For sodium-exchanged

Unit Cell TABLE IV Data For Sodium Exchanged Samples of ZK4... 

For N adsorbed on Alaskan mordenite, the chemical shift dispersion from the chemical shift anisotropy is reduced to about 190 ppm and so = 0.31. For sodium-exchanged Zeolon -0jl>= 90 ppm and = 0.19. From Equation 6, and assuming that f1 of the adsorption sites are similar for the two zeolites, we estimate that the contribution of fe-q is about twice as large for the Alaskan mordenite as for HB33. 

If the solution is buffered so [H ] is constant, the equation above for sodium exchange or adsorption is similar to the Langmuir isotherm. 

Water is softened by removing calcium and magnesium ions from hard water in exchange for sodium ions at sites on cation-exchange resin. Water softeners typically use a gel polystyrene sulfonate cation-exchange resin regenerated with a 10% salt brine solution (25). 

Ion exchangers are sometimes used on a throwaway basis also. In the laboratoiy, ion exchangers are used to produce deionized water, purify reagents, and prepare inorganic sols. In medicine, they are used as antacid, for sodium reduction, for the sustained release of drugs, in skin-care preparations, and in toxin removal. 

Zeolites are naturally occurring hydrous aluminum-sodium silicates in porous granule form. They are capable of exchanging their sodium base for calcium or magnesium and of expelling these alkaline earth metals for sodium by treatment with salt. Thus, they are a type of ion-exchange media. (Some zeolites act as molecular sieves by adsorption of water and polar compounds.)... 

Streitweiser et al.597 have also measured second-order rate coefficients for hydrogen exchange of fluorobenzenes with sodium methoxide in methanol, Table 182. Nucleophilic displacement of fluoride ion by methoxide ion accompanies... 

Carbonic anhydrase is an enzyme that produces free hydrogen ions, which are then exchanged for sodium ions in the kidney tubules. Carbonic anhydrase inhibitors inhibit the action of the enzyme carbonic anhydrase This effect results in the excretion of sodium, potassium, bicarbonate, and water. Carbonic anhydrase inhibitors also decrease the production of aqueous humor in the eye, which in turn decreases intraocular pressure (IOP) (ie, the pressure within the eye). 

Second, bromination of methyl groups attached to arylphenoxy-phosphazene polymers converted them to CH2Br units (22). These were then quaternized with triethylamine, and the quaternary sites were used for anion exchange with sodium heparin (Fig. 2). The... 

Ion exchange zeolites are builders in washing powder, where they have gradually replaced phosphates to bind calcium. Calcium and, to a lesser extent, magnesium in water are exchanged for sodium in zeolite A. This is the largest application of zeolites today. Zeolites are essentially nontoxic, and pose no... 

A composite polymer membrane has also been used as an effective amperometric detector for ion exchange chromatography [42] and showed detection limits similar to those obtained with a conductivity detector. An advantage of the amperometric detector based on micro-ITIES over the conductometric detector is that selectively can be tailored by proper choice of the ionophore. For instance, the selectivity of the membrane toward ammonium in the presence of an excess of sodium could be substantially increased by introducing an ammonium-selective ionophore (such as valinomycin) in the gel membrane [42]. 

Various polyphosphates are effective sequestering agents under appropriate conditions. The best known of these is sodium hexametaphosphate (10.14), the cyclic hexamer of sodium orthophosphate. Further examples are the cyclic trimer sodium trimetaphosphate (10.15), as well as the dimeric pyrophosphate (10.16), the trimeric tripolyphosphate (10.17) and other linear polyphosphates (10.18). All of these polyanions function by withdrawing the troublesome metal cation into an innocuous and water-soluble complex anion by a process of ion exchange as shown in Scheme 10.7 for sodium hexametaphosphate. Hence these compounds are sometimes referred to as ion-exchange agents. 

Aerosil was converted into the sodium form by treating it with a buffer solution (pH = 8.4) made of sodium hydroxide and sodium hydrogen carbonate solutions, after which it was filtered, washed free of alkali, and dried. This sodium-exchanged aerosil was then suspended in a solution of Ni(en)3(N03)2 prepared by adding the calculated amount of ethylene-diamine to a solution of nickel nitrate. The suspension was agitated for about 30 min and filtered off. The catalyst was then washed and dried at 100°C. 

The higher intensities /3 measured for ion exchanged gels (gels prepared by procedure b) comparing to /3 of gels prepared by procedure a, are probably the result of the different silica source used. It was found that gels prepared from sodium silicate contain... 

Adsorption enthalpies and vibrational frequencies of small molecules adsorbed on cation sites in zeolites are often related to acidity (either Bronsted or Lewis acidity of H+ and alkali metal cations, respectively) of particular sites. It is now well accepted that the local environment of the cation (the way it is coordinated with the framework oxygen atoms) affects both, vibrational dynamics and adsorption enthalpies of adsorbed molecules. Only recently it has been demonstrated that in addition to the interaction of one end of the molecule with the cation (effect from the bottom) also the interaction of the other end of the molecule with a second cation or with the zeolite framework (effect from the top) has a substantial effect on vibrational frequencies of the adsorbed molecule [1,2]. The effect from bottom mainly reflects the coordination of the metal cation with the framework - the tighter is the cation-framework coordination the lower is the ability of that cation to bind molecules and the smaller is the effect on the vibrational frequencies of adsorbed molecules. This effect is most prominent for Li+ cations [3-6], In this contribution we focus on the discussion of the effect from top. The interaction of acetonitrile (AN) and carbon monoxide with sodium exchanged zeolites Na-A (Si/AM) andNa-FER (Si/Al= 8.5 and 27) is investigated. 

The ZSM-5 zeolite had a SAR (silica-to-alumina ratio) value of 38 and were supplied by CENPES/PETROBRAS. These samples, as received, were submitted to two ion exchange processes with ammonium chloride solution at 323K for sodium content reduction, followed by calcinations at 773K under dry air flow for transformation to its acid form. 

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