催化剂量甘油对THF-FER沸石结晶过程的加速作用

The hydrothermal crystallization of THF-FER zeolite was investigated in the reactant system of Na2O-SiO2-Al2O3-H2O with tetrahydrofuran （THF） as the template in the presence of various catalytic amount of glycerol [CH2（OH）CH（OH）CH2（OH）, Glyc] in the temperature range of 413--473 K. Powder X-ray diffraction （XRD） was used to observe the crystallization process, and scanning electron microscope （SEM）, ^13C cross polarization （CP） and ^27Al magic angle spinning nuclear magnetic resonance （MAS NMR）, X-ray fluorescence scattering spectroscopy （XRF）, thermal analysis and nitrogen sorption were used to characterize the zeolite synthesized in the reactant system with Glyc. The catalytic amount of Glyc could promote the crystallization of FER zeolite, to result in lowering the reaction temperature, shortening the period of the zeolite crystallization and effectively restraining cocrystallization of MOR zeolite as an impure phase especially at low reaction temperature, and possess a significant effect on the morphology and the crystal size of TI-IF-FER zeolite.     

High-resolution 27Al NMR study of the states of aluminum atoms in modified natural mordenite

High-resolution ²⁷Al NMR has been applied to the states of aluminum in modified natural mordenite. Acid treatment of the natural mordenite and heat treatment of the ammonium form alter the coordination state of 6–8% of the aluminum atoms from tetrahedral (in the framework) to octahecral (at the inner surfaces of the zeolite cavities). In that state, the aluminum can exchange with Na⁺, NH₄ ⁺, and other cations. This change in coordination state should have a considerable effect on the catalytic parameters of zeolites.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 2, pp. 241–244, March–April, 1987.     

Triterpene glycosides of Hedera taurica VI. Structures of hederosides G,H1, H2, and I from the berries of Crimean ivy

We have isolated from Crimean ivy berries in addition previously known triterpene glycosides — 3-O-α-L-arabinopyranosyl-28-O-[O-α-L-rhamnopyranosyl-(1 → 4)-O-β-D-glycopyranosyl-(1 → 6)-β-D-glucopyranosyl]hederagenin, 3-O-[O-α-L-rhamnopyranosyl-(1 → 2)-α-L-arabinopyranosyl]-28-O-[O-α-L-rhamnopyranosyl-(1 → 4)-O-β-D-glucopyranosyl-(1 → 6)-β-D-glycopyranosyl]hederagenin, the new triterpene glycosides hederoside H₂-3-O-[O-β-D-glycopyranosyl-(1 → 2)-β-D-glycopyranosyl-(1 → 2)-β-D-glucopyranosyl]-28-O-[O-β-D-glucopyranosyl-(1 → 6)-β-D-glucopyranosyl]oleanolic acid- and hederoside I-3-O-[O-β-D-glucopyranosyl-(1 → 2)-β-D-glucopyranosyl]-28-O-[O-β-D-glucopyranosyl-(1 → 6)-β-D-glucopyranosyl]hederagenin. Details of their¹³C NMR spectra are given. M. V. Frunze Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 779–783, November–December, 1990.     

Investigations of TsVM zeolite acidities with different degrees of exchange of Na+ by H+

The method of programmed thermal desorption of ammonia has been used to establish that on the surface of the sodium form of type TsVM zeolite having a modulus SiO₂/Al₂O₃= 34.5 there are two types of acidic centers having ammonia desorption activation energies E_d equal to 40–45 and 80–100 kJ/mole. Replacement of Na⁺ by H⁺ leads to the appearance of a third type of center with a value E_D=130–150 kJ/mole. In this case in the IR spectra of specimens saturated with ammonia a band appears at 1410 cm_–1, which is evidence for the presence of NH ₄ ⁺ ions. Increasing the degree of Na⁺ replacement by H⁺ leads to a nonproportional rapid increase in the concentration of highly energetic centers, which may be explained by the partial transfer of aluminum into cationic positions with the formation of additional acidic centers.Translated from Teoreticheskie i Éksperimental'naya Khimiya, Vol. 22, No. 6, pp. 752–755, November–December, 1986.     

