Synthetic Faujasites Research Articles

Sorption of Lead(II) from Aqueous Solutions by Synthetic Zeolites

A comparative study of the sorption of lead(II) from dilute aqueous solutions by synthetic faujasites, chabazites, mordenites, erionites, phillipsites, and type A zeolites was performed. The most promising sorbents are low-silica chabazites and potassium erionites with relatively high SiO2/Al2O3 ratio.

Zeolites for nuclear waste treatment: Co, Ni, Zn uptake into synthetic faujasites X & Y

Synthetic zeolites X & Y have been examined for their abilities to take in Co, Ni and Zn radioisotopes. Distribution coefficients (Kd) have been determined, with and without competing cations, and at various pH values. Elution studies on zeolites containing Co, Ni and Zn radioisotopes considered the effect of acid and alkaline conditions, calcination and cement encapsulation. Leach rates arising from these experiments have been calculated. The general conclusions can be drawn are that zeolites X & Y are suitable for decontamination of aqueous wastes containing Co, Ni and Zn. Cement encapsulation is appropriate but no advantage accrues from pre-calcination. Some comments on the likely mechanism of leaching losses have been made.

Study of Si and Al ordering in the framework of siliceous cubic and hexagonal faujasite zeolites

Cubic faujasites of Si/Al = 1.7 to 3.7 and hexagonal faujasites of Si/Al = 3.3 and 4.0 were synthesized hydrothermally and were compared with secondary synthetic faujasites of Si/Al = 2.7 to 7.9 derived from SiCl 4 or (NH 4) 2SiF 6 treatment. XRD, IR and solid-state NMR ( 29Si, 27Al and 23Na) were used to characterize the materials. Both the unit cell size, a 0 and the framework vibration frequencies of faujasites obey a linear relationship with the content of framework aluminum as determined by 29Si MAS NMR. Comparisons of experimental 29Si NMR with the theoretical models of Si and Al ordering suggest that the β-cage model can be applied to fit the aluminum distribution in directly synthesized cubic and hexagonal faujasites, while the aluminum distribution in the framework of the (NH 4) 2SiF 6-treated samples, CSY, is based on the random siting model with Loewenstein's rule.

Calorimetric study of NH 3 and CO 2 adsorption on synthetic faujasites with Ca 2+, Mg 2+, and La 3+ cations

The heats of CO 2 and NH 3 adsorption on sodium, calcium, magnesium-calcium, and lanthanum-calcium forms of synthetic faujasites were studied. The Ca 2−, Mg 2+, and La 3+ cations in zeolites are preferential adsorption centers for NH 3. The substitution of Na + by Ca 2+ in zeolites leads to an increase of CO 2 adsorption heats at low coverages. With the introduction of Mg 2+ and La 3+ in calcium faujasites the heats of CO 2 adsorption decrease sharply. This suggests that most of the ions in magnesium-calcium and lanthanum-calcium zeolites do not interact directly with adsorbed molecules. All measurements of adsorption heats were made using Calvet microcalorimeters at 308 K (NH 3) and 303 K (CO 2).

Application of deconvolution to the analysis of univalent ion-exchange isotherms in zeolites X and Y

A numerical method of regularization has been used to effect the deconvolution of isotherms obtained from the literature describing the exchange of Li + K +, and Rb + into the synthetic faujasites NaX and NaY. The obtained selectivity coefficient distributions fit the univalent isotherms used for deconvolution. The relative number of K + cations undergoing exchange with the obtained selectivity coefficients has been compared with published cation-site populations in K-X and K-Y, determined crystallographically.

ChemInform Abstract: Catalytic Properties of Synthetic Faujasites Modified with Fluoride Anions.

Zeolite HAl–Y was modified by treatment with an aqueous solution of ammonium fluoride followed by calcination. Crystallinity was preserved in samples containing Al in large cavities. Fluorination brings about an increase in catalytic activity for cumene cracking, which is probably due to the interaction between the acidic structural hydroxy groups and AlF3 or other Al–F species created in the intracrystalline structure of the zeolite.

