Size-Dependent Redispersion or Agglomeration of Ag Clusters on CeO₂

Supported metal nanoparticles tend to agglomerate at high temperatures. Herein, we report that Ag clusters supported on CeO2 prepared by a deposition-precipitation method followed by calcination at 200 degrees C undergo size-dependent redispersion or agglomeration processes upon further calcination at 500 degrees C, accompanied by segregation and reduction of Ag+ cations dissolved in CeO2. Fine Ag clusters with a detectable Ag-O coordination shell using EXAFS redisperse, while large Ag clusters only with a detectable Ag-Ag coordination shell agglomerate. We propose that segregation and reduction of Ag+ cations dissolved in CeO2 upon calcination at 500 degrees C create additional surface oxygen vacancies capable of dismantling fine Ag clusters due to strong Ag-surface oxygen vacancy interaction. The catalytic activity of acquired Ag/CeO2 varies sensitively with the dispersions of supported Ag clusters. These results highlight the important role of surface restructuring of oxide supports in redispersing supported metal clusters.