Mixed oxide formation

It is well known that redox properties of oxides can be modified by the formation of mixed oxides (12). Effect of mixed oxide formation on AG° of M-0 dissociation is illustrated in Figure 1. The free energy changes of the following reactions, AGA° and AGp°, are calculated from thermodynamic data (13, 14). 

Figure 1. Effect of mixed oxide formation on AG° of M-0 dissociation (298 K). Lines 1)—3) show the mixed oxide systems based on CoO, ZnO, and Ti02, respectively, a) - d) are - aGr for the following reactions.

It is now possible to consider the ternary tin-antimony-oxygen system. It would be reasonable to expect that multiphase systems would predominate in antimony rich materials although there is little information about the solubility of tin in antimony oxide. Since the metal-oxygen bond lengths in tin(IV) and antimony(V) and (III) oxides are all similar 26, 29), it is reasonable to expect that mixed oxide formation by coprecipitation is feasible and would involve the replacement by antimony of tin in the tin(IV) oxide... 

Formation of mixed oxides Formation of ternary oxides or sulfides... 

This compound is measured photometrically at 623 nm. Its blue colour can probably be traced to the mixed oxide formation of the tetravalent and hexavalent molybdenum (Holleman-Wiberg). 

Radiochemical analyses of PWR primary coolant show that the major fraction of the neptunium and plutonium traces in the coolant is usually associated with the corrosion product suspended solids and that it can be removed from the coolant by filtering. Only in cases of very low corrosion product concentrations in the coolant were significant proportions of the transuranium elements observed to be present in a dissolved (i. e. non-filtrable) form. As yet, it is not known whether mixed oxide formation between magnetite-type oxides and these elements is responsible for this behavior or whether the actinide traces are adsorbed by van de Waals forces onto the large surface areas of the finely dispersed suspended solids. Under constantload operation conditions and as long as no additional fuel rod failures occur, the activity ratio Pu Co in the corrosion products remains virtually constant over time, thus indicating a similar behavior of these different elements in the coolant. 

Monitoring the in situ IR and Raman spectra of LDHs under heating has also provided valuable insight into the LDH decomposition process and the ensuing mixed oxide formation (307,308 see also Sec. V.C). 

Application of LDHs is mostly based on their use after thermal treatment and mixed oxide formation. If the calcination is performed at temperatures below 550 °C, mixed oxides also have, besides the aforementioned properties, the memory effect. This very specific property of mixed oxides derived from thermal degradation of LDHs allows the reconstruction of the layered structure in mild conditions when mixed oxides are in contact with aqueous solution or air. If calcination is carried out at temperatures above 827 °C, irreversible mixed spinels are formed and the memory effect is disabled [48]. The main application of the memory effect is for the synthesis of LDHs with different interlayer anions than CO ". Taking to consideration that carbonate anions have the highest affinity toward the incorporation in the LDH interlayer, during the classical synthesis methods the contamination with carbon dioxide from the air always occurs. If, for example, the synthesis LDH with OH" ions in the interlayer is required, the reconstruction of mixed oxides can be performed by steam or contact with decarbonized water. Similarly, if synthesis of LDHs with other anions in the interlayer is anticipated, reconstruction is carried out in an aqueous solution containing the desired anions. Catalytic properties of mixed oxides obtained by reconstruc-tion/recrystallization procedure depend mainly on the conditions of each activation step. 

Only thallium of the Group III elements is affected by air at room temperature and thalliumflll) oxide is slowly formed. All the elements, however, burn in air when strongly heated and, with the exception of gallium, form the oxide M2O3 gallium forms a mixed oxide of composition GaO. In addition to oxide formation, boron and aluminium react at high temperature with the nitrogen in the air to form nitrides (BN and AIN). 

When the host is a mixed oxide, the incorporation of the chromophore is best achieved during high temperature formation from single oxides ... 

II. Thiol oxidants cystaminc (mixed disulfide formation), diamide, t-BHP, menadione, diquat... 

The present work demonstrates that the mixed oxide catalyst with inhomogeneous nanocrystalline MosOu-type oxide with minor amount of M0O3- and Mo02-type material. Thermal treatment of the catalyst shows a better performance in the formation of the crystals and the catalytic activity. The structural analysis suggests that the catalytic performance of the MoVW- mixed oxide catalyst in the partial oxidation of methanol is related to the formation of the M05O14 t3 e mixed oxide. 

Due to the formation of Ca/Al mixed oxide on the surface, the Ca -modified alumina has a completely different structure compared to the spinel one This leads to a different type of surface Lewis acid/basic sites, rendering the catalyst 30 times less active. 

This chapter reports about an investigation on the catalytic gas-phase armnoxidation of u-hexane aimed at the production of 1,6-Ce dinitriles, precursors for the synthesis of hexamethylenediamine. Catalysts tested were those also active and selective in the ammoxidation of propane to aciylonitrile mtile-type V/Sb and SnA /Nb/Sb mixed oxides. Several A-containing compounds formed however, the selectivity to cyano-containing aliphatic linear Ce compounds was low, due to the relevant contribution of side reactions such as combustion, cracking and formation of heavy compounds. 

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