Catalytic properties of synthetic faujasites modified with fluoride anions

Zeolite HAl–Y was modified by treatment with an aqueous solution of ammonium fluoride followed by calcination. Crystallinity was preserved in samples containing Al in large cavities. Fluorination brings about an increase in catalytic activity for cumene cracking, which is probably due to the interaction between the acidic structural hydroxy groups and AlF3 or other Al–F species created in the intracrystalline structure of the zeolite.

Magic‐Angle‐Spinning NMR (MAS‐NMR) Spectroscopy and the Structure of Zeolites

AbstractAfter outlining the chemical features and properties which make zeolites such an important group of catalysts and sorbents, the article explains how high‐resolution solid‐state NMR with magic‐angle spinning reveals numerous new insights into their structure.29Si‐MAS‐NMR readily and quantitatively identifies five distinct Si(OAl)n(OSi)4‐nstructural groups in zeolitic frameworks (n = 0, 1,….4), corresponding to the first tetrahedral coordination shell of a silicon atom. Many catalytic and other chemical properties of zeolites are governed by the short‐range Si, Al order, the nature of which is greatly clarified by29Si‐MAS‐NMR. It is shown that, as expected from Pauling's electroneutrality principle and Loewenstein's rule, both in zeolite X and in zeolite A (with Si/Al = 1.00) there are no AlOAl linkages. In zeolite A and zeolite X with Si/Al = 1.00 there is strict alternation of Si and Al on the tetrahedral sites. Ordering models for Si/Al ratios up to 5.00 (in zeolite Y) may also be evaluated by a combination of MAS‐NMR experiments and computational procedures.29Si‐MAS‐NMR spectra reveal the presence of numerous crystallographically distinct Si(OSi)4sites in silicalite/ZSM‐5, suggesting that the correct space group for these related porosilicates is not Pnma.27Al‐MAS‐NMR clearly distinguishes tetrahedrally and octahedrally coordinated aluminum, proving that, contrary to earlier claims, Al in silicalite is tetrahedrally substituted within the framework. In combination,29Si‐ and27Al‐MAS‐NMR is a powerful tool for monitoring the course of solid‐state processes (such as ultrastabilization of synthetic faujasites) and of gas‐solid reactions (dealumination of zeolites with silicon tetrachloride vapor at elevated temperatures). They also permit the quantitative determination offrameworkSi/Al ratios in the region 1.00 < Si/Al < 10 000. Since most elements in the periodic table may be accommodated within zeolite structures, either as part of the exchangeable cations or as building units of the anionic framework, there is immense scope for investigation by MAS‐NMR and its variants (cross‐polarization, multiple pulse and variable‐angle spinning) of bulk, surface and chemical properties. Some of the directions in which future research in zeolite science may proceed are adumbrated.

Characterization of the silicon-aluminum distribution in synthetic faujasites by high-resolution solid-state silicon-29 NMR

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCharacterization of the silicon-aluminum distribution in synthetic faujasites by high-resolution solid-state silicon-29 NMRM. T. Melchior, D. E. W. Vaughan, and A. J. JacobsonCite this: J. Am. Chem. Soc. 1982, 104, 18, 4859–4864Publication Date (Print):September 1, 1982Publication History Published online1 May 2002Published inissue 1 September 1982https://doi.org/10.1021/ja00382a020RIGHTS & PERMISSIONSArticle Views380Altmetric-Citations103LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (680 KB) Get e-Alerts Get e-Alerts

Transition metal ion exchange in mixed ammoniumsodium X and Y zeolites

Ion-exchange characteristics of hydrated Cu 2+, Co 2+, Ni 2+, Mn 2+ and Zn 2+ ions in synthetic faujasites (X and Y) were examined at 25°C and at a total solution normality of 0.1 g equiv. dm −3. The original zeolites were samples of X and Y containing both ammonium and sodium ions. Evidence was found confirming earlier observations of significant irreversible binding of transition metals into the zeolites. Sodium ions which could not be removed by repeated exchanged of the zeolite with ammonium chloride solution were removed with relative ease by the transition metals, especially copper.

