Infrared spectroscopic methodsfor the measurement of adsorption and adsorption kinetics of some aromatics (benzene, ethylbenzene, p-xylene), pyridine, and paraffins in solid microporous materials such as zeolites (MOR, ZSM-5, silicalite-1) are described as well as the evaluation of the spectroscopically obtained data. The adsorption isotherms are of the Langmuir-Freundlich type. Isosteric heats of adsorption, transport diffusivities, and activation energies of diffusion as deduced from the spectroscopic measurements are compared with literature data as far as available, and they are found to be in reasonable agreement with results provided by independent techniques. Special attention is paid to sorption and sorption kinetics of binary mixtures, especially the problems of co- and counter-diffusion.The design and application of a very promising novel technique for the measurement of sorbate transport in porous materials, viz. diffusion interference microscopy, is presented and pertinent results obtained by this technique are reported.

Abstract The sections in this article are Introduction Concepts of Acidity and Basicity of Zeolite and Oxide Catalysts Analysis of Acidity and Basicity Conclusion

AbstractThe sections in this article areIntroductionComparison of Conventional and Solid‐State Ion ExchangeExperimental Procedure for Solid‐State Ion Exchange in ZeolitesMethods of Monitoring Solid‐State Ion ExchangeInfrared SpectroscopyESRSpectroscopyMössbauer SpectroscopySolid‐StateNMRSpectroscopyX‐Ray DiffractionExtendedX‐Ray Absorption Fine Structure (EXAFS) andX‐Ray Absorption Near Edge Structure (XANES)Temperature‐Programmed Evolution (TPE) of Volatile GasesThermogravimetric Analysis (TGA)Systems Investigated for Solid‐State Ion Exchange in ZeolitesSolid‐State Ion Exchange with Salts of Alkaline MetalsSolid‐State Ion Exchange with Salts of Alkaline Earth MetalsSolid‐State Ion Exchange with Salts of LanthanumSolid‐State Ion Exchange with Salts of CopperSolid‐State Ion Exchange with Salts of IronSolid‐State Ion Exchange with Salts of ManganeseSolid‐State Ion Exchange with Salts of Noble MetalsMiscellaneousSome Considerations on Thermodynamic and Kinetic Aspects ofSSIEEffect of Temperature and Salt Concentration in Salt/Zeolite MixturesThe Role of Water in Solid‐State Ion ExchangeKinetics of Solid‐State Ion ExchangeA Possible Mechanism of Solid‐State Ion ExchangeModified Solid‐State Ion Exchange and Related ProcessesContact‐Induced Ion ExchangeIncipient Wetness Technique of ImpregnationGas‐Phase‐Mediated Processes Related to Solid‐State Ion ExchangeOxidative and Reductive Solid‐State Ion ExchangeA Tabulated Survey of the Systems Studied inSSIEand Related ProcessesConcluding Remarks

"Molecular Sieves - Science and Technology" covers, in a comprehensive manner, the science and technology of zeolites and all related microporous and mesoporous materials. Authored by renowned experts

The basic principles of a Fourier Transform IR (FTIR) method are introduced for measurements of diffusivities (D(0)) in single-component diffusion, co- and counter-diffusion (in the case of binary mixtures) and related data (activation energy of diffusion, E,, heat of adsorption, Q) of systems with microporous sorbents. As microporous sorbents H-ZSM-5, H-mordenite, H,Na-ZSM-5, silicalite, Li-ZSM-5 and Na-ZSM-5 are employed. Adsorbates studied are benzene, ethylbenzene, p-xylene and pyridine. It is shown how the reliability of the FTIR method was checked and confirmed via comparison of the FTIR results derived for the system benzene/H-ZSM-5 with the large body of literature data reported for the same system but obtained with various independent techniques. Similarly, the FTIR results of the other systems are discussed in view of literature data, if available. In comparison to single-component diffusion, it is generally found via the FTIR method that the diffusivities in co- and counter-diffusion are lower by about 50%. It is observed that, in H-ZSM-5, D(0)(p-xylene) > D(0)(benzene), a result which is not a priori expected. The investigation of pyridine diffusion in H-mordenite and H-ZSM-5 was hampered by the strong interaction of the base with the Bronsted acid sites of the zeolite and the upper limitation of the temperature of the experiment (575 K); it could be studied, however, in the absence of strong acid sites, e.g. in the systems pyridine/silicalite or pyridine/Li-ZSM-5 and pyridine/Na-ZSM-5. (c) 2005 Academie des sciences. Published by Elsevier SAS. All rights reserved.

