A comparison between metal supported c-ZrO2 and CeO2

Abstract

We present periodic density-functional theory calculations within the GGA Hamiltonian for monolayers of Pd and Pt supported on the {111} surfaces of cubic-ZrO₂ and CeO₂. We find that the adsorption energies for the Pd-layer on both the zirconia and ceria supports are ca. 200 kJ mol⁻¹, while the corresponding adsorption energies for the Pt-layers are ca. 400 kJ mol⁻¹. Our calculations also predict that the Pt–Pt interactions are three times stronger (∼300 kJ mol⁻¹) than the corresponding Pd–Pd interactions, explaining the different cluster shapes and metal growth modes observed experimentally. Our calculations indicate that the electronic structure of the support determines the geometrical structure of the interface: a tilting of ca. 20° compared to the underlaying ZrO₂ substrate is identified, which is not observed for the CeO₂ substrate. Furthermore, we propose that the bonding character between the metal ad-layers and the oxide supports is dominated by electrostatic forces, owing to the polarisation of the metal ad-layers; yet a weak hybridisation between the outermost oxygen ions and the metal ad-layers is also present. The CeO₂ interfaces investigated show metallic properties as a result of metal induced gap states originating from the metal ad-layers, while the ZrO₂ interfaces show a small band gap of ca. 0.1 eV.