Interaction of silver nano-clusters with ceria thin-films: An in situ temperature dependent x-ray photoelectron spectroscopy study

Abstract

Temperature dependent oxidation states of ceria (CeO 2 ) are observed at much lower temperatures in presence of silver nano-clusters (NCs), deposited on CeO 2 thin-films, using a nano-cluster deposition system equipped with quadrupole mass filter assembly and x-ray photoelectron spectroscopy (XPS) facilities. In situ high-temperature XPS studies indicate that CeO 2 oxidizes Ag-NCs to AgO at room temperature and reduces to Ce 3+ state at much lower temperature. Further, a temperature dependent reversible change in oxidation states between Ag(III) and Ag(II) states is observed. Transmission electron microscopy (TEM) study reveals that besides coalescence of silver clusters during heating, the Ag-NCs interact with CeO 2 resulting in fully covered Ag-NCs by a layer of CeO 2 due to strong metal support interactions (SMSI). UV-Vis studies show a decrease in bandgap of CeO 2 due to an increase in Ce 3+ content in CeO 2 film responsible for SMSI effect at the interface of silver clusters and cerium oxide at higher temperature. Interactions at the adsorption edge between CeO 2 and Ag-NCs help to decrease the bandgap of CeO 2 in presence of Ag-NCs. Thus the presence of silver clusters plays a crucial role in lowering the oxidation-reduction temperature of ceria. Overall, the Ag-NC in ceria helps to reduce Ce 4+ state to Ce 3+ state at much lower temperature that would be useful for its different low-temperature catalytic applications. • Ag-NCs grown on CeO 2 are in oxidized state at room temperature as evident from XPS study. • After a heating cycle, Ce 3+ enriched CeO 2 film is found at room temperature where only Ce 4+ state is present before heating. • A reversible change in oxidation state of Ag is observed where temperature is varied from RT to 250 °C. • The room temperature TEM study indicates a strong metal support interaction at the interface of ceria and silver clusters.