Crystal destruction of zeolite NaA during ion exchange with magnesium and calcium ions (original) (raw)
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An investigation of ion exchange in Linde A has been completed. The preliminary work involved characterizing the lot of Linde 4-A used and establishing the equilibrium conditions. Ion-exchange isotherms for the T1+ and Ag+ exchange for Na+ demonstrate that an average of 0.36 NaAlOz is occluded in each sodalite cage in the crystal. It is shown that a perfectly crystalline hydrated Ba-A can be prepared from Na-A. The maximum in plots of selectivity coefficient vs. per cent loading of alkaline earths, reported for the Ca-Ea-A system by other investigators, has been found to be a result of not reaching equilibrium a t low loadings. When equilibrium was reached a t all loadings, the selectivity coefficient continuously decreased with increasing per cent loading of Ca2 +, Sr2+, and
The Journal of Physical Chemistry B, 2000
The structure of a single crystal of fully dehydrated K + -exchanged zeolite X was determined by X-ray diffraction methods in the cubic space group Fd3 hm at 21°C; a o ) 25.083(5) Å. Ion-exchange of a crystal of Na 92 Si 100 -Al 92 O 384 was done at 80°C using flowing aqueous 0.1 M KNO 3 with pH ) 12; 90(3) K + ions were found per unit cell. R 1 ) 0.066 for 352 reflections for which F o > 4 σ(F o ); wR 2 based on F 2 and all data is 0.193. The structure of dehydrated K-X is much more complex than that of dehydrated Na-X; K + ions are found at nine crystallographic sites, a large number due to cation crowding. Two distinct site I and three site I′ positions are occupied by six, eight, four, four, and four K + ions per unit cell, respectively. Ten of the 16 double six-rings each accommodate two K + ions with short K + ‚‚‚K + distances of 3.79(4) and 3.92(8) Å, indicative of the degree of cation crowding. Site II is nearly fully occupied with 28.4(4) K + ions. The remaining 36 K + ions are found at one III and two III′ sites; these appear to be close in energy for K + ions so that no single site is preferred.
Failure of ion exchange into zeolites A and X from four diverse nonaqueous solvents
Zeolites, 1995
Fully anhydrous ion exchange into zeolite single crystals was attempted using nonaqueous solutions. Under various conditions, Na-A was exposed to flowing solutions of CuCI, CuCI2, and CuSO4 in acetonitrile and of CuCI 2 in methanol. Na-A was treated with dimethyl sulfoxide solutions of Pb(NO3) 2 and, at 140°C, KNO 3. Finally, Na-A and Na-X were treated with HgS in liquid sulfur at 400°C. X-ray crystallography showed that in no case had any ion exchange occurred. Perhaps cations neither enter the zeolite nor leave sites within because their solvation complexes cannot hydrogen bond to framework oxygens.
Electrochemically Controlled Ion Exchange: Proton Exchange with Sodium Zeolite Y
Angewandte Chemie International Edition, 2005
Structural characterisation of proton-exchanged zeolites, prepared using ion-transfer at the liquid-liquid interface, is reported. Specifically, electrochemical exchange of protons for sodium with zeolites X and A is described: the structural integrity of the resultant materials was probed by solid-state NMR spectroscopy and temperature-dependent powder X-ray diffraction. It is shown that replacement of ca. 40 % of the Na + can be achieved using this approach for both zeolites; however, the results indicate that exchange is accompanied by significant structural degradation in the case of zeolite A, with proton exchange occurring at the amorphous regions of the sample. In contrast, zeolite X retains its structure, and the level of proton exchange is comparable with the highest levels reported using conventional chemical methods, highlighting the utility of the electrochemical approach.
Thermal crystallization of ion-exchanged zeolite A
Journal of The European Ceramic Society, 2003
The zeolite 4A (Na 12 Al 12 Si 12 O 48 . 27H 2 O) was subjected to cationic exchange with an aqueous solution of Li + 0.5 M at 70 C. After three exchanges for 24 h, about 100% of Na + was removed obtaining the Li-exchanged form (Li)-A. Despite this quite complete exchange, some undesired and occluded NaAlO 2 was detected in the typical structural cages of precursor. The partial exchange of Li with equivalent amounts of Ca or Mg, allowed the formation of (Li-Ca)-or (Li-Mg)-exchanged zeolitic forms characterized by different Ca or Mg contents, respectively. These various zeolitic precursors have been thermally treated at increasing temperatures up to 1170 C. The transformations into other crystalline phases occur immediately after the formation of intermediate amorphous phases originating from the thermal collapse of zeolitic precursors. From the (Li)-A zeolite-based precursor, a small amount of nepheline (NaAlSiO 4 ) and b-eucryptite (LiAlSiO 4 ) crystallize, while during the thermal transformation of Li-Ca-containing precursors, anorthite [(Ca,Na)Al 2 Si 2 O 8 ] and b-eucryptite-like phase are formed. Stuffed derivatives of quartz relatively richer in SiO 2 crystallize from (Li-Mg)-containing precursors. The Mg content of the zeolitic precursor affects the type of secondary crystallized phases and consequently the composition of the corresponding stuffed derivative of quartz. #
Obtaining of the Mg2+ form of the zeolite 4A with ion exchange of magnesium salts
Journal of Process Management. New Technologies, 2016
Zeolites are sodium alumino silicates which in in their composition contain zeolite water. They have a three-dimensional structure. Spatial structure defined by a strictly defined geometry of pores and cavities. For ionic еchange is used magnesium salt (MgCl 2 *6H 2 O) whose aqueous solutions were with the following concentrations (MgCl 2 *6H 2 O) = 2,5; 3.5; 4,5 mol / dm 3 , and other parameters of the ion exchange: time t = 20, 30, 40 and temperature of 298 and 330 K. Ionian capacity is calculated as mmgMgO / 1g zeolite.
