Trivalent elements

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,... 

Oxygen and any other divalent elements present are ignored. Any other monovalent elements present, such as halogens, are treated as hydrogens, any other tetravalent elements (e.g. Si) as carbons. If other trivalent elements are contained in the molecules (this is rather unlikely for most organic molecules, but trivalent phosphorus is one example) they are treated as nitrogens. 

Here, other monovalent elements than hydrogen (F, Cl, Br, I) are counted as hydrogens , other trivalent elements such as phosphorus are counted as nitrogen and tetravalent elements (Si, Ge) are handled the same way as carbons. 

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 ... 

It is well known that the elements in framework of zeolite molecular sieves greatly influence the properties and behaviors of these materials [1-3], The introduction of heteroatoms into the framework has become one of most active fields in study of zeolites. The investigations were mostly focused on the methods to introduce heteroatoms into the framework (for examples, hydrothermal synthesis and post-synthesis), the mechanisms for incorporations, the effect of heteroatoms on the acid-base properties and the catalytic features of modified samples [1-10]. Relatively less attention was paid to the effect of treatment process on the porous properties of samples although the incorporation of heteroatoms, especially by the so-called post-synthesis, frequently changes the distribution of pore size. Recently, we incorporated Al, Ga and B atoms into zeolites (3 by the post-synthesis in an alkaline medium named alumination, galliation and boronation, respectively. It was found that different trivalent elements inserted into the [3 framework at quite different level. The heteroatoms with unsuitable atom size and poor stability in framework were less introduced, leading to that a considerable amount of framework silicon were dissolved under the action of base and the mesopores in zeolite crystal were developed. As a typical case, the boronation of zeolites (3 and the accompanied formation of mesopores are reported in the present paper. 

The compositions of samples obtained from chemical analysis are listed in Table 1. If aluminum in the samples are not lost during the boronation ( i.e., the non-framework aluminum species in the parent sample are reinserted into the framework in alkaline medium, which has been proved to be possible in our previous work [12,13]), the change in Si/Al ratios of the boronated samples as shown in Table 1 should be caused by the removal of silicon from the framework. The values of A(Si/Al) in Table 1 represent the number of dissolved silicon (expressed as Si atom/Al atom). For the boronated samples, A(Si/Al) ratios are much greater than B/Al ratios, indicating that the number of boron atoms inserted into the framework is much less than that of removed silicon atoms. In other words, a number of vacancies resulted from silicon removal are not filled by trivalent elements and remain in the framework, consistent with our observation that the masses of the samples decrease after the boronation. It can also be deduced that the vacancies and defects are more in [B]-Na(3-2 than in [B]-Na[3-1 because the A(Si/Al) value of the former is greater than that of the latter. 

For the trivalent elements As, Sb, and Bi, all compounds with the composition X M(R2Dtc)3- (n = 0, 1,2 X = Cl, Br, I) have been obtained. Furthermore, organoantimony(III) derivatives of the type RSb(R2Dtc)2 and R2Sb(R 2Dtc) also have been reported (450a). 

The use ofhydrothermal-like synthesis for the preparation of Mo/V/Al/O catalysts, starting from Anderson-type polyoxometalates, leads to monophasic crystalline compounds, also containing other trivalent elements (Fe, Ga), and dopants [13]. For example, the incorporation of Ti in Mo/V/Al/O gives rise to the formation of a compound having stoichiometry Mo6V2Al1Ti0 5Ox, in which the addition of Ti improves the activity with respect to the undoped system. 

Accordingly, Du increases with both the concentration of the neutral solvation agent, E, initially present in the organic phase, and that of the mineral anion, A-, initially present in the aqueous phase. Inversely, the back-extraction of the trivalent element is favored by a decrease of the concentration of A- in the aqueous solution. 

If the source of anions A is a mineral acid, a competitive proton-extraction reaction might occur, which will decrease the affinity of the neutral solvation agent for the target trivalent elements ... 

The SETFICS process (Solvent Extraction for Trivalent /-elements Intragroup Separation in CMPO-Complexant System) was initially proposed by research teams of the former Japan Nuclear Cycle Development Institute (JNC, today JAEA) to separate An(III) from PUREX raffinates. It uses a TRUEX solvent (composed of CMPO and TBP, respectively dissolved at 0.2 and 1.2 M in -dodecane) to coextract trivalent actinides and lanthanides, and a sodium nitrate concentrated solution (4 M NaN03) containing DTPA (0.05 M) to selectively strip the TPEs at pH 2 and keep the Ln(III) extracted by the TRUEX solvent (239). However, the DFs for heavy Ln(III) are rather poor. An optimized version of the SETFICS process has recently been proposed as an alternative process to extraction chromatography for the recovery of Am(III) and Cm(III) in the New Extraction System for TRU Recovery (NEXT) process. NEXT basically consists of a front-end crystallization of uranium, a simplified PUREX process using TBP for the recovery of U, Np, and Pu, and a back-end Am(III) + Cm(III) recovery step (240, 241). 

Fujii, T., Aoki, K., Yamana, H. 2006. Effect of nitric acid distribution on extraction behaviour of trivalent/-elements in a TRUEX system. Solvent Extraction and Ion Exchange 24(3) 347-357. 

Zeolites [63] are extensively used as shape-selective solid acid catalysts in many industrial processes [64]. Their acidic properties stem from the presence of trivalent elements, such as Al, in the zeolite framework. The strength of these acid sites is one of the main features that determine the catalytic properties of a zeolite catalyst. Substitution of the Al atoms by other trivalent elements, such as Ga, Fe, and B, alters the strength of these acid sites, and hence also the catalytic properties of a zeolite. The possible effect of the partial substitution of the tetravalent Si atoms (which, in principle, do not create acid sites in zeolites) by Ge atoms (also tetravalent) on the catalytic properties of zeolite ZSM-5 [65] is presented here. The idea is that the different electronic and geometric properties of Ge, compared with Si, may influence the acid sites related to the Al atoms, and thereby the catalytic properties of ZSM-5. 

Boron, aluminum and gallium are all highly hydrolysed trivalent elements, but the extent of their hydrolysis in seawater is distinctly different. While all three elements exist as M(OH) and M(OH)4 in seawater, Al is much more weakly hydrolysed than either B or Ga. The free-to-total metal ratio for Al3+ is in the order of 10 9A at 25°C and pH 8.2, while for Ga the free-to-total metal ratio is in the order of 10 15 7. Owing to its high charge and small radius, boron does not form a simple cation (M3+) in aqueous solution and, in fact, forms of boron less... 

The investigation of the substitution cf TiIT for SiIT in the structure of HFI-type zeolites ia in progress. The first reaulta ahow a lower aubstitution degree, similar to the values obtained with the trivalent elements. This probably results from the stability difference between the geraaniua and the titaniua fluorc-coap-lexea. 

The complete or partial cancelling by F of the negative charges induced by the incorporation of trivalent elements auch as A1 influ-... 

The same order holds for the decomposition of the sulphates those of the trivalent elements aluminium and iron decompose relatively easily, those of the alkaline earth metals decompose appreciably on heating to redness (thus CaS04 decomposes quantitatively on ignition in the blowpipe flame, barium sulphate only a little), the alkali sulphates are stable. That the free acids are much less stable than most of the salts is understandable when we regard the hydrogen ion as an extremely small positive ion. 

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