Thermal transformations in systems based on zeolites Y,X, and A containing zinc and sodium nitrates

Thermal transformations in systems formed by interaction of Zn and Na nitrates with Y, X, and A zeolites were studied by TG—DTA technique. Temperature regions of existence of adsorbed water, water of crystallization, and decomposition of NO₃ ^– anion were determined. These intervals depend on the composition, structure, method of preparation, and pre-treatment conditions of zeolite systems. The extent of NO₃ ^– decomposition depends not only on the zinc and sodium content but also on the presence of ammonia involved in NO₃ ^– reduction. The zeolite matrix strongly stabilizes the occluded NO₃ ^– anions. A portion of zinc oxide formed by zinc nitrate decomposition is probably localized inside the zeolite cavities as the [Zn—O—(ZnO) _n —Zn]²⁺ particles. The latter compensate charges of the isolated [AlO₄]^– tetrahedra.     

Comparative FT infrared study of structural changes occuring on dealumination of zeolite Na-Y with ethylenediaminetetraacetic or hydrochloric acid

IR lattice vibration spectra were used to monitor the changes in the structure of zeolite Na-Y upon its dealumination with ethylenediaminetetraacetic acid (EDTA) or with HCl. The terminal Si-O(H,Na) bonds thus formed (which are detectable by characteristic absorbance at v 900–950 cm^–1) are energetically less uniform when EDTA has been used as the dealuminating agent. This inhomogeneity is connected with the local deformations of zeolite structure which result in lowering the symmetry of silicon-oxygen tetrahedra. As a consequence, two novel bands appear at v 1090 cm^–1 and 1200 cm^–1 in addition to the fundamental absorption bands, v_as (TO₄) (T = Si, Al), at 1030 cm^–1 and 1145 cm^–1. A mechanism of dealumination is proposed, which takes into account the topochemical peculiarities involved in the chelation of the framework aluminum ions with EDTA.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskay, No. 2, pp. 284–287, February, 1993.     

Synthesis of highly ordered cubic zeolite A and its ion-exchange behavior

Well-ordered cubic zeolites 4A were synthesised using sol–gel process in the presence of different silica and aluminum sources. The aluminum and silica sources determined whether or not zeolites were formed at precise silica/alumina mole ratio. Zeolites were formed only when the aluminum source was sodium aluminate, the silica source was fumed silica, colloidal silica or sodium metasilicate. Our findings indicated that the type of zeolite invariably obtained was 4A and SEM images indicated that the produced zeolites are cubic shaped crystals with planar surfaces and well-defined edges and sharp crystals. In turn, synthesis parameters are seen to have a significant effect in maximizing heavy metals uptake (for example Cu²⁺, Cr³⁺, Cd²⁺ and Ni²⁺) by synthesized zeolites. Zeolite 4A gave better heavy metal uptakes than amorphous or non-zeolite crystalline materials. This was attributed to higher ion-exchange capacity and higher BET specific surface area 445 m²/g and pore volume 0.141 cm³/g. The latter attribute possibly translates to greater accessibility of ion-exchange sites and selectivity towards metal type by this zeolite followed the sequence: Cu²⁺ > Cr³⁺ ≥ Cd²⁺ > Ni²⁺.     

Sorption-desorption of radiocesium on various sorbents in presence of humic acid

In general, the amount of radiocesium sorbed by the five sorbents with 0.01 mol·dm^–3 NaCl was in order zeolite > NiFeCN–SiO₂ > montmorillonite > aerogel > silica gel. Addition of humic acid solution to the sorbents depressed the sorption of cesium by all sorbents, except for NiFeCN–SiO₂ was not seen, with the greatest effect showing to the aerogel. The presence of humic acid resulted in an enhanced desorption of cesium from zeolite, NiFeCN–SiO₂ and to a lesser extent from montmorillonite and silica gel. The order of cesium retention following desorption for both sorbent and sorbent/humic-acid mixtures was zeolit > NiFeCN–SiO₂ > montmorillonite > silica gel. The presence of humic acid resulted in decreasing of distribution coefficient values for both sorption and desorption processes.     

Eco-friendly synthesis of high silica zeolite Y with choline as green and innocent structure-directing agent

Zeolite synthesis in contemporary chemical industries is predominantly conducted using organic structure-directing agents (OSDAs), which are chronically hazardous to humans and the environment. It is a growing trend to develop an eco-friendly and nuisanceless OSDA for zeolite synthesis. Herein, choline is employed as a non-toxic and green OSDA to synthesize high silica Y zeolite with SiO₂/Al₂O₃ ratios of 6.5–6.8. The prepared Y zeolite samples exhibited outstanding (hydro)thermal stability at ultrahigh temperature owing to the higher SiO₂/Al₂O₃ ratio. The XRF, SEM, ²⁹Si-NMR and ¹³Na+ results suggested that choline plays a structure-directing role in the synthesis of Y zeolite, while the feed molar fraction of Na⁺ is a crucial determinant for the framework SiO₂/Al₂O₃ ratio and the crystal morphology.     

