Native Oxidation State Mapping of Ceria via Direct Detection EELS

Abstract

Mapping of ceria oxidation states using electron energy loss spectroscopy has previously been limited to electron flux above the critical threshold for reduction of ceria surfaces (∼3 × 105 e−nm−2s−1). Here, direct electron detection was applied to map the oxidation state of cerium in ceria nanoparticles at low flux (1.25 × 105 e−nm−2s−1). When utilizing direct electron detection, sufficient signal-to-noise was obtained to quantify the native cerium oxidation state in nanometer-resolution maps, which was found to be predominantly Ce4+, but varies significantly based on the sample preparation method. Additionally, local surface reduction of ceria by supported palladium nanoparticles was mapped and quantified. These findings provide insights into the influence of preparation method and palladium incorporation on ceria reducibility and surface chemistry.