Water interaction with oxides

Finding detailed correlation between the energetics of adsorbate-surface interaction and the structural properties of a catalyst is an important fundamental issue and an essential prerequisite for understanding the realistic catalytic processes. Interaction of water with oxide surfaces is particularly important for many technological and environmental applications. In this study, we investigate interaction of water with model Fe3O4(111)/Pt(111) and Fe3O4(100)/Pt(100) surfaces by employing a newly developed single crystal adsorption calorimetry (SCAC) set up to determine the adsorption and dissociation heats of water on these oxides with high accuracy. Complementary, the evolution of water species and their chemical transformations on iron oxide surfaces are monitored by vibrational spectroscopy (IRAS). We show that water dissociates readily on iron oxide surfaces forming a variety of hydroxyl groups and hydroxyl-water complexes. The energetics of these processes depends strongly on the particular surface termination as well as on the surface coverage of species formed during water adsorption and dissociation. Particularly for low water coverages, we show that water dissociates readily on iron oxide surfaces forming a dimer-like hydroxyl-water complex and proved that the generally accepted model of water dissociation to two individual OH groups is incorrect. The combination of adsorption energy measurements with spectroscopic identification of surface species allows us to obtain deep atomistic insights into water interaction with oxides and provide important benchmarks for theoretical calculations. (Dementyev et. al., Angew. Chem. Int. Edit. 54 (2015) 13942-6)

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