Metal cation exchange

Di or trivalent cations are able to induce the dissociation of coordinated water molecules to produce acidic species such as MOH+ (or MOH2+ for trivalent metal cations) and H+. Several infrared studies concerning rare-earth or alkali-earth metal cation exchanged Y zeolites have demonstrated the existence of such species (MOH+ or MOH2+) [3, 4, 5, 6]. However, the literature is relatively poor concerning the IR characterization of these acidic sites for LTA zeolites. The aim of the present work is to characterize 5A zeolite acidity by different techniques and adsorption tests carried on 5A zeolite samples with different ion exchange. 

Thermodynamic data for alkali metal cation exchange at 25 °C (in kJ equiv ) Camp Berteau and Wyoming Bentonite... 

Even if the metal cation exchanged zeolite is not dehydrated, the introduction of the ligand or its precursors frequently requires thermal treatment, which can redistribute the cations within the zeolite. Not all metal ions will become com-plexed and their presence can complicate the characterization of the materials as well as the interpretations of catalytic reactions. In principle, the uncomplexed metal ions should be removed by back-extraction. Unfortunately, however, this is a requirement more frequently honored in the breach, rather than the observance. 

Cast, R. G., "Alkali Metal Cation Exchange on Chambers Montmorillonite," Soil Sci. Soc. Amer. Proc., (1972), 36, 14. 

As it was shown in the case of pentasil zeolites (MOR, FER, MFI), UV-VIS-NIR DR spectroscopy and UV-VIS emission spectroscopy appear to be extremely powerfiill tools for the characterization of transition metal ions in molecular sieve matrices [1,5]. The aim of this study is to employ this promissing and powerfull technique for the characterization of siting of metal cations exchanged into the (A1)MCM-41 matrix. 

The topic of catalysis with Nafion has recently been reviewed in detail (56). Apart from using Nafion-H primarily as a solid superacid catalyst, a number of reports have described the use of functionalized Nafion derivatives by metal cation exchange to achieve various types of organic reaction. These include a bifunctional catalyst (acid and cation site), a heterogeneous perfluorosulfonate salt (only cation sites), and a trifunctional... 

Gast, R. G. 1972. Alkali metal cation exchange on Chambers montmorillonite. Soil Sci. Soc. Am. Proc. 36 14-19. 

Sposito, G. and S. V. Mattigod. 1979b. Ideal behavior in Na-trace metal cation exchange on Camp Berteau montmorillonite. Clays Clay Mineral 27 125-128. 

Hunger B., Klepel O., Kirschhock C., Heuchel M., Toufar H. and Fuess H., Interaction of water with alkali-metal cation-exchanged X type zeolites TPD and XRD study. Langmur, 15 (1999) pp. 5937-5941... 

Typical results for the benzylation of 1-decanol in hexane are shown in Table I. Although an insoluble base such as K2CO3 was ineffective for the reaction, alkali metal cation-exchanged Y-type zeolites efficiently induced the reaction, and the highest yield (73%) was obtained when KY was used. The... 

Metals Cation-exchange stepwise elut. Silicates AAS ppm-Range 152)... 

If selectivity were governed solely by interactions of a purely electrostatic (coulombic) nature one could anticipate negative enthalpies and entropies of exchange due to dominant contributions by A and A5ii respectively. This is indeed found for alkali metal cation exchange on styrenic sulfonate resins as illustrated by Table 5.3a. 

Methanol Decomposition over Metal Cation-Exchanged Faujasitese... 

Cation-exchange chromatography in acetone-HCl [7], or acetone-HBr [8] media has been employed for separation of copper from many other metals. Cation-exchangers have also been used for preconcentration and separation of trace amounts of copper [9,10]. 

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