Cesium-exchanged Zeolite Research Articles

Enhancement of the basic properties in FAU zeolites by impregnation with cesium hydroxide

Impregnation of FAU zeolites with seven cesium hydroxide atoms per unit cell improved their basic properties in toluene methylation without affecting the physical properties of the zeolite (framework, silicon/aluminium molar ratio, aluminium coordination, etc.). The enhancement was greater in the zeolites with good initial basic properties such as the cesium-exchanged zeolite. The effect of the impregnation was to first decrease the acid activity and then to increase the basic activity. The basic catalytic activity showed a maximum for a cesium content of 20CsOH/u.c. in the NaX zeolite. Higher contents of cesium hydroxide did not show catalytic activity due to the collapse of the FAU framework. Higher yields of basic methylation were achieved with a zeolite synthesised with occluded alkaline hydroxide (NaKX-I) without post-synthesis treatment. In this case, the cesium hydroxide content yielding the maximum catalytic activity was 15CsOH/u.c.

Raman Spectroscopy and Dioxygen Adsorption on Cs-Loaded Zeolite Catalysts for Butene Isomerization

Cesium-exchanged zeolite X was impregnated with cesium acetate (Cs(Ac)/CsX) or cesium carbonate (Cs(2)CO(3)/CsX) and subsequently calcined to yield a basic catalyst. The Raman spectra of calcined Cs(Ac)/CsX and Cs(2)CO(3)/CsX exhibited a new peak at 1036 cm(-1) associated with the occluded species. No evidence for cesium peroxide or superoxide was observed. The occluded cesium species in both samples is proposed to be an oxycarbonate, which is a metastable intermediate between cesium carbonate and cesium oxide. The isomerization of 1-butene to cis- and trans-2-butene was catalyzed by cesium-loaded zeolite X. Although CO(2) readily poisoned the active base sites for catalysis, pretreatment of a basic zeolite with O(2) at 373 K did not. Co-feeding O(2) with 1-butene at 373 K, however, completely deactivated the base sites. Analysis of the reactor effluent at 473 K and the IR spectrum of the catalyst indicated the formation of carbon dioxide, which irreversibly adsorbed on the basic sites of the catalyst. Deactivation of basic catalysts by O(2) is proposed to occur through a low temperature oxidation of 1-butene to carbon dioxide, which strongly adsorbs on the active sites.

The adsorption and decomposition of cyanogen chloride by modified inorganic molecular sieves

Aluminosilicate and silicate porous solids have been evaluated as supports for triethylenediamine (TEDA) for the adsorption and decomposition of cyanogen chloride. A series of silica-gel supports has been used to study the effect of varying pore size. A series of faujasitic zeolites has been used to examine the effect of the cation exchange capacity of the support and the type of exchangeable cation. Results show that the activity of adsorbed TEDA towards cyanogen chloride appears to increase with increasing support pore diameter, and TEDA seems to be activated by basic adsorption sites on the support. Cesium-exchanged zeolite supports are particularly active. In general, zeolite supports appear to confer significantly higher activity to TEDA than traditional activated carbon supports. A series of mesoporous MCM-41 and AlMCM-41 supports has also been studied, but the activities of adsorbed TEDA are lower than expected. Significantly, the specific surface area of the inorganic supports does not seem to be a primary factor in controlling adsorbed TEDA activity.

Structure/function relationships for basic zeolite catalysts containing occluded alkali species

The basicity and reactivity of alkali-modified zeolites were investigated in order to elucidate the role of occluded species on catalytic activity. To synthesize intrazeolite oxide or metal species, cesium acetate or cesium azide was impregnated into the pores of zeolites and decomposed in situ. To characterize the basicity of the samples, we used adsorption of iodine and carbon dioxide. The blue shift in the UV–visible spectrum of adsorbed iodine was found to increase with increasing electropositivity of the exchangeable cation, indicating greater donor strength of the zeolite framework. Cesium-exchanged zeolite X was an active catalyst for the reaction of ethylene oxide and carbon dioxide to form ethylene carbonate. For a series of faujasite-type zeolites with different loadings of occluded cesium oxide, the CO 2 uptake increased linearly with the amount of occluded Cs. The catalytic activities of the CsO x /CsX samples for the isomerization of 1-butene and dehydrogenation of 2-propanol increased linearly with the amount of excess cesium, consistent with results from the adsorption of CO 2. A majority of the base sites on these materials exhibited a heat of CO 2 adsorption around 85 kJ mol −1, which is much lower than the 270 kJ mol −1 seen on bulk cesium oxide. After thermal pretreatment, Na(azide) and Cs(azide) modified X zeolites catalyzed the side-chain alkylation of toluene with ethylene and the side-chain alkenylation of o-xylene with butadiene, whereas occluded cesium oxide was inactive in the reactions.

