Ceria Nanocubes: Dependence of the Electronic Structure on Synthetic and Experimental Conditions

Abstract

The properties of nanostructured ceria are both size- and shape-dependent. Here, ∼3–10 nm ceria nanocubes having exposed (002) surfaces were hydrothermally synthesized. For the first time, the electronic properties of such nanocubes were systematically studied using X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Comparisons of the collected Ce 3d XPS spectra after a single sweep revealed that the concentration of Ce3+ present within the nanocubes is independent of the particle size and the Ce precursor used. Ce 3d spectra collected after averaging 20 sweeps demonstrated the reduction of Ce4+, and that the degree of reduction was also independent of the synthetic conditions. This observed surface reduction/damage is mainly the result of exposure to high intensity X-ray radiation. These conclusions were further confirmed through examination of Ce M4,5- and N4,5-edge XANES spectra. On the basis of these results, it is clear that the concentration of Ce3+ on the surface of ceria nanocubes is independent of the particle size. This fact will become essential when designing new and improved catalytic support systems as the size of the nanocubes will not affect the surface concentration of Ce3+, and therefore may not affect their potential catalytic activity.

Assessing the oxidation states and structural stability of the Ce analogue of brannerite

“…It has been demonstrated previously that both Ce M 4,5 ‐edge XANES spectra and Ce 3d XPS spectra, which both result from the excitation of Ce 3d electrons, are highly sensitive to changes in the Ce oxidation state . This increased sensitivity is a result of the greater resolution of these spectra compared with the resolution of Ce L 3 ‐edge XANES spectra.…”

“…The reasons for the different features present in the spectra have been discussed in detail previously along with the method used to fit these spectra (see Fig. ); however, a short description is provided here . Eight peaks were used to fit the spectrum from CeO 2 , which may also contain traces of Ce 3+ because of surface defects.…”

Ceria Catalysts at Nanoscale: How Do Crystal Shapes Shape Catalysis?

“…This is due to the relatively simple preparation procedure coupled with their shape stability that allows characterization under various conditions. The structure of a CeO2 nanocube is a particle enclosed by six {100} faces with size ranging from a few nanometers 93 to more than 100 nm 76 . The ideal cubic structure is seldom shown in literature and more frequently nanocubes show round corners and edges which expose {111} and {110} surfaces, respectively ( Figure 7) 74 .…”

Oxidation-state sensitive imaging of cerium dioxide by atomic-resolution low-angle annular dark field scanning transmission electron microscopy

“…Specific to CeO 2 , previous studies have demonstrated that the electron beam acts in a reducing manner and drives the transition from Ce 4+ to Ce 3+ as reflected in EELS and high-resolution transmission electron microscopy (HRTEM) exit wave reconstruction measurements [16–18]. It is worth noting that this effect is not limited to electron-based techniques, as any high energy radiation, such as X-rays, can also reduce CeO 2 [19–21]. Therefore, the use of lower accelerating voltages and short probe dwell times to minimize beam damage further emphasizes the importance of efficient experimental design and aberration-correcting optics [7, 22].…”