Nanocrystalline ceria/zirconia

FIGURE 10.3 Powder x-ray patterns of ceria-zirconia made by using two different liquid carriers for the precursors. The isooctane-hased carrier composition forms a product containing a ceria-rich (Figure 10.2, left peak, hottom trace) and a zirconia-like phase (right peak). In contrast, apphcation of the lanric/acetic acid-based carrier solution resnlts in a single mixed oxide phase (top trace) (From Stark, W.J., Madler, L., Maciejewski, M., Pratsinis, S.E., and Barker, A., Flame synthesis of nanocrystalline ceria-zirconia effect of carrier liquid, Chem. Commun., 5, 588, 2003.)... 

Stark, W.J., Madler, L., Maciejewski, M., Pratsinis, S.E., and Baiker, A., Elame synthesis of nanocrystalline ceria-zirconia effect of carrier liquid, Chem. Com-mun., 5, 588, 2003. 

From W. J. Stark, L. Madler, M. Maciejewski, S. E. Pratsinis, and A. Baiker, Flame-Synthesis of Nanocrystalline Ceria/ Zirconia Effect of Carrier Liquid, Chem. Comm., 588-589 (2003). Reproduced by permission of The Royal Society of Chemistry.]... 

The defective structure in nanocrystalline ceria based catalysts proved to have strong effect on the OSC. Mamontov et al. (2000) reported the neutron diffraction studies of the atomic structures of nanocrystalline powder of ceria and ceria-zirconia solid solution. They found that the concentration of vacancy-interstitial oxygen defects has a direct correlation with the OSC. This effect is stronger than the correlation of surface area with OSC. Zirconia reduces ceria and preserves oxygen defects to retard the degradation of ceria-zirconia in OSC. Yan et al. observed the strong correlation between OSC and the lattice strain in nanosized ceria-zirconia, which could be measured via XRD (Si et al., 2004 Figure 11). 

Kosacki, I., Suzuki, T., Petrovsky, V., and Anderson, H.U., Electrical conductivity of nanocrystalline ceria and zirconia thin films. Solid State Ionics, 2000, 136, 1225-1233. 

Although the emphasis here will, by necessity, be placed on more recent data, several key reviews of transport in nanocrystalline ionic materials have been presented, the details of which will be outlined first. An international workshop on interfacially controlled functional materials was conducted in 2000, the proceedings of which were published in the journal Solid State Ionics (Volume 131), focusing on the topic of atomic transport. In this issue, Maier [29] considered point defect thermodynamics and particle size, and Tuller [239] critically reviewed the available transport data for three oxides, namely cubic zirconia, ceria, and titania. Subsequently, in 2003, Heitjans and Indris [210] reviewed the diffusion and ionic conductivity data in nanoionics, and included some useful tabulations of data. A review of nanocrystalline ceria and zirconia electrolytes was recently published [240], as have extensive reviews of the mechanical behavior (hardness and plasticity) of both metals and ceramics [13, 234]. 

Kazakov AI, Rubtsov Yul, Lempert DB, Manelis GB (2003) Kinetics of oxidation of organic acids by ammonium nitrate. Russ J Appl Chem 76 1214-1220 Behera SK, Barpanda R Prathar SK, Bhattacharyya S (2004) Synthesis of magnesium-aluminium spinel from autoignition of citrate-nitrate gel. Mater Lett 58 1451-1455 Chandradass J, Kim K, Ki H (2004) Effect of activity on the citrate-nitrate combustion synthesis of alumina-zirconia composite powder. Metals Mater Int 15 2039-2043 Purohit RD, Saha S, Tyagi AK (2006) Nanocrystalline ceria powders through citrate-nitrate combustion. J Nanosci Nanotech 6 209-214... 

Active heterogeneous catalysts have been obtained. Examples include titania-, vanadia-, silica-, and ceria-based catalysts. A survey of catalytic materials prepared in flames can be found in [20]. Recent advances include nanocrystalline Ti02 [24], one-step synthesis of noble metal Ti02 [25], Ru-doped cobalt-zirconia [26], vanadia-titania [27], Rh-Al203 for chemoselective hydrogenations [28], and alumina-supported noble metal particles via high-throughput experimentation [29]. 

The present work was focused on the synthesis of nanocrystalline components for electrochemical cells via the cellulose-precursor technique. This method was used to prepare nanostructured intermediate-temperature (IT) SOFC anodes made of a series of cermets comprising gadolinia-doped ceria (CGO), yttria-stabilized zirconia (YSZ), Gdi.86Cao.i4Ti207.5 (GCTO) pyrochlore, metallic nickel and copper. Perovskite-type SrFcojAlo.sOs.s (SFA) powder, also obtained via the cellulose precursor, was applied onto membranes of the same composition to enhance specific surface area and electrocatalytic activity in the reactors for methane conversion [3]. 

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