Ion exchange forms of zeolite

Ion-Exchanged Forms of Zeolite L, Erionite, and Offretite and Sorption of Inert Gases... 

It was also of interest to compare sorption by the ion-exchanged forms of zeolite L with corresponding forms of erionite and offretite, in view of the structural similarities and differences among the three zeolites (3, 8) and the growing interest in erionite and offretite. Previous sorption... 

Apparent Saturation Capacities. For the ion-exchanged forms of zeolite L the apparent saturation capacities Nsat towards Ar at 77.3°K are in the sequence (Table III)... 

The oxidative dehydrogenation of cyclohexane to benzene has been studied more extensively. Transition metal ion-exchanged forms of zeolite Y have been shown (34-39) to be particularly active catalysts for this reaction. Although the platinum metal ions exhibit the highest activity, CuY was found to be the most selective for benzene formation (38, 39). 

Various ion-exchanged forms of zeolite Y have been investigated as catalysts for the oxidation of molecules such as y-butyrolactone (66), tetralin (67), aromatic amines (68), benzene (69), methanol (70), benzyl alcohol (71), and pyrocatechol (72). In general, transition metal ions or complexes have been incorporated into the zeolite. 

Desiccants. The ion-exchanged forms of zeolite A are well known as general laboratory and industrial drying agents in the form of extrudates or beads. The success of these... 

Figure 6. Cumene cracking on ion-exchanged forms of zeolite Y at 27rC and 0.43 W/hr/W...

TJirst studies (1, 2) of ion-exchanged forms of zeolite A reported that the exchange of Na for certain ions caused the breakdown of the zeolite lattice. However, Sherry and Walton (9) reported the existence of a hydrated BaA and concluded that the earlier reports of the nonexistence of this ion-exchanged form were based upon x-ray examination of calcined samples. Dyer, Gettins, and Molyneux (7) confirmed the existence of BaA and were able to measure Ba cation self-diffusion parameters in A. They also concluded that removal of water even at temperatures below 100 °C caused lattice collapse. Recently, Radovanov, Gacinovic, and Gal (8) have reported the preparation of Co(II)A in hydrated form, again contrary to the original studies. 

Kusnetsov, O. X, Activity and selectivity of ion exchange forms of zeolites NaX and catalysts NiO-AhOj-SiOj in propylene conversion, Neftekhimia, 20, 200, 1980 (Russian). 

The similarity in the adsorption behavior of krypton on the three kinds of mica surfaces suggests that the adsorption here is primarily due to dispersion forces, with very little contribution from ion-induced dipole forces. The results of Barrer and Stuart (1) for the adsorption of argon on various ion-exchanged forms of faujasite are similar. They found that while calcium, strontium, and lithium faujasite—i.e., the materials containing cations with greater polarizing power—did show heat effects correlatable with ion-induced dipole interactions, no such effects were observed with sodium, potassium, or barium zeolites. With the latter materials, they also concluded that the adsorbed argon possessed appreciable mobility. 

The sites adopted by cations in these structures are complex and will not be considered here but, broadly, an increase in Si/Al (decrease in framework charge) depopulates Sites I and T in the hydrated zeolites in favor of positions in the large cage. Removal of water causes an increase in population of the Sites I and T regardless of framework charge. Details of individual cation sitings in ion-exchanged forms of X and Y are available, with water molecule positions, where known. 

Clay minerals, natural and synthetic zeolites, silica and aluminum oxide forms generally are a mineral phase in mineral-carbon adsorbents. Natural aluminosilicates, particularly zeolites, due to the existence in their structure of ultramicropores and micropores (with pore diameter below 2 nm) with hydrophilic properties, exhibit high sorption capacity for particles of water vapor as well as sieve properties. They also demonstrate very good ion exchange properties. For instance, the ion exchange capacity of zeolite NaA is about 700 mval/100 g. 

The nature of the cations present in a zeolite can have a marked effect upon the rate of intracrystalline counterdiffusion, as shown by studies with several selected aromatic hydrocarbons in a series of ion-exchanged forms of the type Y zeolite. For 1-methylnaphthalene diffusing from type Y into bulk cumene, the desorptive diffusion coefficients vary by 2 orders of magnitude over different ion-exchanged forms in the order ... 

The main objective of this study was to determine the counterdiffusion characteristics of selected liquid hydrocarbons—benzene, cumene, 1-methylnaphthalene, and 2-ethylnaphthalene—in several ion-exchanged forms of the type Y zeolite and thus to begin to provide an understanding of the role which diffusion may be playing in various applications of zeolites. This is a part of the larger, theoretical problem of understanding the physics of molecular motion inside pores with diameters which approach the diameter of the molecules diffusing in them. 

Materials Used. The NaY zeolite and an ion-exchanged form of it, SK-500, were supplied by Union Carbide Corp., Linde Division, in the form of uncalcined powder. The SK-500 (Lot Number 12506-39) is a rare earth-ammonium exchanged type Y zeolite and had not been activated previously or calcined in its preparation. The calculated unit cell formula was... 

The protonic form of zeolite ZSM-5 Alj. Si,54 O,, Si/Al=35) obtained from MOBIL Corp. and a partially Rb ion exchanged form of X faujasite (Rb4 Naj4 Al Si,22 Oj, Si/Al=l. 75) obtained from Union Carbide Corp. were used as typical zeolites with an acidic and basic character, respectively. 

Beattie (6, 7) investigated the electrical conductivity of dehydrated analcites and chabazite. Freeman and Stamires (19) confirmed the conclusions of Barrer and Rees (4) and Beattie (6, 7) by electrical conductivity measurements at 200 Hz on various ion-exchanged forms of dehydrated synthetic zeolites of type A, X, and Y. They found a purely ionic conduction with a strong dependence of the activation energies on the nature of the zeolite and the kind of cation. The decrease of the activation energy in X and Y zeolites with increasing monovalent cationic... 

Again, this clearly points out possible limitations when rates of test reactions are compared for different zeolite types, especially when comparing large pore to small pore zeofites. Conversion of ethylbenzene over Na-, NH4-, Be-, Mg-, Ca-, Sr-, Ba-, and La-X and Y zeofites and H,K-L, NH4,K-L, Na-ZSM-5, and NH4,Na-ZSM-5 was studied in [158]. The Sr- and Ba-exchanged forms of Y and nearly all ion-exchanged forms of the X zeofites showed no or only a very low conversion. 

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.)... 

ESR and ESEM studies of Cu(II) in a series of alkali metal ion-exchanged Tl-X zeolites were able to demonstrate the influence of mixed co-cations on the coordination and location of Cu(II) (60). The presence of Tl(l) forces of Cu(II) into the -cage to form a hexaaqua species, whereas Na and K result in the formation of triaqua or monoaqua species. In NaTl-X zeolite, both species are present with the same intensity, indicating that both cations can influence the location and coordination geometry of Cu(II). The Cu(II) species observed after dehydration of Tl-rich NaTl-X and KT1-X zeolites was able to interact with ethanol and DMSO adsorbates but no such interaction was observed with CsTl-X zeolites. This interaction with polar adsorbates was interpreted in terms of migrations of the copper from the -cages. 

---