Figure 2 FESEM images of the CeO 2 SCS nanopowders
at × 40,000 (a) × 10,000 (b) level of magnifications. Finally, Figure 3 illustrates some details of a variety of self-assembled stars. The images show three micrometric star assemblies with different sizes and shapes, thus proving that the residence time in the reactor affects their final size (Figure 3a, 12 h; b, 24 h). This design offers a controlled and repeatable morphology, with a tridimensional shape constituted by individual Quizartinib purchase rods (the fundamental elements that self-assemble into a star), which offer a concave space for soot intrusion. Soot-catalyst contact in loose conditions, before the TPC experiments, was observed by means of FESEM, and is depicted in Figure 4: it is possible to see that an effective soot penetration occurs, more so than would happen with a flat or convex morphology. This behaviour is desirable in the perspective of depositing such SA stars on the surface of the DPF channels as a carrier for noble metals or other active species: BAY 73-4506 hence, an effective penetration of the soot cake through a relevant portion of the catalytic layer would increase the number of contact points between
the soot particles and the catalyst itself, thus promoting catalyst activity. This would overcome the limitation of the catalytic layer obtained with in situ SCS , on the top of which the soot cake grows during soot filtration in the DPF: this generates a soot oxidation mechanism that only involves the interface between the catalyst layer and the soot cake. Figure 3 FESEM images of the CeO 2 SA-stars at 12 h (a) and 24 h (b) different residence times. 4��8C Figure 4 FESEM images representing a loose contact mixture of CeO 2 SA-stars and soot at × 40,000 (a) × 150,000 (b) level of magnifications. CeO2 has a fluorite cubic cell structure. It
has been proved that hydrothermal treatments can expose unstable planes and turn the cube into an octahedron , whose tendency can be inferred from Figure 5. HRTEM investigations are needed to understand whether the obtained SA stars preferentially expose the most active ceria plains to soot oxidation, namely 310, 100 and 110 even completely different structures [12, 18]. These surfaces may be stabilized by defects (such as oxygen vacancy) or by adsorbed charge compensating species, and oxygen vacancies entail more oxygen mobility and availability for soot oxidation . Figure 5 FESEM images of CeO 2 rods at × 38,000 (a) × 14,000 (b) level of magnifications. The X-ray diffraction (XRD) analysis confirmed that all the catalysts belonged to the particular fluorite structure of CeO2 (Fm-3 m). From the comparison of the XRD spectra of the SCS ceria, fibers and SA stars, it is possible to appreciate a wider peak broadening in the star curves (Figure 6): according to the Debye-Scherrer theory, this entails finer crystallites for the SA stars.