Formation and Three-dimensional Microstructure of Ceria-Related Nanomaterials

Notwithstanding the promising catalytic properties of novel porous ceria nanomaterials, their nanostructure has remained incompletely explored. Ceria and its related materials have remained at the centre of extensive catalytic applications. More recently, the capabilities of these materials have been combined with novel porous morphologies to overcome new challenges in environmental and industrial catalysis. This study aims to determine the nanoscale mechanisms that drive the formation of porous ceria nanomaterials. Such an understanding is instrumental in advancing the design and applications of these novel materials. By implementing different techniques across electron microscopy, this work complements the findings of catalysis groups who have evidenced the higher catalytic performance of porous vs non-porous ceria nanomaterials.
Based on a review of the literature, two fabrication methods of porous ceria were selected. In one case, pores were induced by annealing ceria nanomaterials at 800 and 950 *C. In the other, porous ceria was synthesised from a precursor via a nanocasting method. The intermediate and final products of these two approaches were characterised in detail using electron microscopy for imaging, analysis and tomographic reconstructions. For pre-synthesised nanoparticles, the studies here were able to resolve, for the first time, the full 3D shape and location of the pores, as well as their crystallographic alignment. Furthermore, the present work has shown transformations at previously unpublished near-sintering temperatures. This experiment rendered the first reported occurrence of porous defects in annealed nanocubes. The present work shows a novel image-processing algorithm, which expands the capabilities of reduced- information tomography techniques to reconstruct porous materials. Further research could use this new method to reconstruct currently unresolved porous and multi-phase structures. As for nanocasting products, the advanced characterisations determined the correlation between characteristics of the template and the product. To establish this relation here is reported the first infiltration of MSU-F to form a silica/ceria composite.