X-type Zeolite Research Articles

Alkylation of toluene with methanol on commercial X zeolite in different alkali cation forms

Catalytic alkylation of toluene with methanol was studied at atmospheric pressure, 698 K, and toluene/methanol = 5 mol/mol in a fixed bed reactor. Catalysts were prepared from the Na form of a commercial, pelleted X-type zeolite by ion exchange with alkali cations. Selectivity for side-chain alkylation increased when alkali hydroxide solution instead of alkali salts was used for ion exchange. High selectivity for ethylbenzene formation was achieved on zeolites in the K or Cs form containing excess alkali hydroxides. The turnover number in side-chain alkylation increases with the decreasing amount of strongly adsorbed pyridine or acetic acid per cation.

Influence of weakly coordinated cations and basic sites upon the reaction of H 2S and CO 2 on zeolites

Batch formation of COS and H 2O by heterogeneous reaction of H 2S and CO 2 on A- and X-type zeolites with various degrees of alkaline earth cation-exchange, on faujasite-type zeolites with various Si Al ratios, and on alkaline cation-exchanged X-type zeolites, has been studied. Results obtained at different reaction times illustrate the dual function of the zeolites as selective sorbents causing a shift in reaction equilibrium and as catalysts. Correlations between the catalytic activity and population of cation sites with low oxygen coordination have been found. Furthermore, the catalytic activity could be correlated with the efficiency of dissociative H 2S adsorption (literature data) and the basicity of zeolites. These correlations are regarded as being in accordance with the concept of basic catalysis on zeolites.

Catalysis of organic reactions by molecular sieve systems: 1. Meerwein-Ponndorf-Verley reductions

n-C 5 – C 12 alkanals underwent highly selective (9̆9% at 100 °C) Meerwein-Ponndorf-Verley (MPV) reduction in a continuous flow reactor, by applying as reducing agent a two-component hydrogen-transfer system consisting of NaX-type zeolite and isopropanol. Citronellal (1), which contains a Δ 6,7 double bond, underwent with MX-isopropanol systems (where M = alkali or alkaline-earth cation) two competing reactions, i.e., cyclization to isopulegol (2) or normal MPV reduction to citronellol (3). The direction of the reaction can be fully controlled by the type of exchangeable metallic ion in the X-type zeolite, CsX, yielding the MPV reduction product 3 with a selectivity of 92.3% at 150 °C, while LiX, NaX and CaX preferentially produce the cyclic compound 2. Non-substituted and alkyl-substituted cycloalkanones, having 4- to 15-membered rings were also investigated. The relative MPV conversions to the corresponding cycloalkanols at 100 °C and 180 °C were found to depend on the size of the ring system and, for substituted cycloalkanones, on the position and size of the alkyl substituent. Steric effects due to the geometry of the zeolite intracrystalline channel were also indicated. A limit in the applicability of the MPV reaction was reached with cyclopentadecanone, which was resistant to reduction. A mechanistic scheme for the zeolite-catalyzed MPV reductions is proposed.

Beiträge zur kinetik der zeolith-dehydratation

The values of activation energy and order of reaction characteristics of dehydration of synthetic (A-type zeolite) and natural phillipsite and synthetic faujasite (X-type zeolite) have been determined from the derivatographic curves by the modified method of Freeman and Carroll. There is an agreement between the real and apparent reaction kinetics data and bond relation of zeolitic waters.

UV-visible transmission microscope spectrophotometry on X-type zeolites: Part II. Motion of benzene and toluene within zeolite cavities

Comparative UV spectroscopic investigations on benzene- and toluene-loaded zeolite NaX and NiNaX single crystals were carried out. Absorption spectra of both aromatic compounds in different environments were obtained employing the method of microcomputer-controlled microscope spectrophotometry (MMSP) and of microcomputer-driven photon counting for spectroscopy (MPS). Additional high resolution spectra showed a rotational fine structure superimposed on single vibronic bands of benzene and toluene. A quantum theoretical analysis of the spectra indicates the formation of Na +- and Ni 2+-aryl complexes, but a stronger interaction between the aromatic system and the zeolite lattice in the case of NiNaX zeolites.

The influence of the size and concentration of alkaline earth ions on the structural and sorption properties of faujasites

The structural and sorption properties of type X and Y zeolites, ion-exchanged with Mg 2+, Ca 2+, Sr 2+, and Ba 2+ ions have been studied by X rays, IR, and adsorption. The nitrogen sorption in the zeolites was found to decrease with increased alkaline earth content in both X and Y zeolites and followed a general sequence Na + > Mg 2+ > Ca 2+ > Sr 2+ > Ba 2+. A similar trend was shown for the sorption of water, ethanol, and benzene vapors. Equilibrium sorption capacity and diffusion coefficient decreases with increase in cation radius. The sorption behavior of 1:3:5 trimethylbenzene (TMB) was specific: in X-type zeolites the substitution of Ca 2+ or Ba 2+ ions revealed a sharp fall in the sorption of 1:3:5 TMB, which is attributed to a blocking effect caused by Ca 2+ or Ba 2+ cations in the windows (SI site) large cavities.

