Ammonium-exchanged Zeolite Research Articles

Local probes show that framework modification in zeolites occurs on ammonium exchange without calcination

Framework modification involving a change in the Al environment from tetrahedral to octahedral is frequently reported in ammonium-exchanged zeolites after calcination, steaming, acid wash and other harsh treatments. We characterized Na-Y and partially exchanged NH4-Y zeolites by spectroscopic and diffraction methods in order to determine if NH4 exchange itself causes framework modification. High-resolution MAS SS NMR data show that even without calcination, some Al atoms change their local environment from tetrahedral to octahedral. PDF analysis corroborates this change and shows an increase in the aluminium coordination number. TEM images show no significant change in morphology of the crystallites, and no major changes in crystallinity are detected by X-ray diffraction. A similar result is obtained on Na-A zeolite suggesting that such increase in the coordination number of Al atoms during the exchange is a common feature in zeolites. Local probes, NMR and PDF analysis show changes in the local environments of Al atoms in the framework, which are usually not possible to see in the average structure.

Oxidative dehydration of glycerol to acrylic acid over vanadium-impregnated zeolite beta

The oxidative dehydration of glycerol to acrylic acid was studied over vanadium-impregnated zeolite Beta. Catalysts were prepared by wet impregnation of ammonium metavanadate over ammonium-exchanged zeolite Beta, followed by air calcination at 823 K. Impregnation reduced the specific surface area, but did not significantly affected the acidity (Brønsted and Lewis) of the zeolites. The catalytic evaluation was carried out in a fixed bed flow reactor using air as the carrier and injecting glycerol by means of a syringe pump. Acrolein was the main product, with acetaldehyde and hydroxy-acetone (acetol) being also formed. Acrylic acid was formed with approximately 25% selectivity at 548 K over the impregnated zeolites. The result can be explained by XPS (X-ray photoelectron spectroscopy) measurements, which indicated a good dispersion of the vanadium inside the pores.

Single-crystal Structure of Fully Dehydrated and Largely NH4+-exchanged Zeolite Y (FAU, Si/Al = 1.70), │(NH4)60Na11│[Si121Al71O384]-FAU

The single-crystal structure of largely ammonium-exchanged zeolite Y dehydrated at room temperature (293 K) and 1 <TEX>${\times}\;10^{-6}$</TEX> Torr. has been determined using synchrotron X-radiation in the cubic space group <TEX>$Fd\overline{3}m\;(a=24.9639(2)\AA)$</TEX> at 294 K. The structure was refined to the final error index <TEX>$R_1$</TEX> = 0.0429 with 926 reflections where <TEX>$F_o>4\sigma(F_o)$</TEX>; the composition (best integers) was identified as |<TEX>$(NH_4)_{60}Na_{11}$</TEX>|[<TEX>$Si_{121}Al_{71}O_{384}$</TEX>]-FAU. The 11 <TEX>$Na^{+}$</TEX> ions per unit cell were found at three different crystallographic sites and 60 <TEX>${NH_4}^{+}$</TEX> ions were distributed over three sites. The 3 <TEX>$Na^{+}$</TEX> ions were located at site I, the center of the hexagonal prism (<TEX>$Na-O\;=\;2.842(5)\;\AA\;and\;O-Na-O\;=\;85.98(12)^{\circ}$</TEX>). The 4 <TEX>$Na^{+}$</TEX> and 22 <TEX>${NH_4}^{+}$</TEX> ions were found at site I' in the sodalite cavity opposite the double 6-rings, respectively (<TEX>$Na-O\;=\;2.53(13)\;\AA,\;O-Na-O\;=\;99.9(7)^{\circ},\;N-O\;=\;2.762(11)\;\AA,\;and\;O-N-O =\;89.1(5)^{\circ}$</TEX>). About 4 <TEX>$Na^{+}$</TEX> ions occupied site II (<TEX>$(Na-O\;=\;2.40(4)\;\AA\;and\;O-Na-O\;=\;108.9(3)^{\circ}$</TEX>) and 29 <TEX>${NH_4}^{+}$</TEX> ions occupy site II (<TEX>$N-O\;=\;2.824(9)\;\AA\;and\;O-N-O\;=\;87.3(3)^{\circ}$</TEX>) opposite to the single 6-rings in the supercage. The remaining 9 <TEX>${NH_4}^{+}$</TEX> ions were distributed over site III' (<TEX>$N-O\;=\;2.55(3),\;2.725(13)\;\AA\;and\;O-N-O\;=\;94.1(13),\;62.16(15),\;155.7(14)^{\circ}$</TEX>).