Catalytic properties of a PdCl2�CuC12/zeolite system in the oxidation of C2-C4 olefins to carbonyl compounds

1. Characteristic features of the catalytic action of the PdCl2·CuCl2/zeolite systems obtained by the impregnation method were studied during the oxidation of C2-C4 olefins to carbonyl compounds. In activity, selectivity, and stability, systems based on synthetic faujasites are superior to both the PdCl2 · CuCl2/ Al2O3 (SiO2; amorphous aluminosilicate) and the ion-exchange-produced PdCu zeolites already studied. 2. Conditions were found ensuring a 98–99% selectivity of the conversion of C2H4 to acetaldehyde, and C3H6 to acetone.

Exchange of ammonium and sodium ions in synthetic faujasites

Ion-exchange isotherms for the Na ⇌ NH4 equilibrium in zeolites X and Y were constructed at 298 K and a total solution normality of 0.1 g-equiv. dm–3. Values for the standard free energy of exchange were calculated and shown to be consistent with the affinity sequence predicted using dielectric theory. Comparisons are made between previously reported studies on the Na ⇌ NH4 exchange in X and Y and this current work, and the differences in experimental data are discussed. Statistical thermodynamic considerations provide a greater understanding of the Na ⇌ NH4 exchange equilibrium in X and Y, and collectively the evidence suggests that high framework charge and ion-sieving factors in X are the dominant properties determining exchange selectivity and maximum exchange levels in this zeolite. In Y, the ion-sieve effect and repulsion between the entering ammonium ions are the dominant factors.

A re-examination of Si, Al ordering in zeolites NaX and NaY

High-resolution solid-state 29Si nuclear magnetic resonance (n.m.r.) spectra were recorded at 79.80 MHz, with rapid spinning of the sample at the magic angle to the external magnetic field, for a series of phase-pure synthetic faujasites with Si/Al ratio in the range 1.19–2.75. On the basis of previous work which related 29Si chemical shift to environment, signal intensities corresponding to Si(nAl) structural units (n= 0, 1, 2, 3, 4) could be quantitatively determined by accurate deconvolution of the spectrally well-resolved Gaussian peaks. Even though n.m.r. spectra do not by themselves provide direct evidence for Si, Al ordering beyond the first tetrahedral coordination shell, from the observed ratio of intensities of Si(nAl) units and from arguments based on crystal symmetry and electrostatic energy, a series of Si, Al ordering schemes was constructed. These schemes offer greater insight into the structure of the aluminosilicate framework than can be achieved at present by other techniques. Inter alia, they reveal that the Loewenstein rule, which forbids Al atoms to occupy neighbouring framework tetrahedral sites, is strictly obeyed for zeolites of the faujasite structure. Our results and conclusions can also explain observed discontinuites in the plot of the (cubic) unit-cell parameter against aluminium content in terms of Si, Al ordering within the framework. Moreover, the magic-angle-spinning nuclear magnetic resonance (m.a.s.n.m.r.) spectra provide an independent method of determining Si/Al ratios: ratios determined by X-ray fluorescence or analytical electron microscopy agree within a few per cent with those derived from m.a.s.n.m.r., thus lending further credence to the value of solid-state n.m.r. in studies of aluminosilicates. The effect of second-nearest (tetrahedral) neighbours on chemical shifts, as well as the spectral and structural characteristics of faujasites possessing “non-ideal” Si/Al ratios, are also discussed.

Ordering of aluminium and silicon in synthetic faujasites

The distribution of aluminium and silicon atoms on the tetrahedral sites in synthetic faujasites (zeolites X and Y) has been debated for many years. Although the framework structure of the zeolite is known1, the detailed distribution of Si and Al in the lattice cannot be established by conventional methods, partly because of the very similar scattering powers of silicon and aluminium for X rays and partly because of the difficulties in obtaining crystals of adequate size and perfection. Some inferences have, however, been made on the basis of four indirect approaches: variation of the (cubic) lattice parameter as a function of aluminium content2,3; electrostatic calculations4; change of zeolitic acidity on successive extraction of aluminium from the framework5–7; and the kinetics of crystallization8. All these approaches have assumed the validity of ‘Loewenstein's rule’ which forbids Al atoms from occupying neighbouring tetrahedral sites. High-resolution solid-state 29Si NMR (with magic angle spinning) can determine the detailed Si, Al ordering in zeolites9–16 . NMR coupled with electron diffraction studies has revealed that Loewenstein's rule, generally treated as axiomatic, is broken in Linde A10,13,14 and in at least three other zeolites where Si/Al is nominally unity15. In view of its importance as an archetypal zeolite, particularly commercially, we have re-examined the question of framework ordering in faujasite. We propose new ordering schemes and explain discontinuities in the unit cell constant as a function of composition.

