(581d) Universal Properties of Metal-Supported Oxide Films from Scaling Relationships: Elucidation of Strong Metal Support Interactions.

The properties of ultrathin (hydroxy)oxide films on transition metal substrates, which serve as important model systems for well-known catalytic phenomena such as the strong metal support interaction (SMSI), have been extensively studied in both surface science and high pressure environments. However, since these analyses have been primarily carried out on specific model systems, few broad principles exist to predict the formation and properties of the film structures. Here, using Density Functional Theory (DFT) calculations, we provide insights into the general principles that govern film/substrate interactions. We analyze ZnO_xH_y films on a range of transition metal surfaces and find that the formation energies of these films can be reasonably described using the combination of binding energies of Zn and O atoms. Such scaling relationships (SR’s) have been previously identified and have been rationalized using bond order conservation (BOC) principles. However, we found that for ZnO_xH_y films, the standard BOC relationships fail to accurately describe the slopes of these SR’s. We explain this discrepancy with a generalized bonding model based on the assumption that film-surface binding will vary due to changes in the bonding environment. These variations, in turn, are traced to composition-induced changes in the oxidation states of the films’ metal cations. We confirm that the new model can explain and predict the binding energies for ZnO_xH_y films, as well as other common ultrathin film systems such as TiO_xand PtO_x. Finally, we demonstrate that combining the SR’s, along with ab-initio thermodynamic techniques, can provide detailed phase diagrams which help to determine the molecular structure of these films at industrially relevant reaction conditions. The phase diagrams may provide guidance in developing new catalytic active sites through rational exploitation of SMSI-related phenomena.