Trivalent element oxides

In our design, divalent Ca was chosen to partially substitute the trivalent atoms, and La and Ce were selected for a trivalent element because their ionic size (rLas+ = l.SOA rce3+=l-48A) was close to that of Ca (rca2+ = T48A) [21]. Like La, the Ce element also generally shows a formal -i-3 oxidation state in in-termetallics. Erom the reactions of the elements, we have identified as major phases the electron-precise/deficient alloys, Ln5.xCaxGe4 (Ln=La, Ce x=3.37,... 

The rare earth metals. The rare earth metals are extremely reactive elements especially with respect to the normal atmospheric gases. The light trivalent lanthanides oxidize with air at room temperature they should be stored (and handled) in vacuum or under He or Ar. Divalent Eu oxidizes much more readily than any of... 

The problem of the role of acidity in the oxidation reaction has been examined. To this end silicalites containing both Ti(IV) and Al(III),- or Fe(III) or Ga(III) have been synthesized [24-26] and used in the epoxidation of propylene. It is well known that trivalent elements introduced in the framework impart definite acidic character to the material. The results obtained under very similar experimental conditions are given in Table 2. 

Substituting divalent or trivalent elements for the A1 in the framework has been successfully carried out by several groups yielding novel heterogeneous catalysts (metal-substituted ALPOS, MALPOs Thomas et al 2001) for hydrocarbon oxidation and liquid phase oxidation. MALPO catalysts can be complementary to metal-doped silicalite catalysts. Particularly interesting compounds are MALPOs in which a divalent metal (Me) substitutes for the framework Al +, for example MALPO-36 (where M = Mg, Mn, Zn, Co) and MALPO-34 (M = Mg, Mn, Co etc). 

Physical Properties. Zinc oxide is a fine white powder that turns yellow when heated above 300 °C. It absorbs UV light at wavelengths below 366 nm. Traces of monovalent or trivalent elements introduced into the crystal lattice impart semiconducting properties. The elementary particles of ZnO obtained by the thermal method may be granular or nodular (0.1-5 pm) or acicular (needle-shaped). Some physical properties are given below ... 

As a metal, europium is very reactive so that one usually finds it under its trivalent, triply oxidized form (Eu3+ ion) in oxides or salts. A divalent form (Eu2+) also displays some stability. Two minerals that contain many of the lanthanide elements, which are separated by liquid-liquid extraction, are commercially important monazite (found in Australia, Brazil, India, Malaysia, and South Africa) and bastnasite (found in China and the United States). 

Mendeleev drew five important conclusions from these rare-earth accommodations. The first one concerned the oxidation states of the rare-earth elements. Lanthanum, a typically trivalent element, was placed... 

Beryllium, Be = 9, is undoubtedly a divalent rare-earth element, with the oxide RO, as was shown by the author in 1878, 1881, and 1882. Then come the trivalent elements scandium. Sc = 44 yttrium,... 

Oxides of Trivalent Elements and Spinel-Type Structures... 

The so-called beta-aluminas are characterized by the existence of layered blocks of a trivalent element (most frequently AT, but also Fe " and Ge ) with the same spinel structure separated by mirror planes where large monovalent (Na or K), divalent (Ba, and sometimes Ca or Sr) and trivalent (La) cations, which do not enter the cubic close packed array of oxide ions of the spinel blocks, are located, together with oxide anions bridging between the blocks. In these planes the cations... 

In 1872 Mendeleeft pointed out that there was no place in the Periodic Table for a trivalent element of atomic weight 120, and drew attention to the similarity of uranium to chromium, molybdenum, and tungsten he therefore suggested that the atomic weight should be doubled, so that uranium could be placed below these elements in the table. He also formulated the oxides, by analog with those of the other elements in the group, as follows uranous oxide UOg, urano-... 

The hydroxide, M(OH)3, oxyhydroxide, MO(OH), and oxide, M2O3, of A1 (and certain other trivalent elements) exist in a and 7 forms. We give the mineral names of these A1 compounds because they are often referred to by name and also because the American nomenclature is sometimes different from that used in England. 

As can also be observed in Table 2 the product distribution is different for TS-1 and Ti-Beta catalysts during the oxidation of olefins. While TS-1 gives almost selectively the epoxide, Ti-Beta produces the corresponding monoalkylglycolethers. This is explained on the basis of the acid sites associated to the presence of Al in Ti-Beta which catalyze the opening of the epoxide ring. Indeed, this also occurs in TS-1 when trivalent elements, such as Al, Ga, or Fe are introduced in the framework... 

Due to the recent discoveries of the rare-earth elements, most of their chemical and physical properties were stUl shrouded in mist at the beginning of 1869, and Mendeleev had to manage with the limited information he had at his disposal. At the time, Mendeleev stUl adhered to the old Berzelian atomic weights for the rare-earth elements. Not one of these values corresponded to the real atomic weights however, as they were based on the erroneous assumption that most rare-earth elements were bivalent instead of trivalent Their oxides were thus represented by the formula RO (with the higher oxide of cerium denoted as R2O3). 

The discovery of scandium excited the scientific community and Nilson s compatriot P. Cleve set out to study the newly discovered element. He studied it thoroughly for almost five months and came to the conclusion that many results obtained by Nilson were erroneous. Cleve reported to the Paris Academy of Sciences on August 18, and the academicians learnt much new about scandium. It turned out to be trivalent its oxide s formula was ScjOa its properties differed somewhat from those determined by Nilson. According to Cleve (and this was especially important)... 

A similar approach can be taken in comparing the sesquioxides of both series, although some approximations must be considered (Templeton and Dauben 1957) in deriving radii from the sesquioxide lattice parameters. Radii based on these sesquioxides have also been compiled by others (Shannon 1976, Haire and Baybarz 1973). Trivalent radii for these f-element oxides are given in table 30. Radii and cubic lattice parameters are also plotted in fig. 18. Based on such radii, it can be seen that the... 

The solid-state reaction between HZSM-5 and iron compounds (FeO, Fe304, FeCl3) was investigated by Kucherov and Slinkin [171]. The formation of isolated extra-framework Fe + species was observed only in samples treated with FeCl3, while no migration of the trivalent element within the porous structure was observed after high temperature treatment with iron oxides. Similar results were obtained by Wichterlova et al. [172]. 

Members of the columbite-tantalite family of minerals also often contain significant U along with rare earths, Fe, Ca and Th. The B site is either Nb or Ta. Like the pyrochlores, these minerals are associated with rare-earth pegmatites and are also known from placer deposits. Most of the compounds probably formed initially with U —most probably as a coupled substitution Ca -t-U for a trivalent ion. Oxidation occurs easily, however, and most specimens contain significant amounts of U. Those minerals which contain radioactive elements are usually metamict and require heating to develop crystallinity. 

We have synthesized silicalites containing both Ti and a trivalent element (Al, Ga, Fe) in lattice position. Syntheses are similar to that of TS-1. As we add increasing aunounts of a trivalent metal nitrate to the reaction mixture, we obtain silicalites containing both titanium and the other metal. Titanium content decreases with increasing content of the trivalent metal. Physico-chemical analyses (e.g., XRD, FT-IR, EPR, MAS-NMR, exchange capacity) and oxidizing and acidic catalytic activities confirmed isomorphous substitution of both elements. 

Several patents claimed also the synthesis of zeolites containing both titanium and a trivalent element (ref.s 4,5). However only in few of them proofs about the presence of )30th elements in lattice position are given (ref. 5). The presence of Ti and Al (or Ga, or Fe) in lattice position can give rise to catalysts possessing a good activity in both oxidizing and acid catalyzed reactions. 

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