catalyst and the sorption of uranyl on kaolinite are presented as examples of computational modeling of surface species and chemical processes at the atomic scale. A plane-wave density functional approach as implemented in the parallel program package VASP was applied on supercell models of these surface systems to determine electronic and geometric structures as well as energetic properties. While hydrogen does not interact with silver surfaces, oxygen impurities are shown to activate molecular hydrogen, hence are suggested as centers where atomic hydrogen may be produced over silver catalysts. The reactivity and selectivity of silver surfaces for acrolein hydrogenation to propenol is demonstrated in agreement with experimental findings by modeling the reaction mechanism and its kinetics in detail. For uranyl adsorption on different ideal surfaces of the mineral kaolinite, it is shown that, as expected, complexation depends on the protonation of the surface. Alumina terminated faces of kaolinite are more reactive than silica terminated surfaces. In contrast to experimental assignments, also some outer sphere model complexes are shown to reflect in their geometry interaction with the mineral surface.