Abstract
? 2022 Elsevier B.V.Temperature dependent oxidation states of ceria (CeO2) are observed at much lower temperatures in presence of silver nano-clusters (NCs), deposited on CeO2 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 CeO2 oxidizes Ag-NCs to AgO at room temperature and reduces to Ce3+ 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 CeO2 resulting in fully covered Ag-NCs by a layer of CeO2 due to strong metal support interactions (SMSI). UV-Vis studies show a decrease in bandgap of CeO2 due to an increase in Ce3+ content in CeO2 film responsible for SMSI effect at the interface of silver clusters and cerium oxide at higher temperature. Interactions at the adsorption edge between CeO2 and Ag-NCs help to decrease the bandgap of CeO2 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 Ce4+ state to Ce3+ state at much lower temperature that would be useful for its different low-temperature catalytic applications.
NSTL
Elsevier