Alkaline earth oxide

Alkaline-earth Oxides. - The surface chemistry of strongly basic substances like alkaline-earth oxides had received little attention until the early seventies. Studies were mainly concerned with the properties of radiation-damaged samples. Subsequently, from the work of several groups of researchers, in particular the groups at Harwell, Bath, Sapporo, and Turin, there has been a considerable increase in the number of studies involving thermally activated Group II solid bases. The conventional spectroscopies, which are the subject of this review, together with the less common luminescence spectroscopy, 

It is useful to distinguish between molecules containing H atoms and those with no H atoms, because on this depends the involvement or otherwise of the Br nsted basicity of the adsorbent. Cerruti et a/. studied, by i.r., the chemisorption of NO on MgO, and found that this molecule undergoes disproportionation, yielding nitrites (NO of various kinds as oxidized products, and hyponitrites (NjO and possibly NO as reduced 

In the latter three cases the depletion of polymers leads to new species still having some unsaturated character. 

Coluccia, E. Garrone, and E. Borello,/. Chem. Soc., Faraday Trans. 1, in the press. 

Coluccia and A. J. Tench, in New Horizons in Catalysis , Proceedings 7th Int. Congr. on Catalysis, Tokyo, 1980, ed. T. Seiyama and K. Tanabe, Elsevier, Amsterdam, 1981, Part B, p. 1154. 

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Historically an earth was a non-metallic substance, nearly insoluble in water and unchanged on heating. The alkaline earth oxides, e.g. CaO, have an alkaline reaction in addition to being clearly earths . 

Within the periodic Hartree-Fock approach it is possible to incorporate many of the variants that we have discussed, such as LFHF or RHF. Density functional theory can also be used. I his makes it possible to compare the results obtained from these variants. Whilst density functional theory is more widely used for solid-state applications, there are certain types of problem that are currently more amenable to the Hartree-Fock method. Of particular ii. Icvance here are systems containing unpaired electrons, two recent examples being the clci tronic and magnetic properties of nickel oxide and alkaline earth oxides doped with alkali metal ions (Li in CaO) [Dovesi et al. 2000]. 

Direct attack by hot 70—80 wt % hydrofluoric acid, sometimes with nitric acid (qv), is effective for processiag columbites and tantalo-columbites. Yields are >90 wt%. This method, used in the first commercial separation of tantalum and niobium, is used commercially as a lead-in to solvent extraction procedures. The method is not suited to direct processiag of pyrochlores because of the large alkaU and alkaline-earth oxide content therein, ie, ca 30 wt %, and the corresponding high consumption of acid. 

Heterogeneous Catalytic Polymerization. The preparation of polymers of ethylene oxide with molecular weights greater than 100,000 was first reported in 1933. The polymer was produced by placing ethylene oxide in contact with an alkaline-earth oxide for extended periods (61). In the 1950s, the low yield and low polymerization rates of the eady work were improved upon by the use of alkaline-earth carbonates as the catalysts (62). 

Fused basic salts and basic oxides react with vitreous siUca at elevated temperatures. Reaction with alkaline-earth oxides takes place at approximately 900°C. Hahdes tend to dissolve vitreous siUca at high temperatures fluorides are the most reactive (95). Dry halogen gases do not react with vitreous siUca below 300°C. Hydrogen fluoride, however, readily attacks vitreous siUca. 

The resistance of graphite to thermal shock, its stabiUty at high temperatures, and its resistance to corrosion permit its use as self-supporting vessels to contain reactions at elevated temperatures (800—1700°C), eg, self-supporting reaction vessels for the direct chlorination of metal and alkaline-earth oxides. The vulnerabiUty of cemented joints in these appHcations requires close tolerance ( 0.10 mm) machining, a feat easily accompHshed on graphite with conventional metal machining equipment. 

Turning to non-metallic catalysts, photoluminescence studies of alkaline-earth oxides in dre near-ultra-violet region show excitation of electrons corresponding to duee types of surface sites for the oxide ions which dominate the surface sUmcture. These sites can be described as having different cation co-ordination, which is normally six in the bulk, depending on the surface location. Ions on a flat surface have a co-ordination number of 5 (denoted 5c), those on the edges 4 (4c), and dre kiirk sites have co-ordination number 3 (3c). The latter can be expected to have higher chemical reactivity than 4c and 5c sites, as was postulated for dre evaporation mechanism. 