Specific Sorption Sites for Nitrogen in Zeolites NaLSX and LiLSX

Specific sorption sites for nitrogen, N₂, in NaLSX and LiLSX zeolites were investigated using a DRIFT spectroscopic method. Sorption of molecular hydrogen, H₂, by NaLSX or LiLSX zeolite at 77 K with DRIFT control of perturbation of sorbed molecules allowed to discriminate two or three different types of specific sorption sites in the respective zeolites. Their H–H stretching frequencies are 4077 and 4081 cm^–1 for NaLSX, and 4061, 4084 and 4129 cm^–1 for LiLSX. With reference to an independent investigation by methods of both sorption thermodynamics and molecular modeling for N₂ sorption on LiLSX, the first two of the corresponding bands were ascribed to H₂ sorption on lithium cations, Li⁺, localized in supercages of the faujasite, FAU, zeolite framework at sites SIII and SIII, while the latter band most likely belongs to H₂ sorption on Li⁺ cations at sites SII, and on hydroxyl groups, OH. Sorption of N₂ by Li⁺ cations at sites SIII and SIII is the strongest, resulting in a decrease of intensity of the corresponding DRIFT bands that stem from subsequent H₂ sorption. Nitrogen sorption by Li⁺ cations at sites SII is much weaker. Sorption of N₂ on Na⁺ cations at sites SIII in NaLSX zeolite is also stronger than by Na⁺ cations at sites SII.     

An aqueous thermodynamic model for a high valence 4∶2 electrolyte Th4+−SO 4 2− in the system Na+−K+−Li+−NH 4 + −Th4+−SO 4 2− −HSO 4 − −H2O to high concentration

An aqueous thermodynamic model that is valid from zero to high concentration is proposed for the Na⁺–K⁺–Li⁺–NH ₄ ⁺ –Th⁴⁺–SO ₄ ^2– –HSO ₄ ^– –H₂O system. The model is based on the aqueous ion-interaction model of Pitzer and coworkers. The thorium sulfate complex species Th(SO₄)₂(aq) and Th(SO₄) ₃ ^2– are also included in the model. The final thermodynamic model presented here accurately predicts all reliable thermodynamic data, including solvent extraction and solubility data, for the Na⁺–K⁺–Li⁺–NH ₄ ⁺ –Th⁴⁺–SO ₄ ^2– –HSO ₄ ^– –H₂O system to high concentration. The aqueous thermodynamics of high-valence (3:2, 4:2), electrolytes are complicated by very strong specific ion interactions or ion pairing in dilute solution and by an effective redissociation of aqueous complex species at high concentration. Methods of treating these complications, in terms of valid aqueous thermodynamic models, are discussed in detail for the high-valence Th⁴⁺–SO ₄ ^2– –H₂O system.     

Framework Effects on Activation and Functionalisation of Methane in Zinc-Exchanged Zeolites

The first selective oxidation of methane to methanol is reported herein for zinc-exchanged MOR (Zn/MOR). Under identical conditions, Zn/FER and Zn/ZSM-5 both form zinc formate and methanol. Selective methane activation to form [Zn-CH₃]⁺ species was confirmed by ¹³C MAS NMR spectroscopy for all three frameworks. The percentage of active zinc sites, measured through quantitative NMR spectroscopy studies, varied with the zeolite framework and was found to be ZSM-5 (5.7 %), MOR (1.2 %) and FER (0.5 %). For Zn/MOR, two signals were observed in the ¹³C MAS NMR spectrum, resulting from two distinct [Zn-CH₃]⁺ species present in the 12 MR and 8 MR side pockets, as supported by additional NMR experiments. The observed products of oxidation of the [Zn-CH₃]⁺ species are shown to depend on the zeolite framework type and the oxidative conditions used. These results lay the foundation for developing structure–function correlations for methane conversion over zinc-exchanged zeolites.     