ChemInformVolume 33, Issue 40 p. 243-243 Reviews Solid-State Ion Exchange in Microporous and Mesoporous Materials. Hellmut G. Karge, Hellmut G. Karge Fritz Haber Inst., Max-Planck-Ges., D-14195 Berlin, GermanySearch for more papers by this authorHermann K. Beyer, Hermann K. Beyer Fritz Haber Inst., Max-Planck-Ges., D-14195 Berlin, GermanySearch for more papers by this author Hellmut G. Karge, Hellmut G. Karge Fritz Haber Inst., Max-Planck-Ges., D-14195 Berlin, GermanySearch for more papers by this authorHermann K. Beyer, Hermann K. Beyer Fritz Haber Inst., Max-Planck-Ges., D-14195 Berlin, GermanySearch for more papers by this author First published: 19 May 2010 https://doi.org/10.1002/chin.200240243AboutPDF 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. Volume33, Issue40October 8, 2002Pages 243-243 RelatedInformation

A number of techniques and methods suitable for investigation of coke formation on acidic zeolite catalysts is presented and their application illustrated by pertinent results. Such tools for studying coked zeolite catalysts are: various spectroscopic techniques (IR, NMR, ESR, UV-VIS); gravimetry (TGA, also combined with GC and MS) for the determination of the amount of coke deposits and their H/C ratio; extraction of the coked zeolite and chemical analysis (GC, MS) of the extracts; adsorption measurements. Particular attention is paid to the problem of the nature of coke components and, in this context, some emphasis is laid on the distinction between different types of coke. Important phenomena related to coke lay-down such as the effect of acidity, shape selectivity, mechanism and kinetics and location of coke deposition are also discussed.

Lanthanum-exchanged zeolites X, Y, and EMT, containing either sodium or potassium as residual cations, were used as catalysts in two acid-catalyzed hydrocarbon reactions, viz. the disproportionation of ethylbenzene and the isomerization of n-octane (for the latter reaction, Pd/γ-Al2O3 was admixed to the acid zeolites to make the catalysts bifunctional). All pairs of LaM-type zeolites (where M stands for Na or K) showed remarkable activity differences, the LaK form being always less active than the LaNa form. IR and 1H NMR spectroscopy revealed that, for a given zeolite type and degree of lanthanum exchange, the concentration of bridging hydroxyl groups in the large cages was at least 20% lower than that for the LaK form. 139La NMR spectroscopy indicated that the concentration of lanthanum ions in the large cages of the as-exchanged LaK forms was always lower than that in the corresponding LaNa forms. Surprisingly, already in the as-exchanged LaK forms, some La3+ migration into the small cages appears to occur, and this was corroborated by framework strains indicated by 29Si and 27Al NMR. It is proposed that potassium cations in the large cages cause an enhanced migration of lanthanum cations into the small cages and a preferential formation of Brønsted acid sites in these small cages during the thermal dehydration of lanthanum cations (Hirschler–Plank mechanism). A similar effect was found in HNaY and HKY zeolites: The presence of the bulkier potassium cations causes a significant diminution of the accessible Brønsted acid sites in the large cages and of the catalytic activity. Overall, one must conclude from these results that in zeolites possessing both large and small cages, the nature of the residual alkali cations can exert a pronounced influence on the local distribution of the Brønsted acid sites, regardless of how these sites were generated. Copyri ght 2001 Academic Press.

This chapter explores the use of infrared (IR) spectroscopy for characterization of vibration frameworks in zeolites. IR spectroscopy of self-supporting wafers and diffusive reflectance IR Fourier transform (DRIFT) spectroscopy of zeolite powders enable the investigation of cation vibrations in the far IR region. They are also used to employ heat treatment, to achieve complete dehydration and, if desirable, to admit probes. Also, the (thermal) stability of zeolitic materials against, for example, dehydration, dehydroxylation and interaction with sorbates, may be characterized by (in situ) transmission IR or DRIFT. In the far infrared region (200 - 50 cm-1) vibrations of cations against the framework occur. The wave number of the corresponding IR bands depends on the nature of the cations as well as on their siting. Extra-framework species such as aluminium-containing entities, which occur upon dehydroxylation, may be detected and quantitatively determined by IR spectroscopy when suitable probe molecules are employed as adsorbates. Hydroxyl groups attached to zeolite structures may be detected and characterized by IR spectroscopy as such due to their vibration modes or with the help of probe molecules. Investigation of the overtone and combination vibrations of hydroxyls via DRIFT spectroscopy is a valuable means for characterization of zeolite materials since it frequently reveals more detailed features than are obtained from the fundamental stretch region.

Earlier kinetic investigations of ethylbenzene disproportionation over medium-pore zeolite catalysts revealed that the para selectivity for the diethylbenzenes produced increases strongly with crystal size. Two models for diethylbenzene isomerization have been offered as a possible explanation for the observed dependence: secondary isomerization on the external surface of the zeolite crystallites (I) and isomerization inside the zeolite pores combined with faster diffusion of para-diethylbenzene (II). The present paper describes additional investigations, aimed at obtaining evidence for one of these models. Thus, in a series of catalytic experiments the effect of the deactivation of the outer crystallite surface of H-ZSM-5 samples on the distribution of the diethylbenzene product was examined. Further, sorption of pure para-, meta-, and ortho-diethylbenzene from the gas phase over H-ZSM-5 was studied by means of in situ infrared spectroscopy. Both types of investigations provided evidence that diethylbenzene isomerization occurs in the interior of H-ZSM-5. Thus, the para-selective features of H-ZSM-5 reflect the interplay of catalytic reaction and mass transfer phenomena. It was additionally shown that para-diethylbenzene and meta-diethylbenzene are reversibly sorbed in H-ZSM-5 in contrast to the ortho isomer, which cannot enter the zeolite pore system in the temperature range examined (359–522 K).

