Oxygen rare earth oxides

Storage are the fresh and 75 h aged Pd ly TWCs (Cl and C2), and it is likely that rare earth oxides do contribute to oxygen up es in those catalysts. Interestingly, the C1 and C2 catalysts are the only pair which show a correlation between oxygen uptake and noble metal dispersion (i-e. the oxygen titrated by the first CO pulse drops from 35.5 to 27.2 /i-mol O/g-cat. as the dispersion drops from 10.8% (Cl) to 3.5% (C2)). 

Dynamometer-aged (120 h) catalysts showed no evidence for oxygen storage via rare earth oxides. 

The reactivity towards oxygen (air, etc.) is, of course, very important. It is well-known indeed, that rare earth metals may readily react with air. The high stability of rare earth oxides, as shown in Fig. 6.9, makes it evident that rare earth metals are unstable in the presence of oxygen. As one may expect, the rate of oxidization will depend on several variables it will be higher when the level of the most common impurities, the relative humidity, the temperature are higher and when the atomic number of the lanthanide is lower. 

Dr. Clifford Yes, the quadrupole splitting for iron in rare earth oxides was perhaps 1% times the value reported in any of the iron oxides themselves. This is probably caused by the fact that in the iron oxides the asymmetry in the crystal is in the second coordination sphere. In other words, it is caused by the presence or absence of the nearest iron atoms in the lattice, whereas in the rare earth oxides, it s an oxygen deficiency in the first coordination sphere of the iron, assuming that the iron took a normal lattice position in the rare earth oxide. 

Many of these vapours will break down spontaneously to atoms in the flame. Others, particularly diatomic species such as metal monoxides (e g. alkaline earth and rare earth oxides), are more refractory. Monohydroxides which can form in the flame can also give problems. The high temperature and enthalpy of the flame aid dissociation thermodynamically, as does a reducing environment. The role of flame chemistry is also important. Atoms, both ground state and excited, may be produced by radical reactions in the primary reaction zone. If we take the simplest flame (a hydrogen-oxygen flame), some possible reactions are the following ... 

The loss of oxygen alone from transition metal oxides has been widely reported (Table II). Those with the fluorite structure can lose oxygen as well as gain it, and the over-all similarity to the C-type rare-earth oxide structure led to the... 

Stable phases in the rare earth oxide systems are tabulated and discussed. New data on the structure of sesquioxides quenched from the melt are reported. The structural interrelations between the A, B, and C type sesquioxides and the fiuorite dioxides are pointed out. The sequences of several intermediate oxides in the CeO, PrO., and TbO, systems are observed to be related to the fluorite structure and the C form sesquioxide with respect to the metal atom positions. A hypothetical homologous series of the general formula Mn02n i, related to the fluorite structure and the A form sesquioxide with a more or less fixed oxygen lattice, is suggested. 

Lower Oxides. The question of the incorporation of oxygen into the rare earth metal lattice and the extent of oxide formation between the metal and the sesquioxide has not been systematically studied. The lower oxides reported in Table I were prepared by distilling the rare earth metals in a system of low oxygen partial pressure (9). This is one of the great unexplored regions of the rare earth oxide systems. 

Coordination in M203 and M02 Phases. In the several rare earth oxides the configuration of oxygen atoms around the metal atom is found to be one of several different types. 

The electrical conductivity of rare-earth oxide fluorides was first investigated for the development of a binary anion conductive solid electrolyte. As a result, it was found that the binary rare-earth oxide fluorides exhibited oxide ion conductivity. Among them, the conductivity of neodymium europium oxide fluoride, Nd2Eu203F6, was reported to be much higher than that of yttria-stabilized zirconia, YSZ, practically used as an oxygen sensor [34]. The electrical conductivities of the binary rare-earth oxide fluorides vary not only with the combination of Ln203 with Ln F3... 

Fig. 7. The electrical conductivities of binary rare-earth oxide fluorides, Ln-Ln 203F6 measured at 650 C under an oxygen partial pressure of 1.33 x 10 Pa. , more than 1 Sm 1 3 0.1-1 Sm Q, less than 0.1 S m (reproduced with permission from Solid State Ionics, 23 (1989) 99 [19]).

Exclusion of water and oxygen is the primary criterion in rare earth oxysulfide synthesis procedures. This is generally analogous to the case of rare earth sulfides. The industry synthesis technology depends on sulfurizing rare earth oxide powders via solid-state reactions. For instance, the classical sulfide fusion method follows the schematic reaction ... 

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