Influence of exchangeable cations

The Influence of Exchangeable Cations on Zeolite Framework Vibrations... 

The influence of exchangeable cations on zeolite framework vibrations was investigated by Maxwell and Baks [285], and, similar to the studies of Flanigen et al. [112], they derived linear relationships between the reciprocal of the sum of the cation radii and oxygen anion radius, l/frcation+fo -) and the wavenumbers of framework vibrations of zeoHtes A and X. 

I. Shainberg and H. Otoh, Size and shape of montmorillonite particles saturated with Na/Ca ions (inferred from viscosity and optical measurements), Israel]. Chem. 6 251 (1968). L. L. Schramm and J.C.T. Kwak, Influence of exchangeable cation composition on the size and shape of montmorillonite particles in dilute suspension, Clays and Clay Minerals 30 40 (1982). 

Zeolites are known to be important catalysts for a number of industrially important reactions. A question of basic interest, which provides opportunity for development of catalyst with suitable and tailored characteristics, is to determine the correlation between number, strength and strength distribution of active sites and the promotion of catalytic activity. Therefore, the investigation of acid sites, both Lewis and Bron-sted type, is very important subject. Properties of zeolites as catalysts will depend on many factors the adsorption or desorption temperature of the probe, pretreatment of the sample, proton exchange level, influence of coking as well as Si/Al ratio and dealumination and influence of exchanged cations [47]. 

Kieger, S., Delahay, G. and Coq, B. (2000) Influence of co-cations in the selective catalytic reduction of NO by NH3 over copper exchanged faujasite zeolites, Appl. Catal. B 25, 1. 

The influence of exchangeable monovalent cations on the framework vibrations for the hydrated zeolites Linde A and X has been investigated. An approximately linear relationship is found between the frequency of some absorption bands and the inverse of the sum of the cation and framework oxygen ionic radii. It is proposed that the shift in framework vibrations is largely caused by those cations which are strongly interacting with the zeolite framework. Thus the linear relationship indicates that these monovalent cations are all similarly sited in the zeolite lattice. This is consistent with the presently available x-ray analyses on some of these zeolites. Since Rb + and Cs + are only partially exchangeable in both Linde A and Linde X, these cations deviate from this linear relationship. 

The activity of clay minerals, proven in the reactivity of terrestrial (15-16), and postulated in Martian (j ) soils, is disproportionate to their quantity, relative to other minerals. This is the result of several factors small particle size, high specific surface area, Bronsted and Lewis acidity, redox and other potentially catalytically active sites common to clay minerals, and a limited capacity for size exclusion (which is influenced by the number and valence of exchangeable cations ( )). 

The most powerful methods for the study of adsorption mechanism of nitroaromatic compounds on clay minerals have become in situ spectroscopic investigations. Handerlein et al. [152, 153] and Weissmahr et al. [154-156] have investigated the adsorption of NACs particularly on illites, montmorillonites and homoionic kaolinites. The substituted nitrobenzenes on the surface of smectites were investigated by Boyd et al. [157, 158], The main focus in the experimental study of adsorption of NACs on the surface of clay minerals is the influence of the type of clay mineral, the effect of exchangeable cation of the mineral, the effect of the structure and the kind of substituents of NAC compound on the position and orientation of NACs to the surface of mineral, the character of interaction between NACs and the surface of mineral, the adsorption energy. 

The rapid separations of carbohydrates by means of zone electrophoresis may be of value in studying the course of a reaction. Thus, Stacey and coworkers were able to follow the conversion of D-glucal and of D-galactal into 2-deoxy-D- glucose and 2-deoxy-n- galactose, respectively, under the influence of a cation-exchange resin (H form). The reaction was shown to be quite complex. 

Montmorillonites are more frequently used as Bronsted acid catalysts even if Lewis acidity plays a role in their catalytic activity. The origin of Bronsted acidity in metal-exchanged montmorillonites is ascribed to the polarizing influence of the cation on the water molecules in spatially restricted interlayers. The exchangeable cations are either protons or polarizing cations [e.g., aluminum, chromium(III), or iron(III)]. 