An effect which is frequently encountered in oxide catalysts is that of promoters on the activity. An example of this is the small addition of lidrium oxide, Li20 which promotes, or increases, the catalytic activity of dre alkaline earth oxide BaO. Although little is known about the exact role of lithium on the surface structure of BaO, it would seem plausible that this effect is due to the introduction of more oxygen vacancies on the surface. This effect is well known in the chemistry of solid oxides. For example, the addition of lithium oxide to nickel oxide, in which a solid solution is formed, causes an increase in the concentration of dre major point defect which is the Ni + ion. Since the valency of dre cation in dre alkaline earth oxides can only take the value two the incorporation of lithium oxide in solid solution can only lead to oxygen vacaircy formation. Schematic equations for the two processes are... 

Because all of the alkaline earth oxides react with water to form basic hydroxides, they are called basic oxides. The reactions and their heats are as follows ... 

Alkaline earth oxides, heat of reaction with water, 382 Alkaline earth sulfates, K,r, 382 Alkanes, 341 naming, 338 Alkyl group, 336 Alloys, 309 Alnico, 406 copper, 71, 309 covalent bonds, and, 305 gold, 71... 

The Alkaline-Earth Oxides, etc.—The observed and calculated inter-atomic distances for the alkaline-earth oxides, sulfides, selenides and tellurides are given in Table VIII. Except for the magnesium com-... 

Alkaline-Earth Oxides, etc., with the Sodium Chloride Structure... 

Carbonate mineralisation refers to the conversion of C02 to solid inorganic carbonates. Naturally occurring alkaline and alkaline-earth oxides read chemically with C02 to produce... 

Data for ionic oxides (alkaline earth oxides) are presented in Chapter 11, although they could be presented in this chapter since they are bonded ioni-cally. The sulfides are closely related, and are presented here. 

Perhaps the most simple crystals in this class are the alkaline earth oxides. They are II-VI compounds and have rocksalt crystal structures. Data for their hardnesses versus their bond moduli (optical band gaps per molecular volumes) are displayed in Figure 11.4. 

Figure 11.4 Hardness of alkaline earth oxides vs. bond moduli.

S. P. Singh, S. Gupta, and S. C. Goyal, Elastic Properties of Alkaline Earth Oxides under High Pressure, Physica B, 391,307 (2007). 

Extensive study has been devoted to paramagnetic defects that are formed on high-surface area alkaline earth oxides, particularly magnesium oxide. The work carried out by Wertz el al. 187, 188) and Henderson and Wertz 139) on bulk defects formed in MgO single crystals has been quite valuable in the identification of the surface defects. Both the bulk and surface defects may be divided into two classes those in which an electron... 

Comparison of promoted alkaline-earth oxide catalysts prepared through evaporation and sol-gel methods by their catalytic performance in propane oxidative dehydrogenation... 

Alkaline earth oxides (AEO = MgO, CaO, and SrO) doped with 5 mol% Nd203 have been synthesised either by evaporation of nitrate solutions and decomposition, or by sol-gel method. The samples have been characterised by chemical analysis, specific surface area measurement, XRD, CO2-TPD, and FTIR spectroscopy. Their catalytic properties in propane oxidative dehydrogenation have been studied. According to detailed XRD analyses, solid solution formation took place, leading to structural defects which were agglomerated or dispersed, their relative amounts depending on the preparation procedure and on the alkaline-earth ion size match with Nd3+. Relationships between catalyst synthesis conditions, lattice defects, basicity of the solids and catalytic performance are discussed. 

Alkaline earth oxides (AEO = MgO, CaO, and SrO) doped with 5 mol% Nd203 were synthesised by both evaporation and sol-gel methods. According to the first method, water solution of nitrates was evaporated under continuous stirring, dried, and nitrate mixture was decomposed at corresponding temperatures (Table 1) for one hour (samples designated Ev). All samples were calcined at 650°C for 3h after the decomposition. In the sol-gel method the samples (designated SG) were obtained... 

Comparison of promoted alkaline-earth oxide catalysts... 

In contrast to MgO, the other alkaline-earth oxides, such as CaO, SrO, and BaO, were found to be poor supports for NiO, as they provided catalysts with low activities, selectivities, or stabilities (Fig. 14) (239). Although the reduced Ni0/Al203 catalyst provided high initial conversions (CH4, 91% C02, 98%) and selectivities (>95% for both CO and H2), it was characterized by the fastest carbon deposition, which led to the complete plugging of the reactor after only 6 h of reaction (197). The reduced Ni/Ti02 catalyst gave relatively low initial... 

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