Silver exchange

The silver exchange of Na8[GaSi04]6(C104)2 sodalite, is carried out by taking appropriate amount of silver nitrate solution and sodalite. The IR frequencies observed for these sodalite derivatives in the region of 300-1200 cm 1, for successive Ag-exchange are shown in Table 1. 

Table 1 The IR frequencies of different samples of amount of silver exchanged in Na8[AlSi04]6(C104)2 sodalite derivatives.

The table 1 shows that the asymmetric stretching vibration, va linearly decreases with increasing amount of silver exchanged. This shift in IR frequency as a function of silver exchange is explained on the basis of cell constant. The silver halide sodalites have a... 

Some differences in arsenate and chromate adsorption on ODA-clinoptilolite and Pb-(Ag-linoptilolites) as well were recorded (Figs. 5 and 6). ODA-clinoptilolite exhibited more efficient arsenate and chromate removal from aqueous solutions than the inorganically exchanged modifications. However, silver exchanged clinoptilolite revealed higher capacity values for both oxyanions uptake than lead exchanged clinoptilolite did. This phenomenon supports preferred silver treated clinoptilolite utilization for specific water purification process even on the base of environmental acceptability. 

De Cremer G, Antoku Y, Roeffaers MBJ, Sliwa M, Van Noyen J, Smout S, Flofkens J, De Vos DE, Sels BF, Vosch T (2008) Photoactivation of silver-exchanged zeolite A. Angew Chem Int Ed 47 2813-2816... 

Although not exhaustive, the above summary of experiments with hydrogen chemisorbed on transition-metals serves to illustrate how neutron vibrational spectroscopy is performed with catalytic substrates and the methods used to analyze the inelastic neutron spectra. In concluding this section we note that the technique can be extended to supported catalysts such as in recent experiments with hydrogen adsorbed on both MoS and alumina supported MoSp (38). Also, as another indication of the variety of systems which can be studied, we note earlier experiments with ethylene (39) and acetylene (40) adsorbed on silver exchanged 13X zeolites. "Tn this work, deuteration of the molecules was helpful in identifying the surface vibratory modes on these ionic substrates of greater complexity. 

In the case of cyclic or cr-substituted tin enolates 358, it was found that E-enolates provide //-products 359, whereas the corresponding Z-tin enolates give syn-aldols (Scheme 105).315 Thus, the reaction seems to follow the classical Zimmerman-Traxler transition states 360/361 whereby the chiral silver catalyst activates the aldehyde. A possible alternative is a tin-silver exchange and formation of an analogous transition state of the silver enolate. 

Zeolites are attractive host materials as they present regular channel systems, providing crystallographic defined locations for metal clusters. Hence, the size of the clusters inside the zeolites can be limited by the dimensions of their channels and cages. Zeolite-supported noble metal catalysts were extensively studied due to their wide application as catalysts in petroleum industry.Reduction of silver in zeolite hosts has been carried out by /-irradiation.The intermediate paramagnetic (charged) silver clusters formed in /-irradiated silver-exchanged zeolites have been studied by electron spin resonance (ESR)... 

Silver-exchanged zeolite Asymmetric HR, alkenyl iodides Increased ee [121b]... 

In comparison with the dehydrated AgX the shifts for the oxidized form of AgX are lower by about 10 ppm. In our opinion, the unusual 129xe NMR chemical shifts of the silver-exchanged X zeolite are due to a specific interaction of xenon with the silver cations in the supercages, especially silver cations in Sill... 

Ag solid-state NMR data were used to probe dynamics and local environment of silver cations in a series of silver-exchanged zeolites.606 Solid-state 2H NMR spectra gave evidence on the structure and dynamics in the clathrates Gd(L)2Ni(CN)4.2C4H4NH, where L = NH3, l/2en C4H4NH = pyrrole.607... 

In 1962, Ralek et al. reported that after dehydration-rehydration treatment, the silver-exchanged zeolite A changed from white (hydrated) to yellow to orange and finally to brick-red in color.1241 In 1977, Kim and Seff observed a similar phenomenon for Ag-A single crystal when it was treated carefully at 400 °C, and they revealed that after dehydration there exist Ag6° metal clusters in the Ag-A zeolite on the basis of XRD analysis (Figure 9.8).[25] Later, Jacobs et al. revealed that Ag32+ clusters may be present in the zeolite.[261... 

The major products were -( ) and y- (II) picolines traces of pyridine and small amounts of ethylpyridines and higher molecular weight bases were also formed. Similar products have been observed when the same reactants were passed over silica-alumina 148). Zeolite catalysts, notably silver-exchanged X-type faujasites, have also proven effective in the synthesis of methylpyridines from acetylene and NHs, and methylacetylene and NHs, at temperatures ranging from 100° to 300° 149). 

Metal atom clusters in the 26-hedra could (as with water molecules) contain many metal atoms. An example is the fourteen atom Agg+8Ag+ cluster in Y-irradiated zeolite Ag-A[25]. Saturation is achieved for mercury sorbed into silver-exchanged faujasites and other zeolites [26]. The Ag+ is reduced to Ag atoms and then at an approximate critical pressure of mercury vapour there is nucleation of mercury clusters which fill all the pore volume as the pressure of Hg vapour increases further. Mercury-zeolite systems are the oily ones in which sorption isotherms have been investigated quantitatively. Hcwever other metal atoms introduced into zeolites (by ion exchange and reduction, or as metal carbonyls and their decomposition) all show, on heating, a strong tendency to form clusters by migration of atoms, which can aggregate both within and outside the crystals. 

Keywords hydroamination, alkyne, silver-exchanged tungstophosphoric acid... 

Further examples of acoustic sensors modified with zeolites include a QCM sensor with silver-exchanged ZSM-5 that responds selectively to acetone (in diabetic s breath) in the ppm-range,ll 16] principal component analysis of multiple QCM-sensor responses (with LTA, MFI, SOD) for the detection of NO/SO2 mixtures,[117] MFI-zeolite-coated microcantilevers with ppm-sensitivity for Freon detection [118,119] and other zeolite-coated cantilevers for humidity sensing.[120]... 

Tam C N, Trouw F R and Iton L E (2004), Inelastic neutron scattering study of the activation of molecular hydrogen in silver-exchanged A zeolite first step in the reduction to metallic silver at low temperature , JPhys ChemA, 108, 4737. 

Acetylene adsorption was IR spectroscopically studied by Howard and Kadir [833], who dealt with the uptake of this unsaturated compound into silver-exchanged zeoHte A. They could evidence the formation of acetylides and the formation of two different adsorption complexes of n-bonded acetylene, indicated by bands at 1955 and 1912 cm for CjHj and 1740 and 1710 cm for CjDj imder an adsorbate pressure of 13.3 kPa. 

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