X-ray photoelectron spectroscopy study of Pt-cluster-induced electronic-state change of CeO2(111) surfaces

Abstract

We investigated the reduction of a CeO2(111) surface after the deposition of size-selected Pt8 clusters on it via x-ray photoelectron spectroscopy (XPS). Electron transfer from Pt to CeO2(111) results in the reduction of Ce4+ to Ce3+ and the subsequent formation of Ptδ+ atoms at the interface. We quantitatively estimated the reduction from the Ce3+/(Ce3+ + Ce4+) ratio determined from the Ce3d spectra. Approximately 30% of Ce4+ under or in the perimeter of the Pt8 cluster was reduced to Ce3+. The XPS spectra showed an increase in the ratio of Ce3+/(Ce3+ + Ce4+) with an increase in the amount of Pt8 clusters deposited on the CeO2(111) surface. The reduction of 3.7 Ce4+ to Ce3+ per Pt8 clusters, followed by the formation of 3.7 Ptδ+ atoms per Pt8 clusters was observed at 0.006 ML (mono layer) Pt coverage. The actual Ce3+ formation influenced by Pt deposition was approximately 2.5%. We estimate that approximately 30% of Ce4+ under or in the perimeter of a Pt8 cluster was reduced to Ce3+. At a higher coverage of 0.015 ML, the reduction of 2.2 Ce4+ to Ce3+ per Pt8 cluster, followed by the formation of 3.2 Ptδ+ atoms per Pt8 cluster was observed. This implies the aggregation of Pt clusters occurred at a higher Pt coverage. Atomically precise quantification of the electron transfer across the Pt–CeO2(111) interface can enable an improved understanding of the metal-support interaction.