The conversion of isopropanol in a fixed bed flow reactor was used as a test reaction for a number of faujasite-type zeolites which were modified in order to increase their basicity. Samples included a CsY zeolite with an intact faujasite structure and an exchange degree of nearly 100% prepared by solid-state ion exchange, a CsNaY obtained from CsY through exchange with aqueous NaCl solution, a CsNaX obtained from NaX and aqueous CsCl solution, and a Na(Ge)X, with Si replaced by Ge. At 623 K, an isopropanol partial pressure of 5 kPa in He, and a total feed flow of 90 ml/min, a catalyst mass of 50 mg, initial yields were as follows: NaY: 62% propene, CsNaY: 78% propene, NaCsX: 10% propene, 0.37% acetone, Na(Ge)X: 8% propene, 11% acetone. Conversion in the presence of CsY was <1%. CO2 adsorption and infrared (IR) spectroscopy were used to probe basicity, and Na(Ge)X was the only sample to form monodentate carbonates upon CO2 adsorption (bands at 1477 and 1428 cm−1). Further characterization with X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal analysis, nitrogen sorption, and isopropanol sorption was necessary to properly interpret catalytic results by identifying samples which contained impurities, had blocked pore systems, or decomposed partially during activation or reaction.

A sodium ilerite, molar ratios 1Na2O:8.2SiO2:10.2H2O, was obtained with a good crystalline structure and characterized by several NMR techniques in addition to X-ray diffraction (XRD). The X-ray pattern of the as-synthesized ilerite is in very good agreement with the structure proposed by Gies and coworkers. The narrow 29Si MAS NMR signals (FWHM=0.3 ppm) indicate a good short-range order of the framework. The proton dynamics influences several 29Si NMR parameters. The 16 ppm signal in the 1H MAS NMR spectra is explained by a proton in a bridging position in the short (2.3 Å) O4–O4 bonding. The quadrupole coupling constant Cqcc=100 kHz with η=0.2 for the 16 ppm signal, which was obtained from the 2H MAS NMR spectra, confirms this explanation. 17O NMR shows also a separate signal for SiOH groups but cannot resolve the three expected lines for SiOSi. PFG NMR detects a small mobile portion of water in the ilerite, which is located probably on the external surface of the crystallites. An intracrystalline diffusion coefficient of the intercalated water molecules of the order of magnitude 10−15 m2s−1 was obtained by NMR tracer exchange experiments.

In this contribution the relationship between the reaction kinetics of the disproportionation of ethylbenzene and the pore structure of the zeolite catalyst is discussed. Earlier studies of the kinetics revealed that over large-pore zeolites at low temperatures the reaction rate is significantly but reversibly retarded by the product diethylbenzene. In contrast, with medium-pore zeolites no product inhibition was observed. As a possible explanation it was suggested that the difference between the adsorption constant of the inhibiting product and that of the feed is more strongly pronounced in large- than in medium-pore zeolites. This proposal is supported by some further dissimilarities in the catalytic behavior of these zeolites. Thus, both the evaluation of the deficit of the product diethylbenzene compared with the product benzene during the induction period of the reaction, and transient experiments, in which the feed flow rate was suddenly changed, indicate a stronger accumulation of the diethylbenzene in faujasite than in H-ZSM-5. In agreement with these results different reaction networks for the dealkylation of ethylbenzene and diethylbenzene over large- and medium-pore zeolites were observed at higher temperatures. Sorption measurements with pure ethylbenzene and diethylbenzene on H-ZSM-5 and Y-zeolites confirmed the assumption that with decreasing pore-size the product is no longer sorbed more strongly in the zeolite than the feed.

In this study, we present the first systematic investigation of the adsorption of n-propylbenzene, isopropylbenzene, and n-butylbenzene in H-ZSM-5. Both the sorption isotherms and the rate of sorption uptake were investigated at temperatures between 315 and 425 K. The adsorption isotherms are of type I and are reasonably well described by the Langmuir-Freundlich model. It is shown that the heat of adsorption of the longer sorbate molecules depends significantly on the concentration, thus indicating an increased influence of sorbate-sorbate interaction. The uptake rates are determined by Fickian diffusion. The activation energies for the diffusion process are identical for all systems (32-36 kJ/mol). The diffusivities are also in the same order of magnitude decreasing noticeably for sorbates with longer or more complex substituents. A tentative explanation based on a simple jump-rate model for intracrystalline diffusion is given.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.