On the Lewis acidity of protonic zeolites
Applied Catalysis A: General, 2015
IR spectra of hydroxyl groups, adsorbed CO, pivalonitrile and pyridine on three H-MFI zeolite samples and on two H-Y faujasites are reported and discussed. Samples richer in Al (H-MFI (Si/Al2 = 30) and H-Y (Si/Al2 = 5.1)) show the presence of extraframework species and the presence of Lewis acidity together with Brønsted acidity. H-MFI with lowest Al content (Si/Al2 = 280) does not show any extraframework species (EF) and only presents Brønsted acidity. H-MFI with intermediate Al content (Si/Al2 = 50) possess very small amount of EF species and of Lewis acidity. H-Y with low Al content (Si/Al2 = 30) does not show extraframework species but shows the presence of Lewis acidity together with Brønsted acidity. The role of extraframework material as carrier of Lewis acidity is confirmed. It is proposed that Lewis acidity of low Al-content H-Y can arise from framework tetrahedral Al ions, which can enlarge their coordination to five without any previous dehydroxylation. A support for this hypothesis is given by the reversible shift of the LF OH stretching band, whose extent depends on the strength of the basic molecules: this is certainly not due to a direct interaction of the OH groups responsible for the LF band, which are located in cavities (sodalite cavity and hexagonal prisms) where the molecular probes cannot access.
The Exchange Mechanism of Alkaline and Alkaline-Earth Ions in Zeolite N
Molecules
Zeolite N is a synthetic zeolite of the EDI framework family from the more than 200 known zeolite types. Previous experimental laboratory and field data show that zeolite N has a high capacity for exchange of ions. Computational modelling and simulation techniques are effective tools that help explain the atomic-scale behaviour of zeolites under different processing conditions and allow comparison with experiment. In this study, the ion exchange behaviour of synthetic zeolite N in an aqueous environment is investigated by molecular dynamics simulations. The exchange mechanism of K+ extra-framework cations with alkaline and alkaline-earth cations NH4+, Li+, Na+, Rb+, Cs+, Mg2+ and Ca2+ is explored in different crystallographic directions inside the zeolite N structure. Moreover, the effect of different framework partial charges on MD simulation results obtained from different DFT calculations are examined. The results show that the diffusion and exchange of cations in zeolite N are a...
Dark field TEM and X.P.S. of proton exchanged erionite—offretite (T) zeolites
Zeolites, 1985
reduced the AI content on the surface of the H-Y zeolite to half of the bulk value. External layers of dealuminated zeolites remained rich in aluminium though some decrease in the A1/Si (surface) value was observed ( ). The sorption capacity of the H-Y zeolite decreased to 88% of the initial value, but this effect was not found with dealuminated zeolites. Thus, only a slight amorphization of the H-Y zeolite could take place; considerable structural collapse did not occur. It has been reported 8 that, at 790 K, the framework OH groups of the H-Y zeolite undergo dehydroxylation while hydroxyls of the dealuminated Y zeolites are thermally stable. This dehydroxylation together with subsequent readsorption of water at room temperature had marked influence on the acidic properties of the H-Y zeolite in comparison with the original H-Y: the number of OH groups substantially decreased and new electron-accepting sites attributed to A1 atoms appeared. Again, no such pronounced acidity changes were found in dealuminated zeolites. (Acidity was determined with pyridine) 8. This comparison implies, that the change in the surface composition resulting from the dehydration-rehydration cycle, i.e. the decrease of A1 content, is connected above all with the changes of the zeolite structure caused by the dehydroxylation at high temperature and following hydrolysis at room temperature. In this treatment the dealuminated Y zeolites are considerably more stable than H-Y zeolites. It should be noted, that zeolites without framework hydroxyls (for instance Na forms) behave quite differently. According to the literature 2 only small changes of Si/A1 ratio occur with Na-Y and Na-M zeolites even after their thermal collapse at 1170 K.
ION EXCHANGE PROPERTIES OF GEORGIAN NATURAL ZEOLITES
Ion exchange properties of Georgian analcime, phillipsite and scolecite have been studied. The exchange capacity of analcimes is higher for sodium cations, decreasing in the following series: Na + >K + >Ag + >NH 4 + >Ca +2 >Sr +2 >Li + , the selectivity sequence for the sodium-enriched form is NH 4 + >Ag + >Li + >Ca +2 >K + ~Sr +2. For phillipsite ion exchange isotherms prove the high selectivity towards NH 4 + and K + depending on the origin of zeolite: K + >NH 4 + >>Ca +2 >Mg +2 for samples with comparatively low content of potassium, and NH 4 + >K + >Na + >>Ca +2 >Mg +2 for samples with high K-content. For scolecite selectivity sequences depend on temperature and flow rate, at low temperatures and under static conditions the selectivity sequence is Sr +2 >Ba +2 >Rb + >Ca +2 >Cs + >K + >NH 4 + >Na + >Mg +2 >Li + >Cd +2 >Cu +2 >Mn +2 >Zn +2 >Co +2 >Ni +2 .