Polyvalent cations, selectivity

Nevertheless, it is useful to point out that zeolites with higher framework Si content generally prefer larger, less hydrated cations (e.g. Cs with its smaller hydrodynamic radii), while those with Si/Al 1 take up hydrated polyvalent cations selectively. The role of water is apparent here and also with the growing realization that water in immediate contact with an aluminous zeolite surface is hydrolyzed with two foreseeable consequences ... 

The catalytic activity Z -5 -Jype. zeolitesmodified by polyvalent cations (Ca, Mg, x, In, Dy, So, Ga, A1, Be ), were investigated in reactions of toluene al lation by ethylene and transalkylation of ethylbenzene. The presence in these samples of aprotic acid centres of different strength and absence of prot-ic centres were established by IR spectroscopy technique of adsorbed CO. The strength of aprotic centres was characterized by the heat of CO adsorption and was shown to be a main factor determining the selectivity of catalytic action of the systems studied. 

Fortunately, strong acid resins are selective for polyvalent cations in dilute... 

The potential of liquid-membrane electrodes develops across the interface between the solution containing the analyte and a liquid-ion exchanger that selectively bonds with the analyte ion. These electrodes have been developed for the direct potentiometric measurement of numerous polyvalent cations as well as certain anions. 

U.S. 4551330 (1985) Wagman et al. (Helene Curtis) Oil-in-water emulsion inverts to water-in-oil emulsion at the hair surface when being rubbed onto the hair unctuous oleaginous water-dispersible polyvalent metal salt having a cation selected from Al3+, Ce3+, F3 , Zr4+, and aluminum zirconium coordination complex acid or alkali to give pH 1.5-7.5... 

A1r Separation Properties. Self-bound LSX adsorbents have an enhanced ability to selectively adsorb nitrogen from air. For thermodynamically driven adsorption processes, the quantity of a gas adsorbed by a zeolite at a given pressure and temperature Is a function of Its the affinity for the cationic adsorption sites as well as the quantity of sites available for Interaction. Electronic charge balance dictates that the LSX will have the maximum number of cationic sites available for direct Interaction with weakly Interacting adsorbates. The electric field within the zeolite cavity 1s dependent on both structure and the charge density of the extra-framework cation. Small polyvalent cations 1n the dehydrated/dehydroxylated state, especially calcium, show high selectivity for N2 from a1r.(l2)... 

To maintain solvent capacity for uranium and to prevent contamination of extracted uranium by iron, it is necessary to reduce iron to the unextractable ferrous condition before solvent extraction. This is done by contacting the leach liquor with scrap iron, SO2, or sodium sulfide. Because the iron content of leach liquor is high, reduction is costly, and the Amex process, in which ferric iron does not extract, is preferred for sulfuric acid leach liquors. The high distribution coefficient of other polyvalent cations such as Th and in EHPA makes the Dapex process less selective for uranium than the Amex process. 

Porous structure is not the only factor that must be taken into account in order to reach a high selectivity to Cj-Cg olefins. High selectivities for light paraffins, principally propane, can be observed on small-pore zeolites. The reduction of the concentration of acid sites, responsible for hydrogen transfer reactions, decreases the conversion of olefins to paraffins. The principal methods that can be used to reduce the concentration of these strong acid sites in zeolites are dealumination, cation exchange, and isomorphous substitution of Al cations by polyvalent cations. 

Another method to produce more stable cracking catalysts is the introduction of polyvalent cations into, e.g., Na-Y, in particular La or rare earth (RE) cations [435,436]. Hirschler [437] andPlank [438] independently suggested that formation of OH groups via introduction of polyvalent cations is due to the following chemistry (which is nowadays generally referred to as the Hirschler-Plank mechanism), illustrated here with two selected examples using chlorides of two- or three-valent cations, M" and M ", respectively ... 

Naturally, aU metal chlorides elute before hydrochloric acid. When judging by the values of BtVo.os under similar conditions, the separation selectivity of FICl from metal chlorides increases slightly on all tested sorbents in the series K" " < Na < Li < Ca, along with the increase of the radius of the hydrated cations. In combination with the larger anion S04 - (Vdr = 3.79A), only polyvalent cations have a chance to significantly contribute to the separation. Indeed, Cu(II), Fe(II), and Al(III) sulfetes readily separate from sulfuric acid. Hydrated radii of these cations are estimated as 4.19, 4.28, and 4.75 A, respectively, according to which aluminum has the smallest breakthrough volume. 

The fluoride ion-selective electrode is subject to interference by polyvalent cations, e.g., Ca Fe, and Al, either acting on their own or in combination with other species and a complexant 1,2-di-amino-cyclohexane-N,N,N, N -tetraacetic acid is used to preferentially complex the interfering metal ions. 

To accomplish any separation of two cations (or two anions) of the same net charge, the stationary phase must show a preference for one more than the other. No variation in the eluant concentration will improve the separation. However, if the exchange involves ions of different net charges, the separation factor does depend on the eluant concentration. The more dilute the counterion concentration in the eluant, the more selective the exchange becomes for polyvalent ions. 

There are two general types of liquid-membrane ISEs, namely one which involves liquid-phase ion exchange, with the response being selective to the anion or cation under scrutiny (generally polyvalent ions), while the other type involves... 

Values are quoted relative to the hydrogen ion for cations and to the chloride ion for anions. As shown, selectivity also increases with increasing degree of. cross-linking. At concentrations greater than 0.1 M selectivity for monovalent over polyvalent ions increases. Ionic properties which determine reSin affinity are complex involving hydration energy, polarizability and hydrated ionic radius. The last shows an approximately inverse relationship to the selectivity coefficient. 

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