Far-infrared studies on zeolites

The far-infrared spectra of X-type zeolites were measured. In the far-infrared region vibration bands occur, which are sensitive to exchangeable cations. The behaviour of these cation vibration bands upon adsorption of H 2O, H 2S, C 6H 6 and other molecules is analysed. While the bands assigned to SIII cation vibrations vanish with increasing amount of adsorbed molecules, the bands assigned to SII cation vibrations shift to lower frequencies and low and high frequency shoulders appear if adsorption takes place.

Dimerization of olefins with nickel-surface complexes in X-type zeolite or on silica

EPR spectroscopy shows that monomeric paramagnetic Ni(I) species, dispersed in X-type zeolite or on SiO2, can reversibly bind ligands (L) such as CO, C2H4 and C3H6 to lead to various Ni(L)+n species, depending on the pressure. Under low pressure (<40 torr), tetrahedral Ni(L)+ and square planar Ni(L)+2 entities are obtained. At higher pressure, Ni(I) has a trigonal bipyramid structure and forms Ni(L)+3 and Ni(L)+4 complexes. This stereochemistry implies in each case a given number of surface O2−s acting as ligand. The 17- and 19-electron Ni(I) complexes easily undergo monosubstitution reactions in their coordination sphere, while addition reactions are observed for 17-electron complexes. At 298 K the supported Ni(I) ions are active and selective for ethylene and propylene dimerization. After a pretreatment at 973 K, the silica-supported catalyst leads to trimerization together with dimerization. Via poisoning experiments, it is shown that the case of two olefin molecules bonded to each Ni(I) favours dimerization.

Structural changes of faujasite—Type zeolites under the influence of sulfur dioxide adsorption

The X-ray and IR studies of faujasite-type zeolites after sulfur dioxide adsorption showed that in the case of X-type zeolites a partial destruction of the zeolite lattice occurred. The modified X-type zeolites have smaller resistance to the SO2 treatment. No influence of sulfur dioxide on the structure of Y-type zeolites was observed.

Influence of the Claus reaction on the structure of faujasite-type zeolites

Infrared spectra in the structural region and X-ray investigations indicate that during the Claus reaction on X-type zeolites partial dealumination of the crystal structure occurs. The dealumination is smaller at 453 K than at 343 K. This type of dealumination has not been observed on Y-type zeolites.

Changes of activity and selectivity of MgNaX zeolites for butene isomerization enhanced by nitrogen dioxide adsorption

Enhancement of butene isomerization on Mg-exchanged X-type zeolites by the adsorption of nitrogen dioxide was investigated by means of kinetics and ir spectroscopy. The catalytic activity of the zeolites for the double-bond migration of butenes was increased when the amount of adsorbed NO 2 was enlarged. The selectivity of the cis-trans isomerization of 2-butenes exceeded their double-bond migration when the amount of adsorbed NO 2 was increased. These phenomena have been explained in terms of intensification of the acid strength of an acidic hydroxyl group on the zeolites by adsorbed NO 2. The formation of nitrato complexes, identified by the observation of ir spectra of the zeolites, was related to the intensification.

Dielectric and far-infrared investigation of cation movements in X-type zeolites. Study of their correlations

A study is reported of the correlations between the movements of cations in partially rubidium-exchanged X zeolites. The study shows that electrostatic repulsions between the cations have no influence on the mechanism responsible for the correlations observed with dielectric relaxation. Moreover, by using far-infrared spectroscopy it is possible to infer that these repulsions are weak compared with the cation–framework interactions.

Reactions of dimethylbutenes on nickel-exchanged and zinc-exchanged 13X-type zeolites

Reactions involving 2,2-dimethylbut-l-ene (I), 2,3-dimethylbut-l-ene (II) and 2,3-dimethylbut-2-ene (III), including isomerization and exchange with D2 or D2O, have been studied on zinc-exchanged and nickel-exchanged X-type zeolites. The effect of various pretreatments (with hydrogen, carbon monoxide or oxygen) was examined with NiX (21% exchanged) which, unlike the ZnX zeolites, was a catalyst for the hydrogenation of the C6 alkenes.

