EELS Analysis of Ce Valence State of SiO2 Supported CeO2 Nanoparticles, CeOx Nanoclusters and Ce Single Atoms

Recent advances in catalysis by supported single metal atoms have demonstrated their superior performance for many important catalytic reactions [1].We previously reported the anchoring of metal atoms by dispersing CeOx nanoglues onto high-surface-area SiO2 support to confine the movement of supported metal atoms and to significantly enhance the activity/stability of the Pt1/CeOx/SiO2 for CO oxidation reaction [2].The redox capability of CeO2 surfaces and CeOx clusters play an important role in determining both the activity and stability of ceria supported metal atoms.Spatially resolving the distribution of Ce 3+ and Ce 4+ in supported CeOx particles/clusters is of importance for understanding the catalytic behavior of CeOx supported single metal atoms and clusters.The electron energy loss spectroscopy (EELS) in an aberration-corrected STEM instrument can be utilized to provide such information on an atomic scale.Recent report has demonstrated that the distribution of Ce valence states of CeO2 nanoparticles strongly depends on particle size and facet [3].However, most of the previous work focused on CeO2 nanoparticles with sizes > 3 nm.In this work, we investigate the change of valence state of Ce in the form of CeO2 nanoparticles, CeOx nanoclusters ( 1 nm) and supported Ce single atoms.