Zirconia solid solutions

M. Mamak, N. Coombs, and G. Ozin, Mesoporous yttria-zirconia and metal-yttria-zirconia solid solutions for fuel cells, Adv. Mater. 12, 198—202 (2000). 

Raw materials are only mixed in a mechanical way so that the mixture of magnesium oxide and zirconia occurs only at the particle level. This increases the difficulty for the diffusion of magnesium oxide into the crystalline zirconia to stabilize it by forming a magnesium oxide-zirconia solid solution. 

Ceria affords a number of important applications, such as catalysts in redox reactions (Kaspar et al., 1999, 2000 Trovarelli, 2002), electrode and electrolyte materials in fuel cells, optical films, polishing materials, and gas sensors. In order to improve the performance and/or stability of ceria materials, the doped materials, solid solutions and composites based on ceria are fabricated. For example, the ceria-zirconia solid solution is used in the three way catalyst, rare earth (such as Sm, Gd, or Y) doped ceria is used in solid state fuel cells, and ceria-noble metal or ceria-metal oxide composite catalysts are used for water-gas-shift (WGS) reaction and selective CO oxidation. 

Related systems It should be noted that specific properties for applications could be enhanced by using solid solutions, doped materials, and composites, instead of pure ceria. For example, ceria-zirconia solid solution is a well known ceria based material for enhanced OSC and high ionic conductivity for solid state fuel cell components. It is also used in the three way catalysts for automobile waste gas cleaning, because of the improved thermal stability, surface area, and reducibility. The synthesis, structure, and properties of ceria-zirconia have been actively studied for a long time. Di Monte and Kaspar et al. presented feature articles on the nanostructured ceria—zirconia-mixed oxides. The studies on phase, structures, as well as the microstructures are discussed and reviewed (Di Monte et al., 2004). 

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). 

The acid-base properties of ceria-zirconia solid solutions [82] and ceria-lanthana co-precipitated mixed oxides have been investigated by Cutrufello and... 

Table 3,4. Mean particle size, BET surface area of ceria and ccha-zirconia solid solutions...

The cubic pyrochlore-based ceria-zirconia solid solution is a good material. However, it has been reported that the reduction temperature has become higher after the high-temperature oxidation.This is due to the transformation from pyrochlore-based-cubic to r -tetragonal phase which is more stable than it, and r ... 

Recently one of the solutions to overcome this problem has been proposed.This does concern surface modification of the pyrochlore-based oxide.s. It is known that cerium and zirconium chlorides provide vapor phase complexes with aluminum chloride at elevated temperatures.The new surface modification technique utilizes the formation of these vapor complexes to remove and modify the top surface of the pyrochlore ceria-zirconia solid solution. This method is named "chemical filing". Application of the above complexes formation has already been demonstrated for the vapor phase extraction and mutual separation of rare earths based on the so-called chemical vapor transport (CVT). ... 

A recent study of Bozo et al concerning platinum deposited onto ceria-zirconia solid solution has been published [45]. Pt/CeOo 7ZrOo33 was a most attractive catalysts which showed an activity much higher than for platinum deposited onto alumina T50 for methane combustion was lowered from 470 to 300 C according to their experimental conditions. This activity was attributed to enhanced oxygen species mobility onto ceria containing solids. Unfortunately a continuous... 

OPCM route of ceria—zirconia solid solutions synthesis appears to be reasonably flexible approach allowing to make rather broad substitution in cation and anion sublattices of fluorite-like oxides without appearance of new phases provided homogeneous mixing of starting salts is ensured. Reasonably high dispersion of samples thus obtained and disordered bulk and surface structure makes them promising candidates as catalysts and supports for red-ox reactions. 

Figure 6. Initial selectivity to 4-methylpent-1-ene as a function of the ns/nA ratio. Full symbols refer to the sanqjles investigated in the present work. Open symbols represent previously investigated catalysts pure and doped zirconias (squares) [4] pure and doped cerias and lanthanas (circles) [5] ceria-zirconia solid solutions (triangles) [6] zirconias prqiared via sol-gel (reversed triangles) [7] ceria-lanthana solid solutions (diamonds) [8].

Role of Zr02 Additive the Ceria-Zirconia Solid Solution... 

Mamak. M. Coombs. N. Ozin, C. Self-assembling solid oxide fuel cell materials Mesoporous yttria-zirconia and metal-yttria-zirconia solid solutions. J. Am. Chem. Soc. 2000. 122 (37). 8932-8939. 

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