Ion exchange in zeolites

The behavior of transition metal ions exchanged in zeolites is very similar to that in a homogeneous medium CuPdY zeolites are efficient substitutes for Wacker chemistry in absence of chloride ions. 

A large body of information has been published on polyvalent ion exchange in zeolites. Examples of alkaline earth ion exchange in zeolites include studies on ion exchange of Na-A (5),... 

Sherry, in the last few years, has been generalizing all knowledge about selectivity during ion exchange in zeolites this author has summarized the selectivity rules as follows [21] every zeolite has preference for Na+ instead of Li+ and NH4 instead of Na+ zeolites with a low Si/Al ratio have preference for Ca2+ and zeolites with a high Si/Al ratio have preference for alkaline cations zeolites are selective for polarizable cations and the electroselectivity, molecular sieving, and space limitations rules are valid. 

CHEMICAL AND POLLUTION ABATEMENT APPLICATIONS OF ION EXCHANGE IN ZEOLITES... 

For designing a canister system for heavy metal removal (see Figure 7.12) [38,53], a simple phenomenological description of dynamic ion exchange in zeolite bed reactors was worked out, which allows for the design of modular canister ion-exchange bed reactors for applications in heavy metal removal from wastewater. 

Another example is the synthesis of supported oxide catalysts by spreading of one oxide across the surface of another (support) oxide in physical mixtures. Also, the phenomenon of solid-state ion exchange in zeolites may be discussed within the framework of the wetting and spreading concept. 

Calorimeter. A differential calorimeter, operating at 25.0 °C under near-isothermal conditions, was used for all heat measurements. Similar calorimeters, designed for determining heats of ion exchange in zeolites, have been described previously (5, 6, 14, 15). The calorimeter was calibrated by measuring the heat of solution of potassium chloride in water. The ratio of the area under the curve traced by the recorder pen to the heat produced was 1.50 dz 0.04 cm per calorie. No heat could be detected when an empty evacuated bulb was broken under water. 

T. Sprang, A. Seidel, M. Wark, F. Rittnera, and B. Boddenbe, Cadmium Ion Exchange in Zeolite Y by Chemical Vapour Deposition and Reaction. J. Mater. Chem., 1997, 7, 1429-1432. 

Figure 6. La-Na ion exchange in zeolite X at 25°C as a function of total normality...

Alkaline Earth Ion Exchange of Zeolites X and Y. In recent years, alkaline earth ion exchange in zeolites X and Y has been studied thoroughly. In 1966, Barrer, Rees, and Shamsuzzoha reported on alkaline earth ion exchange in zeolite X at 25°C (12), and in 1968, Barrer, Davies, and Rees reported on exchange in zeolite Y at 25°C (6). In 1968, Sherry reported on alkaline earth ion exchange in zeolites X and Y over the temperature range of 5° to 50°C (54). 

Ammonium and Alkyl Substituted Ammonium Ion Exchange in Zeolites X and Y. In 1968, Theng, Vansant, and Uytterhoeven reported (60) on their study of the exchange of ammonium ions and alkylam-monium ions in zeolites X and Y. They found that, in general, not all of the Na+ ions could be replaced. They agreed with an earlier report (54) that 16 Na+ ions per unit cell of NaY could not be replaced by... 

Karge, H.G., 1992, Modification of zeolites and new routes to ion exchange, in Zeolite Microporous Solids Synthesis, Structure, and Reactivity, eds E.G. Derouane, F. Lemos, G. Naccache and F.T. Ribeiro, Vol. C-352 of NATO ASI Series (Kluwer Academic Publishers, Dordrecht) pp. 273-290. 

Karge, H.G., G. Borbely, H.K. Beyer and G. Onyestyak, 1988a, Solid-state ion exchange in zeolites. Part HI. Preparation and test of lanthanum zeolite catalysts, in Proc. 9th Int. Congress on Catalysis, Ottawa, 1988, eds M.J. Phylips and M. Teman (The Chemical Institute of Canada, Ontario) pp. 396-403. 

