Spinel oxidation with

Spinel oxides with a general formula AB2O4 (i.e. the so-called normal spinels) are important materials in industrial catalysis. They are thermally stable and maintain enhanced and sustained activities for a variety of industrially important reactions including decomposition of nitrous oxide [1], oxidation and dehydrogenation of hydrocarbons [2], low temperature methanol synthesis [3], oxidation of carbon monoxide and hydrocarbon [4], and oxidative dehydrogenation of butanes [5]. A major problem in the applications of this class of compound as catalyst, however, lies in their usually low specific surface area [6]. 

Figure 4. Evolution of the a parameter of fee unit cell of spinel oxides with temperature, obtained by different methods. TA means post-treatment with mineral acid.

The detection of transferred hyperfine interaction at diamagnetic Sn cations in oxides of the garnet type (see Chapter 14) prompted a study of isoelectronic Sb + in magnetic oxides of the phase Nii+jxFei 3 Sb,04 [28]. These are spinel oxides with antimony at the octahedral B sites and Fe and Ni distributed on both the tetrahedral A sites and the B sites. The preliminary data show considerable magnetic interactions at the Sb sites, but... 

FIGURE 9.10 Microstructural changes in irradiated spinel oxide with (a) H+ and (b) Li ions to a fluence of 10 5 ions cnr. ... 

Barrett and his colleagues , and Kosakhave summarised existing information on the scales formed on nickel-chromium alloys. Up to about 10% Cr, the thick black scale is composed of a double layer, the outer layer being nickel oxide and the inner porous layer a mixture of nickel oxide with small amounts of the spinel NiO CrjOj. Internal oxidation causes the formation of a subscale consisting of chromium oxide particles embedded in the nickel-rich matrix. At 10-20% Cr the scale is thinner and grey coloured and consists of chromium oxide and spinel with the possible presence of some nickel oxide. At about 25-30% Cr a predominantly chromium oxide scale is... 

These batteries are new systems which use a lithium-manganese composite oxide for the active material of the positive electrode a lithium-titanium oxide with a spinel... 

The spinel family of oxides with composition AB2O4 has the A and B cations distributed in octahedral and tetrahedral sites in a close-packed oxygen structure (Supplementary Material SI). Impurity doping can take place by the addition of a dopant to octahedral or tetrahedral sites. In this, the spinel family of compounds is quite different from the A2B04 perovskite-related phases of the previous section in that both cation sites are similar in size and can take the same cations. 

The normal spinel Li[Ti2]04 is a metallic oxide with a superconducting transition temperature of 13.7 K. The nominal formula is Li+[Ti3+Ti4+]04, in which the Li+ ions occupy the tetrahedral sites while the octahedral sites contain titanium with an average charge Ti3 5+, although as the material is metallic at room temperature the electrons are delocalized in a partly filled 3d band. 

The electrical conductivity requirement for interconnect applications necessitates the use of chromia-forming (or Cr-rich spinel) oxidation-resistant alloys. One drawback of the chromia-forming alloys for this particular application, however, is the Cr volatility of the chromia or Cr-rich scale. As indicated by many studies [185-189], during high-temperature exposure Cr203 (s) reacts with 02 via the following reaction... 

Also, other metal oxide coatings are possible, for example, electrochemically deposited manganese dioxide. Moreover, further electrocatalytically active oxides are research objectives, for example, oxides with spinel structure such as CoMu204 [36]. 

Figure 8. Formation energy versus Li concentration for three structures of Mn oxide (top) and Co oxide (bottom) ( ) 5-LiJM204-labeled spinel, (0) 7-LiJMn02-labeled layered, and (+) partially inverse spinel structure with 1/4M tetrahedral (ps-(LiJM)tet(LijM3)oct08 0 < x< 1 and 0 < y < 2) labeled 1/4 Mn tet. As the Li content is increased, the Li is added to the tetrahedral site first of p5-(LiJM)ter (LijM3)octOs, and then to the octahedral sites. For Mn, there also is the energy of (a) a structure with one-sixth of the Mn in tetrahedral sites at Xu =1/3 labeled 1/6 Mn tet with a triangle data point and (x) a structure with one-eighth of the Mn in tetrahedral sites at Xu =1/4 labeled 1/8 Mn tet.

Ottonello G. (1986). Energetics of multiple oxides with spinel structure. Phys. Chem. Minerals., 13 79-90. 

Studies of Superconducting Oxides with the Spinel Structure... 

Aluminum forms mixed oxides with many other metals which either replace Al3+ in octahedral positions or occupy tetrahedral sites. The spinel structure of MgAl204, an important prototype, has been investigated by photoelectron spectroscopy.122 Vibrational and solid state NMR methods are also useful for studying aluminate structures.12 125... 

Spinel oxides are important industrial catalysts, possessing good thermal and chemical stability and an ability to maintain catalytic activity at high temperatures. The study reported here is concerned with the properties ofZn(II)-Cr(III) spinel oxides prepared from a carbonate containing LDH precursor. For this study the spinel oxide was separated, by treatment with dilute mineral acid, from the oxide mixture (ZnO and ZnC O, ) obtained by the thermal decomposition of LDH. For comparison, Zn(II)-Cr(lII) spinel oxides were also prepared by more standard synthesis methods. Structural and textural properties were evaluated, using PXRD, TG/MS, FT-IR and N2 adsorption. 

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