DFT study of the thermodynamic stability of Pd-Pt bulk oxide phases

The catalytic combustion activity of PdPt bimetallic catalysts is governed by oxide phases which form under oxygen-rich operation conditions. We investigate the thermodynamic stability of mixed PdxPt1-xOy phases with the crystal structures of PdO, PtO2, and Pt3O4 within an ab initio thermodynamics framework based on density-functional theory calculations. Our results suggest a complex mixing-demixing behavior of the Pd-Pt-O system upon variations of temperature and oxygen partial pressure. At atmospheric pressure mixed oxides are predicted to be stable only at temperatures below 400-500 K, whereby the presence of Pd 41 ions is stabilized with increasing Pt amount in a PdxPt1-xO2 phase. At intermediate temperatures a mixture of phases becomes stable where PdO coexists with PtO2 or Pt3O4. At high temperatures the oxides decompose directly to form PdPt alloys, except for Pd-rich systems, where PdO and metallic Pt coexist within a small temperature window.