Townsend, R.P, 1986, Ion exchange in zeolites Some recent developments in theory and practice, in New Developments in Zeolite Science and Technology, eds A. Ijima and J.W. Ward, Vol. 28 of Studies in Surface Science and Catalysis (Elsevier, Amsterdam) pp. 273-282. 

Townsend, R.P., 1991, Ion exchange in zeolites, in Introduction to Zeolite Science and Practice, eds... 

In the development of zeolite science, infrared spectroscopy has been one of the major tools for structure and reactivity characterization. However, the field of zeolite Raman spectroscopy is gaining importance. The Raman effect is an intrinsically weak phenomenon, and Raman spectra of zeolites are often obscured by a broad fluorescence. Just like IR spectroscopy, Raman can detect small. X-ray amorphous zeolite particles. Therefore, Raman spectroscopy has been used to examine zeolite synthesis mixtures with ex-situ methods (with separation of solid and liquid) and in-situ methods. In this work we give an overview of the zeolite framework vibrations, zeolite synthesis, adsorption on zeolites and metal substitution and ion exchange in zeolites. 

A great deal is known about ion exchange in zeolites, because of their importance as detergent builders - Zeolite A is the most widely used. Most of the cation sites in zeolite A are accessible in or from the large a-cages (Figure 6.7)... 

ABSTRACT. Early observations and more recent systematic studies of solid-state ion exchange in zeolites, which is a possible way of zeolite mo fication, are reviewed. Particular attention is paid to the presentation of important experimental techniques which are appropriate to prove solid-state reaction in zeolites and determine the degree of such solid-state ion exchange. Examples are provided for the introduction of alkaline, alkaline earth, rare earth and transition metal cations into zeolites such as A, X, Y, mordenite and ZSM-5. Techniques of investigation are IR, ESR, MAS NMR, XRD, XPS, TPD and chemical analysis. 

Zeolites are ion exchangers. Very early on, their ion exchange properties attracted the attention of scientists both for basic and applied research. A large body of pertinent literature on ion exchange in zeolites exists, and the field was reviewed several times [6-8]. A very recent excellent article on ion exchange in zeolites was contributed by Townsend [9] as a chapter of the book Introduction to Zeolite Science and Practice . 

The studies on ion exchange in zeolites almost exclusively concerned the conventional ion exchange. Briefly, this is carried out by suspending crystallites of a zeolite with cation A in a salt solution of the cation B which is supposed to go into the zeolite structure and there replace cation A. However, there were some early observations that ion exchange with zeolites might occur in solid-state as well [10-14]. Thus, Rabo et al. [10-12] described, in their work on salt occlusion in zeolites, the replacement of protons by sodium cations. They calcined a mixture of NaCl and Na-Y which contained residual acidic OH groups. 

Solid-state reactions between halides and hydrogen forms of zeolites were also observed by Clearfield et al. [13] using ESR spectroscopy. For a long time, there was essentially no further activity in the field of solid-state ion exchange in zeolites. However, such studies were resumed more recently by several research groups. 

Lazar, K. Pal-Borbely, G. Beyer, H. K. and Karge, H. G., Solid-state ion exchange in zeolites. Part 5. NH4-Y-iron(II) chloride. Journal of the Chemical Society, Faraday Transactions 90(9), 1329-1334 (1994). 

Figure 6.28. Temperature-programmed mass spectrometry of the decomposition of Pt +(NHs)4 ion exchanged in zeolite nZEM-Sl " . The corresponding reaction steps are indicated. Three peaks can be distinguished in the TPD spectrum. Oxygen is consumed in only two of the N2 formation peaks. The mechanism that explains the occurrence of these three peaks is consistent with proposals made earlier on the homogeneous oxidation of Ru-amine complexes in basic solutionl and the reaction of NO with Ru or Os complexes ].

---