Using Ex Situ and In Situ HERFD-XANES to Reveal the Superior Oxidation and Reduction Cycling of Ceria Nanocubes Dispersed in Silica Aerogel

The oxygen storage capacity of ceria based catalytic materials are influenced by their size, morphology and surface structure, which can be tuned using surfactant-mediated synthesis. In particular, the cuboidal morphology exposes the most reactive surfaces, however, when the capping agent is removed, the nanocubes can agglomerate and limit the available reactive surface. Here, we study ceria nanocubes, lanthanum-doped ceria nanocubes and ceria nanocubes embedded inside a highly porous silica aerogel, by high-energy resolution fluorescence detected - X-ray absorption near edge spectroscopy at the Ce L3 edge. In-situ measurements showed increased reversibility of redox cycles of ceria nanocubes when embedded in the aerogel, demonstrating enhanced reactivity due to the retention of reactive surfaces. These aerogel nanocomposites show greater improvement of the redox capacity and increased thermal stability of this catalytic material compared to the surfactant capped nanocubes. Ex-situ measurements were also performed to study the effect of lanthanum doping on the cerium oxidation state in the nanocubes, indicating a higher proportion of Ce4+ compared to the undoped ceria nanocubes.