Two series of nanostructured oxidized copper-cerium catalysts with varying copper loadings, and prepared, respectively, by impregnation of ceria and by coprecipitation of the two components within reverse microemulsions, have been characterized in detail at structural and electronic levels by X-ray diffraction (XRD), Raman spectroscopy, high-resolution electron microscopy (HREM), X-ray energy dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS) (including Ar + -sputtering), and X-ray absorption fine structure (XAFS). These results have been correlated with analysis of their catalytic properties for preferential oxidation of CO in a H 2 -rich stream (CO-PROX), complemented by Operando-DRIFTS. A relevant difference between the two series of catalysts concerns the nature of the support for the surface-dispersed copper oxide entities, which is essentially ceria for the samples prepared by impregnation and a Ce-Cu mixed oxide for those prepared by microemulsion-coprecipitation. The existence of copper segregation in the form of copper oxide or copper-enriched Cu-Ce mixed oxides for the latter type of samples is uniquely revealed by nanoprobe XEDS and XPS Ar + -sputtering experiments. The CO oxidation activity under CO-PROX conditions is correlated to the degree of support-promoted reduction achieved by the dispersed copper oxide particles under reaction conditions. Nevertheless, catalysts which display higher CO oxidation activity are generally more efficient also for the undesired H 2 oxidation reaction. The balance between both reactions results in differences in the CO-PROX activity between the two series of catalysts which are examined on the basis of the structural differences found.

Nanotomography is a technique of growing importance in the investigation of the shape, size, distribution and elemental composition of a wide variety of materials that are of central interest to investigators in the physical and biological sciences. Nanospatial factors often hold the key to a deeper understanding of the properties of matter at the nanoscale level. With recent advances in tomography, it is possible to achieve experimental resolution in the nanometre range, and to determine with elemental specificity the three-dimensional distribution of materials. This critical review deals principally with electron tomography, but it also outlines the power and future potential of transmission X-ray tomography, and alludes to other related techniques.

Colloidal cerium oxide (CeO2) nanocrystals prepared by hydrothermal synthesis were characterized by high-resolution transmission electron microscopy (HRTEM) and three-dimensional electron tomography (3D-ET). HRTEM images of individual CeO2 nanocrystals were then simulated by Blochwave and multislice simulations to determine the atomic arrangement and terminating atoms. The edge length distributions were between 5.0 and 8.0 nm with an average edge length of 6.7 nm. The HRTEM images showed that the CeO2 particles were slightly truncated revealing {220} facets. 3D-ET revealed that the CeO2 nanocrystals exposed predominantly {200} cubic facets. The nanocrystals were truncated at the corners exposing {111} octahedral facets and at the edges {220} dodecahedral facets. Furthermore, 3D-ET revealed the presence of some tetragonal-shaped CeO2 nanocrystals.