Host oxides

Host microorganisms, for industrial enzyme production, 10 264-265 Host oxide lattice structure, 19 403 Hot air food driers, 12 85 Hot and cold composite curves, 13 222 Hot-box resins, 12 273 Hot briquetted iron (HBI), 14 492-494, 509 21 412... 

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The color of mixed-metal oxide pigments results from the incorporation of chromophores, into the structure of stable host oxides. 

The use of metal nitrates provides a particularly convenient method for doping a host oxide with luminescent ions. Along with the yttrium nitrate, a luminescent rare earth ion such as Eu3+, can be added as a nitrate salt. In addition to yttria, alumina can also be prepared from aluminum nitrate and hydrazine (Ozuna et al., 2004) ... 

Tungsten and molybdenum bronzes, AxW03 and AxMo03 (As k, Rb, Cs) are generally prepared by reaction of the alkali metals with the host oxide. Electrochemical methods are also employed for these preparations. A novel reaction that has been employed to prepare bronzes which are otherwise difficult to obtain involves the reaction of oxide host with anhydrous alkali iodides [49] ... 

The color of complex inorganic pigments results from the incorporation of cations of transition metals into the crystal of the host oxides. The host can be a single oxide such as Ti02 (rutile) or a mixed oxide such as TiZn204 (spinel) or MgAl204 (spinel). Most of the host oxides can be found as naturally occurring... 

The host oxide lattice, moreover, is able to be reduced by spiltover hydrogen, producing water. Spillover induces lower temperatures of reduction for vanadium, uranium, chromium, cobalt, cadmium, and tin oxides (127), among others. The reduction may involve bulk transformation or it may be confined to the surface. The most studied example of this phenomena involves Ti02 and the resultant changes in sorption capabilities of the surface (SMSI), as discussed above. SMSI seems to be an extreme example of the change in chemisorptive properties with reduction and subsequent occulta-tion of the supported metal. 

It has been shown in the previous sections that the addition of small amounts of a transition metal to various metal oxides lowers the temperature required for their reduction by H2. This phenomenon has been attributed to hydrogen spillover. It follows that a partial reduction of the host oxide can induce or modify the catalytic activity of the host material. 

Alkali metal intercalation reactions have been intensively studied for systems involving lithium. Host oxides are those of elements in high oxidation states that possess lower valence states that are also stable in oxides. Lithium intercalation may be carried out by Lil solutions for easily reducible systems, for example. 

It is therefore advisable to use the doping elements in quantities compatible with complete solubility in the host oxide, and to check that they do not segregate during the catalytic reaction. Cobalt, mentioned above as a useful dopant, could exert a catastrophic effect if segregated as cobalt oxide, because of the high activity of the latter in complete oxidation. 

When cationic guest atoms such as lithium, hydrogen, and sodium reversibly enter or leave the host oxide crystal, along with an accompanying electron flow but without any change in crystal structure, the reaction is referred to as intercalation/ deintercalation as follows [1, 2] ... 

The catalytic synthesis of C2H4 directly from CH4 has been examined in the presence of oxygen for many metal oxides containing alkali metal salts. Addition of alkali halides onto metal oxides depressed the catalytic activities of the host oxides in deep oxidation of CH4, but favorably enhanced the direct synthesis of C2H4 from CH4, Among the catalysts tested, the oxides of Mn and Ni with LiCl produced ethylene with high selectivity (ca. 60%) and yield (ca. 27%). The role of alkali halides for the selective synthesis of C2H4 was examined for LiCl-added NiO. It is speculated that the alkali metals incor-... 

Powder metal oxides were used as the host oxides for alkali metal additives. The oxides with salts of alkali metals (chlorides, nitrates, carbonates, etc.) were prepared by impregnation method using aqueous solutions of the salts. The content of the alkali metal was adjusted to 20 mol% for each... 

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