Mobility of magnesium ions in the synthetic zeolites A, X and 2.62-Y

Radiochemical methods have been used to study magnesium ion movements in the synthetic faujasites X and 2.62-Y as well as in zeolite A. Characterization of the magnesium exchanged forms of the zeolites has been carried out. Self-diffusion parameters measured have been compared to those of the other alkaline earths and to those of transitional elements where appropriate. Conclusions have been made as to likely mechanisms for the observed magnesium ion migrations.

Study of oxygen mobility in some synthetic faujasites by isotopic exchange with carbon dioxide

Oxygen isotopic exchange between CO/sub 2/ and Na-Y, Na-X, and the germanic homologue of Na-X was studied at 25 to 500/sup 0/C by mass-spectrometric analysis of the change in the /sup 18/O//sup 16/O ratio in the gas circulated across the zeolite. Infrared spectra of CO/sub 2/ adsorption and reaction with the X zeolites were obtained under similar experimental conditions. Isotopic exchange is measurable in all of the zeolites at room temperature. However, exchange in Na-X and NaGe-X was much more rapid under comparable conditions than exchange in Na-Y. This difference in behavior must be attributed to the effects associated with the substitution of Al/sup 3 +/ and Ge/sup 4 +/ for Si/sup 4 +/ in the tetrahedral sites of X zeolites. In particular, the infrared results demonstrate that various chemisorbed carbonate species can form on the X varieties. Isotopic exchange is promoted by some of these species, whereas others can evidently block active exchange sites on the zeolite surface. The absence of chemisorbed CO/sub 2/ species on Na-Y accounts for the relatively low rate of exchange in this molecular sieve.

The Catalytic Activity of Cu2+‐Ions in Zeolites as Compared to Bulk Oxides of Copper

AbstractThe kinetics of oxidation of CO and of C3H8 with excess oxygen have been investigated on different Cu2+‐containing catalysts: CuO. CuAl2O4, Cu3TiO5, CuCr2O4, CuMn2O4 and several Cu2+ ‐exchanged synthetic faujasites (Y) and mordenites in the temperature range from 330 K to 780 K. Both reactions are first order in CO or C3H8, resp. Rate coefficients have been evaluated per unit of mass, per unit of BET‐surface area for the bulk oxides and per unit amount of CO‐chemisorption sites. ‐ On the bulk oxides the surface‐specific rate is higher for CuO, CuMn2O4, and CuCr2O4 than for CuAl2O4 and Cu3 TiO5. The turnover‐numbers per CO‐chemisorption‐site are 2 to 4 orders of magnitude smaller for Cu2+ ‐containing zeolites than for CuO, CuMn2O4 or CuCr2O4.

Some studies on cerium exchanged synthetic faujasites

Radiochemical techniques have been used to measure cation mobilities in samples of NaCeX zeolite which have been subjected to calcinations in air or nitrogen. Thermal analyses and X-ray powder photographs were used to determine changes in water content and/or crystallinity.

Heat of adsorption of ammonia by type E zeolites

1. Measurement has been made of the heat evolved in the adsorption of ammonia on calcium, calcium-sodium, and sodium forms of type E zeolites. 2. The Ca2+ cations of type E zeolites are more active which respect to adsorbing ammonia molecules than are the Ca2+ ions of synthetic faujasites and type A zeolites. 3. The results obtained are analyzed in terms of lattice position differences in the calcium cations, of the type E zeolites and of zeolites of other types.

Spectroscopic characterization and thermal stability of copper(II) ethylenediamine complexes on solid surfaces. 1. Synthetic faujasites types X and Y

Spectroscopic characterization and thermal stability of copper(II) ethylenediamine complexes on solid surfaces. 1. Synthetic faujasites types X and Y