Ion-exchange chromatography using vanadyl and vandate salts as mobile phases with indirect detection

Summary Vanadyl sulfate, VOSO₄, was characterized as the mobile phase for the ion exchange separation of Li⁺, Na⁺, NH ₄ ⁺ , and K⁺ using indirect photometric detection at 254 nm. Detection limits ranged from 0.2 ppm for Li⁺ to 1 ppm for K⁺. Indirect electrochemical detection of these separated cations by reduction of VO (II) to V³⁺ was compared to spectrophotometric detection. The potential of the vanadate species, HVO ₄ ^2– , for the separation of F^–, Cl^–, and SO ₄ ^2– , with indirect photometric detection was also demonstrated.     

Diffusion with hydrolysis and ion association in aqueous solutions of beryllium sulfate

Taylor dispersion is used to measure mutual diffusion coefficients for aqueous solutions of beryllium sulfate at concentrations from 0.005 to 1 mol-L^–1 at 25°C. Least-squares analysis of the dispersion profiles shows that diffusion of the partially hydrolyzed salt produces a small additional flow of sulfuric acid, about 0.04 mol sulfuric acid per mole of total beryllium sulfate. Ternary diffusion coefficients measured for the aqueous BeSO₄–H₂SO₄ system are qualitatively consistent with Nernst-Planck predictions based on the formation of beryllium sulfate ion pairs, bisulfate ions, and the hydrolysis equilibria 2Be²⁺+H₂O= Be₂OH³⁺+H⁺, 3Be²⁺+2H₂O=Be₃(OH) ₂ ⁴⁺ +2H⁺. Except for very dilute solutions, the predicted flow of sulfuric acid is small compared to the flow of beryllium sulfate because most of the beryllium ions are protected from hydrolysis by the formation of BeSO₄ ion pairs, and most of the hydrogen ions produced by hydrolysis are converted to less-mobile bisulfate ions.     

Kinetic,solvation and reactivity studies of iron(II) complexes of monoxime and dioxime ligands

Complexes of Fe^II with monoxime and dioxime ligands have been isolated and characterised. Kinetic results and rate laws are reported for acid aquation and base hydrolysis of these complexes in H₂O and in MeOH–H₂O mixtures. Kinetics of acid catalysed aquation of Fe^II–monoxime complexes follow a rate law with k_obs = k₂[H⁺] + k₃[H⁺]², while kinetics of acid dissociation and base hydrolysis of the Fe^II–dioxime complex follow rate laws with k_obs = k₂[H⁺] and k_obs = k₂[OH⁻]. Acid aquation and base hydrolysis mechanisms are proposed. The solubilities of Fe^II–monoxime and –dioxime complex salts are reported and transfer chemical potentials of their complex cations are calculated. Solvent effects on reactivity trends have been analysed into initial and transition state components. These are determined from transfer chemical potentials of reactant and kinetic data. Rate constant trends from these complexes are compared and discussed in terms of ligand structure and solvation properties. Our kinetic results give information relevant to the application of these ligands as analytical reagents for trace Fe^II in acidic and neutral media, in water and in aqueous alcohols.     

Some reactions of dimethyl tin bis-S,S′ -(O-sodium thiosulfate) and the structure of its complex with dibenzo-18-crown-6

The reactions of the title compound, Me₂Sn(S-SO₃Na · H₂O)₂, with alkyliodides and trimethyltin chloride in an aqueous medium, as well as with dibenzo-18-crown-6 (DB-18-C-6) in acetone have been studied. The iodides RI (R = Me, Et) attack both of the tin—sulfur bonds to give dimethyltin diiodide and the respective disulfides, R₂S₂. Trimethyltin chloride enters an exchange reaction which involves sodium ions and affords Me₂Sn(S-SO₃SnMe₃)₂ as the reaction intermediate; the latter decomposes to ultimately give trimethyltin sulfate, dimethyltin thiosulfite, and elemental sulfur. An ionic complex, [Me₂Sn(S-SO₃)₂]₂ ^2–[Na(DB-18-C-6)(Me₂CO)]⁺[Na(DB-18-C-6)(Me₂CO)(H₂O)]⁺, soluble in acetone and methylene chloride has been also synthesized, and its structure has been determined by means of X-ray techniques.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 962–966, May, 1993.     