Micro-cubic glass from pseudomorphism after thermal treatment of ammonium-exchanged zeolite A

Isothermal treatments of the ammonium-exchanged Na–zeolite A were carried out at 400 °C for different durations up to 1000 min in the air. The products were characterized by XRD, SEM, AFM, FT-IR, DTA and nitrogen adsorption measurement. The results confirmed that the amorphous pseudomorphism occurred, showing the tweed-like patterns on the surfaceof cubic solid. These characterizations supported the existence of thin surface layer of zeolite crystal as a microvessel,which was consistent with the previous hypothesis. The amorphous transformation was taking place by the mechanism, in which the zeolite framework reacted with hydrogen decomposed from ammonium ions. The obtained micro-cubic glass should be useful as an eco-functional material, such as the fixation of harmful ions.

Kinetic Parameters of Polyethylene Degradation by the Natural Zeolite Chabazite

High-density polyethylene (PE) was subjected to thermal degradation alone and in the presence of an ammonium-exchanged zeolite chabazite (CHA/PE). The processes were carried out in a reactor connected online to a gas chromatograph/mass spectrometer in order to analyse the evolved products. Polymer degradation was also evaluated by thermogravimetry, from room temperature up to 800°C, under a dynamic nitrogen atmosphere, with multiple heating rates. From the TG curves, the activation energy relating to the degradation process was calculated by using the Flynn and Wall multiple heating rate kinetic model for pure PE and for CHA/PE. The exchanged chabazite exhibited good selectivity for the catalytic degradation of PE to low molecular mass hydrocarbons.

Characterization and removal of extra lattice species in faujasites

The acidic properties of dealuminated Y-type zeolites were characterized by infrared (IR) spectroscopy, microcalorimetry, 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and temperature-programmed desorption (TPD). Microcalorimetric measurements exhibited a uniform heat of adsorption (140 kJ/mol) of ammonia on the strong Brönsted acid sites. The differences in the acid site concentrations measured by adsorption of ammonia from the gas phase and by decomposition of ammonium-exchanged zeolites are discussed. The results indicate that parts of the extra lattice material consisting of cationic aluminium oxide species or silica alumina species are removed by ion exchange with aqueous solutions of ammonium hydroxide. Based on this, a method for the controlled removal of extra lattice material was developed.

Preparation, characterization and photoreactivity of titanium(IV) oxide encapsulated in zeolites

The preparation, characterization and photoreactivity of titanium(IV) oxide encapsulated inside either sodium- or ammonium-exchanged zeolite Y (NaY and NH4Y), mordenite (NaM and NH4M) or potassium zeolite L (KL) are presented. The material was prepared by an ion-exchange method with ammonium titanyl oxalate monohydrate aqueous solution, (NH4)2TiO(C2O4)2·H2O. The results of X-ray photoelectron spectroscopy, chemical analysis and photolysis studies support the contention that the exchanged titanium species locate dominantly inside the zeolite cavities, and not on the external surfaces. The TiO2+-exchanged zeolite exhibits characteristics of TiO2, such as photoreduction of methyl viologen to methyl viologen radical cation. A significant blue shift of the UV–VIS reflectance spectrum (onset ca. 330 nm), compared with those of bulk anatase and rutile TiO2, and a lack of an X-ray diffraction pattern of TiO2 in the TiO2–zeolite samples indicate that the particle size of the TiO2 encapsulated inside the zeolite is on the nanometre scale.