UV-visible transmission microscope spectrophotometry on x-type zeolites: Part I. Formation of different nickel complexes in zeolite X

Comparative UV-visible spectroscopic investigations on single crystals of nickel(II) salts of D 4h symmetry and of NiNaX zeolites with various nickel contents were carried out. The transmission spectra were recorded by means of a microcomputer-controlled microscope spectrophotometer (MMSP method). The absorption curves of NiNaX zeolites showed different symmetries of nickel(II) complexes within zeolites depending on the degree of ion exchange. An absorption maximum of 260 nm characteristic for nickel(II) complexes of D 4h symmetry was detected only at low degrees of ion exchange, whereas the spectra of highly-exchanged NiNaX zeolites were almost identical to those of octahedral nickel complexes obtained from aqueous solutions of nickel(II) salts. The formation of differently coordinated nickel complexes is discussed in terms of graph theory, assuming various molecular complexes whose graphs represent all relations between the cations and the surrounding zeolite lattice.

X-ray study of the reduction and reoxidation of nickel(2+) ion in x-type zeolite in the presence of cerium(3+) ion

X-ray study of the reduction and reoxidation of nickel(2+) ion in x-type zeolite in the presence of cerium(3+) ion

Catalytic activity of the hydroxyl group produced by NO 2 adsorption on Ca-exchanged zeolites

The enhancement of acid catalysis by the adsorption of nitrogen dioxide has been studied on the calcium ion-exchanged X-type zeolites of various degrees of the exchange. The enhancement is ascribed to the formation of the acidic hydroxyl group by the adsorption of nitrogen dioxide. As the ion-exchange degree increases, the formation of the hydroxyl group shows an optimum at 50 ~ 60%, but the catalytic activity for the isomerization of butenes continuously increases with steep acceleration at the exchange degree of 40 ~ 50%. The activity of an acidic hydroxyl group is strongly dependent on the number of calcium ion in the supercage of the zeolite. The formation of nitrate ion and nitrato complex observed by ir spectroscopy on the zeolite has been discussed in relation to the hydroxyl group formation.

Location of Zn2+ ions in Zn-Y zeolites and the SO2-induced activities in the isomerization of cis-but-2-ene

The SO2-induced isomerizations of cis-but-2-ene, the cis-trans conversion and the double-bond shift, have been studied over Zn-Y zeolites as functions of the degree of zinc-exchange of Na-Y zeolite. The location of Zn2+ in the zeolites has been examined by volumetric measurements of CO and CO2 adsorptions and by infrared absorption measurement of CO adsorption. The Zn2+ introduced may locate preferentially in the small cages (the prisms and the sodalite cages) for zeolites with degree of exchange less than ca. 60%. Above this level of exchange the divalent cations can locate in the supercages. These characteristic locations of Zn2+ have also been reported for the X-type zeolites. The Zn2+ in the supercages are the most effective for causing the SO2-induced cis–trans isomerization for both the X- and Y-type zeolites. The Zn2+ located in the small cages of Y zeolites can both initiate the SO2-induced cis–trans isomerization and generate the Bronsted acid sites necessary for the carbenium ion type isomerization. However, the Zn2+ in the small cages of X zeolites did not show such ability. The different results observed between the X-and Y-type zeolites have been ascribed to the difference in the distributions of SiO4–4 and AlO5–4 in the six-membered rings for the two types of zeolite.

Enhancement of catalytic activity of calcium X-type zeolite by preadsorption of nitrogen dioxide

The ability of preadsorbed nitrogen dioxide to induce the isomerization of butenes on calcium-ion-exchanged X-type zeolite catalyst has been studied by kinetics and ir absorption spectroscopy. The induced catalytic activity for the reaction increases linearly with increasing amounts of adsorbed nitrogen dioxide. The formation of zeolitic, acidic hydroxyl groups on the adsorption of nitrogen dioxide is proportional to the amount of adsorbed nitrogen dioxide as has been demonstrated with ir absorption spectra of the catalyst. The induced catalytic activity is ascribed to catalysis by this newly formed, acidic hydroxyl group.

Location and reducibility of nickel(2+) ions in an X-type zeolite in the presence of lanthanum(3+)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLocation and reducibility of nickel(2+) ions in an X-type zeolite in the presence of lanthanum(3+)M. Briend-Faure, J. Jeanjean, D. Delafosse, and P. GallezotCite this: J. Phys. Chem. 1980, 84, 8, 875–878Publication Date (Print):April 1, 1980Publication History Published online1 May 2002Published inissue 1 April 1980https://doi.org/10.1021/j100445a017RIGHTS & PERMISSIONSArticle Views56Altmetric-Citations32LEARN 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 (584 KB) Supporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Stabilized Y-type zeolites for gas chromatographic separation

A partially decationized Y zeolite was pretreated under specific conditions. It was found that this calcinated zeolite retains its separation properties for mixtures of the gases H 2, O 2, N 2, CH 4 and CO but has much lower affinity for water molecules than untreated, e.g., A- or X-type zeolites. The observed effect is discussed on the basis of the results of adsorption measurements (adsorption isotherms, capacities, heats of adsorption).