Desilication mechanism revisited: highly mesoporous all-silica zeolites enabled through pore-directing agents

The role of pore‐directing agents (PDAs) in the introduction of hierarchical porosity in silicalite‐1 in alkaline medium was investigated. By incorporation of various PDAs in aqueous NaOH, homogenously distributed mesopores were introduced in 2.5 μm silicalite‐1 crystals. It was proven for the first time that framework aluminum is not a prerequisite for the introduction of intracrystalline mesoporosity by desilication. The pore‐directing role is not directly exerted by framework trivalent cations metals, but by species on the external surface of the zeolite. The inclusion of metal complexes (Al(OH)₄^?, Ga(OH)₄^?) and tetraalkyl ammonium cations (tetramethyl ammonium (TMA⁺), tetrapropyl ammonium (TPA⁺)) in the alkaline solution led to distinct mesopore surface areas (up to 286 m² g^?1) and pore sizes centered in the range of 5–20 nm. In the case alkaline treatment was performed in the presence of Al(OH)₄^?, all aluminum partially integrated in the zeolite giving rise to both Lewis and Brønsted acidity. Apart from the concentration and location, the affinity of the PDA to the zeolite surface plays a crucial role in the pore formation process. If the PDA is attracted too strongly (e.g., TMA⁺), the dissolution is reduced dramatically. When the pore‐directing agent is not attracted to the zeolite’s external surface, excessive dissolution occurs (standard alkaline treatment). TPA⁺ proved to be the most effective PDA as its presence led to high mesopore surface areas (>200 m² g^?1) over a broad range of PDA concentrations (0.003–0.1 M ). Importantly, our results enable to extend the suitability of desilication for controlled mesopore formation to all‐silica zeolites.     

Strontium and cesium sorption of some Anatolian zeolites

Zeolite samples of Tertiary age obtained from different areas of Anatolia (Turkey) are classified as Clinoptilolite, Analcime or Heulandite and we have investigated their sorption capacity for Cs⁺ and Sr²⁺ ions from aqueous solutions. Quantitative analysis of the zeolite samples untreated and treated with chloride salts of Cs⁺ or Sr²⁺ in aqueous solutions, for Na, Mg, Al, Si, P, K, Ca, Ti, Mn and Fe were performed using EDXRF. Chemical analysis indicated that the Clinoptilolite type zeolite from the deposits of Cankiri-Corum Basin of Anatolia is the best sorber for Sr and Cs ions.Presented at the Sixth International Seminar on Inclusion Compounds, Istanbul, Turkey, 27–31 August, 1995.     

Effect of thermal and acid treatment on the structure of NH4Na—Y zeolite by IR data

The structural transformations of ammonium-exchanged forms of Na-Y zeolite during thermal evacuation and acid treatment were studied using IR spectroscopy. The formation of the zeolite H-forms by shallow-bed evacuation of NH₄N-Y at 570 K is accompanied by a high-frequency shift of the bands in the IR lattice vibration spectra. In the formation of the H⁺-forms resulting from the decationization of zeolite by treatment with an aqueous HCl solution, no shifts of the bands are observed. During deep-bed calcination in air the H⁺-form, is transformed into the H-form completed by the formation of a highly-crystalline stabilized zeolite at 623 K. A rapid increase in the shallow-bed calcination temperature results in a collapse of the structure of the H- and H⁺-forms followed by the formation of amorphous SiO₂.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 236–240, February, 1995.     

IR Spectra of Ethane Adsorbed on the Hydrogen,Sodium, and Zinc Forms of a Y-Type Zeolite: Interpretation Using <Emphasis Type="Italic">ab initio</Emphasis> Quantum Chemical Calculations

Ethane adsorption on the hydrogen, sodium, and zinc forms of faujasite brings about polarization anisotropy of the C-H stretching vibrations. This anisotropy shows itself most clearly as perturbation of the vibrational mode analogous to the breathing C-H mode ν₁ of free ethane. The relative intensity and the low-frequency shift of the absorption band due to the distorted ν₁ mode increase with increasing perturbation caused by the C₂H₆-adsorption site interaction. The polarizing power of adsorption sites increases in the order H⁺ < Na⁺ < Zn²⁺. The C-H stretching vibrations in ethane adsorbed on the cationic forms of the Y zeolite are not symmetry-forbidden; accordingly, adsorbed ethane gives more absorption bands than gaseous ethane. The interaction between ethane and zinc cations in the Y zeolite structure eliminates not only the symmetry forbiddenness but also the twofold degeneracy of the C-H stretches.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 434–440.Original Russian Text Copyright © 2005 by Pidko, Kazanskii.