The diffusion properties of zeoUtes may be significantly influenced by their content of exchangeable cations. As an example, by both nuclear magnetic relaxation [1,143] and PEG NMR [145] measurements, the molecular mobility of aromatics in zeolite Na-X was found to be larger than in Na-Y. Since the adsorbate-adsorbent interaction of unsaturated hydrocarbons is dominated by the interaction between the n electrons of the double bonds and... 

DRIFT studies of the clinoptilolite framework were carried out by Ehzalde-Gonzales et al. [258], who observed bands at 1633,1417,1018 cm" (Vas[T-0-T]) and a shoulder at 1200 cm (assigned to inter-tetrahedral vibrations). The influence of the treatment temperature and the Sanderson electronegativity of exchange cations (Na+, K+, Mg, Ca ) on the framework vibrations of natural chnoptilohte was studied by Rodriguez-Fuentes et al. [259] and interpreted in close analogy to the FKS correlation [112,114]. 

Under the influence of water, cationic manganese compounds decompose immediately, as in organic donor solvents such as acetone and tetrahydrofuran. In contrast to isoelectronic compounds of the chromium group, diolefin technetium and rhenium complexes have cis structures. In aqueous solution, the cation [Re(CO)4 ( 2114)2] is stable the Re —C2H4 bond in [Re(CO)5 ( 2114)] is also stable. There is no exchange between free ethylene and the ethylene in the complex. 

The composition of exchange cations manifests its effect on the structure formation of clay sediments by changing the forces of repulsion between particles as a result of the ion-electrostatic interaction and the wedging-out action of adsorbed bound-water films. In the first case, this is caused by the varying capacity of cations to dissociate from particle surfaces and form diffuse layers of different thickness, and in the second, by the influence of cations on the specific hydrophility of clay minerals. 

In order to study the influence of the amount of exchanged cations on the gas adsorption properties of the porous substrate, two different PILCs have been prepared with a different Ca loading. The N2/O2 ratios of the Ca -Al-PILCs at 273 K are determined as a function of the pressure (Fig. 15). Both PILCs have a higher preference for nitrogen than the parent Al-PILC (N2/O2 = 1), and the PILC with the highest cation amount (2.23 wt%) exhibits a better N2/O2 selectivity. Compared to the Sr +-exchanged PILCs, the capacities obtained on the Ca -Al-PILCs are higher (88). 

Thomas, B. Sugunan, S. Influence of residual cations (Na, and Mg ) in the alkylation activity of benzene with 1-octene over rare earth metal ion exchanged FAU-Y zeolite. Mzcro/)or. Mesopor. Mater. 2004, 72, 221-23%. 

The mechanism for the polymerisation of acetylene is inherently different from that of aromatic monomers such as pyrrole or thiophene. Whereas the polymerisation of pyrrole or thiophene involves a redox reaction,(77,74) the corresponding reaction of acetylene is probably initiated by acidic properties of the catalyst.(22) In the case of polyacetylene evidence has been obtained to suggest that the nature of the cations in the zeolite lattice is also important.(75) Fig. 1 shows a series of Raman spectra which illustrate the influence of various cations upon the extent of polymerisation, demonstrate the effect of elevating the acetylene pressure and indicate a role for Lewis acid sites in the reaction mechanism. Exposure of acetylene (0.1 MPa) to sodium-mordenite (NaM) at 295 K gave the spectrum displayed in Fig. 1(a). Bands at 398 and 468 cm are ascribed to lattice modes of the mordenite structure(2J), whereas the peak at ca. 1958 cm can be attributed to the Vj vibration of adsorbed monomeric acetylene bound in a side-on" manner to cation sites (16,23). Relatively small maxima at 1112 and 1502 cm are characteristic of trans-polyacetylene (5,18,24,25). Exchange of cesium for the sodium ions in mordenite was found to be beneficial for the formation of polyacetylene, as can be seen in Fig. 1 (b). In addition to the noted intensification of bands typical of rra/iy-polyacetylene at 1112 and... 

C.G. Arges, J. Parrondo, G. Johnson, A. Nadhan, V. Ramani, Assessing the influence of different cation chemistries on ionic conductivity and alkaline stability of anion exchange membranes, J. Mater. Chem., 22 (2012) 3733-3744. 

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