Ethylene glycol—dimethyl carbonate cogeneration

In this paper eight classes of effective, and in most cases novel, transesterification catalysts are identified for the cogeneration of ethylene glycol plus dimethyl carbonate from ethylene carbonate and methanol. They include: (a) macroreticular and gel-type exchange resins with tertiary amine and quaternary ammonium pendant groups, (b) zirconium, titanium and tin homogeneous catalysts, (c) homogeneous Group VB and VIB compounds, (d) alkali metal silicates on silica, (e) ammonium-exchanged zeolites, (f) acidic resins bearing sulfonic acid and carboxylic acid functional groups and (g) tertiary phosphine polymer catalysts. Liquid products comprising in many cases near-equilibrium concentrations of ethylene glycol and dimethyl carbonate have been cogenerate in⩾ 98 mol% selectivity (based on EC converted) using continuous unit equipment under moderate conditions (60–150 °C, 100 psi). Unreacted methanol plus EC make up >99% of the remaining organics. The relative performance advantages and mechanistic pathways of these different classes of catalyst are compared and discussed.

Low-temperature Plasma Calcination of Zeolite NH 4, Na-Y

70% Ammonium-exchanged zeolite NH 4, Na-Y is completely deammoniated by low-temperature plasma calcination, while the crystallinity of the samples is not impaired. Neither the plasma calcined nor shallow bed treated material is “pure H-Y” zeolite, and 27Al MAS NMR indicates a slight dealumination of the zeolitic framework in each case. Hydronium ion exchange to product H,Na-Y from Na-Y using highly dilute acidic medium also resulted in partial dealumination of the sample. Plasma calcination of 87% ammonium-exchanged NH 4, Na-Y caused a severe loss of crystallinity, possibly because of mineral acid formation at inaccessible sites. Low-temperature plasma calcination is a mild technique for the oxidative removal of ammonia as long as oxidation products can easily leave the crystallite.

ChemInform Abstract: CRYSTAL STRUCTURE OF VACUUM‐DEHYDRATED FULLY AMMONIUM‐EXCHANGED ZEOLITE A

Chemischer InformationsdienstVolume 12, Issue 38 Physical Inorganic Chemistry ChemInform Abstract: CRYSTAL STRUCTURE OF VACUUM-DEHYDRATED FULLY AMMONIUM-EXCHANGED ZEOLITE A L. B. MCCUSKER, L. B. MCCUSKERSearch for more papers by this authorK. SEFF, K. SEFFSearch for more papers by this author L. B. MCCUSKER, L. B. MCCUSKERSearch for more papers by this authorK. SEFF, K. SEFFSearch for more papers by this author First published: September 22, 1981 https://doi.org/10.1002/chin.198138003AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume12, Issue38September 22, 1981 RelatedInformation

The crystal structure of vacuum-dehydrated fully ammonium-exchanged zeolite A

The crystal structure of vacuum-dehydrated fully ammonium-exchanged zeolite A

Crystal structure of vacuum-dehydrated fully ammonium-exchanged zeolite A

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCrystal structure of vacuum-dehydrated fully ammonium-exchanged zeolite ALynne B. McCusker and Karl SeffCite this: J. Am. Chem. Soc. 1981, 103, 12, 3441–3446Publication Date (Print):June 1, 1981Publication History Published online1 May 2002Published inissue 1 June 1981https://doi.org/10.1021/ja00402a031RIGHTS & PERMISSIONSArticle Views116Altmetric-Citations16LEARN 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 (819 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

The deammoniation reaction of ammonium X zeolite

The deammoniation of fully ammonium-exchanged zeolite X has been studied using differential thermal analysis. Deammoniation is shown to occur in two endothermic steps that correspond to the release of NH 3 from ammonium ions in small- and large-pore systems, respectively. Dehydroxylation of the resultant hydrogen-X zeolite occurs at a relatively low temperature of 175 °C. The thermograms of NH 4X and NH 4Y deamnoniation are compared.

Structural stability of partially ammonium-exchanged zeolite A

The thermal stability of the crystal structure of NaHA increases rapidly when the ratio of Na/Al rises above 0.33. The least damage to the structure occurs at a slow heating rate in a dry atmosphere. The hydrothermal stability of NaHA increases at a ratio of Na/Al in the range of 0.5 to 0.7. Both stabilities depend on the number of cation equivalents per unit cell, not on the number of cations. Zeolite A that is partially in the hydrogen form and thermally stable, can tolerate the sorption of small amounts of water and recalcination without losing crystallinity.