Theoretical Insights into the Interaction of Oxygenated Organic Molecules and Cobalt(II) Precursor with γ-Al2O3Surfaces

Abstract

The interaction of two common oxygenates, ethylene glycol (EG) and acetic acid (AA), with the main exposed (100) and (110) surfaces of γ-Al2O3 are investigated by quantifying the thermochemistry of the drying process. Using density functional theory (DFT) calculations, we determine adsorption free energies and identify the adsorption modes and sites for both molecules interacting with the (100) and (110) surfaces of γ-Al2O3 at various coverages. While the affinity of both molecules is stronger for the (100) surface after drying, EG is more strongly adsorbed on alumina surfaces than AA. EG preferentially interacts through hydrogen bonds on the hydroxyl nests of the (100) and (110) surfaces, while it may also interact through Al–O bonds on the (110) surface at low coverage. AA is predominantly deprotonated and interacts as acetate anions through hydrogen bonds on the (110) and (100) surfaces and through Al–O bonds on the (100) surface at low coverage. We then propose a quantitative comparison of the interaction of Co2+ hexaaquo precursor with the same γ-Al2O3 surfaces. The adsorption configurations of the two organic molecules which may hinder the epitaxial growth of cobalt oligomers on alumina surfaces are identified. However, the thermodynamic analysis shows that EG and AA are less stable than the Co precursors after drying. The strong stabilization of Co precursors is attributed to its epitaxial relationship with the dried alumina surfaces as found in [Angew. Chem. Int. Ed. 2015, 54, 6824–6827] and also to a favorable entropy change during the drying process (vapor release and nitrate counterion decomposition in the gas phase). We finally discuss how these effects can be circumvented by changing the conditions of preparation and drying.