Characterization of basic guest compounds on solid catalysts by13C CP/MAS NMR spectroscopy of surface methoxy groups

Silica gel, dealuminated zeolite USY and cesium-exchanged zeolite Y were impregnated with alkali metal hydroxides or acetates followed by calcination. Surface methoxy groups formed upon loading these samples with methyl iodide were applied as 13 C NMR spectroscopic probes to investigate the formation of well dispersed basic guest compounds. The variation of the isotropic 13 C NMR shifts of methoxy groups bound to different guest compounds on silica gel (49.6-48.7 ppm) shows the same tendency as the electronegativities of alkali metal atoms introduced by impregnation. 13 C CP/MAS NMR studies of surface methoxy groups bound to guest compounds on silica gel and zeolites Y revealed an influence of the support on the 13 C chemical shift tensor. The application of this NMR spectroscopic method on cesium-exchanged zeolite Y impregnated with cesium hydroxide allows one to distinguish at least two types of oxidic guest compounds. Copyright © 1999 John Wiley & Sons, Ltd.

Cation Migration in Zeolites: An in Situ Powder Diffraction and MAS NMR Study of the Structure of Zeolite Cs(Na)−Y during Dehydration

In situ synchrotron X-ray powder diffraction and 133Cs and 23Na MAS NMR have been used to investigate the cation migration and ordering in samples of cesium-exchanged zeolite NaY as a function of temperature and cesium cation-exchange level and during dehydration. Samples were prepared with cesium-exchange levels varying from 68 to 83% of the total cation content by carrying out repeated ion-exchange and calcination steps. Lower cesium content samples contain sodium cations in the sodalite cages and cesium cations in the supercages (SII and SIII) directly after the ion-exchange process. After dehydration at 350 °C and above, sodium cations are observed in the supercages (in SII) and in the double 6-rings (SI). A maximum of 8 cesium cations/unit cell (1/sodalite cage) migrate from the super to the sodalite cages, occupying SII‘ and SI‘ positions. The supercage sodium cations are then exchanged for cesium in the subsequent ion-exchange steps, increasing the cesium content. In situ X-ray data, collected duri...

Solid base catalysts for side-chain alkylation of toluene with methanol

A wide variety of solid bases, including alkali-exchanged zeolites X, Y, L and β, and alkali-impregnated carbon and magnesia, were tested as catalysts for the side-chain alkylation of toluene with methanol to form styrene and ethylbenzene. In addition, the effects of adding Group IIIA elements (B, Al, Ga, In) to the catalysts were examined. At 680 K and atmospheric pressure, the major reaction products were styrene, ethylbenzene, and carbon monoxide. Cesium-exchanged zeolite X was the most effective alkali-containing catalyst for the alkylation reaction. Of the Group IIIA additives that were tested, only boron promoted the alkylation reaction. The primary effect of adding boron was to reduce the decomposition of methanol to carbon monoxide. Apparently, boron selectively modifies the sites associated with methanol decomposition without inhibiting the sites active for alkylation. A borated Cs—carbon sample also catalyzed the alkylation reaction, demonstrating that a zeolite framework is not necessary to form the active site. Microporosity seems to play an important role in these catalysts since both the alkali-modified carbons and the zeolites are microporous.

A Quasi-Elastic Neutron Scattering Study of the Ammonium Ions in CsNH4-Y Zeolite

Quasi-elastic neutron scattering has been used to study the reorientation mechanism for ammonium ions in cesium-exchanged zeolite Y. This sample contains ammonium ions preferentially located in the sodalite cages at site 1'. These ions reorientate with 120' or 180' jumps around fixed axes through the nitrogen atom. This corresponds to a bonding geometry in which the ammonium ion interacts via three or two hydrogen atoms with the lattice oxygen atoms. Additionally, a reorientation around a fixed axis through two hydrogen atoms of the ammonium ion may occur. The ammonium ion then jumps between two equilibrium positions: one position involves a 2-fold bonding geometry and the other a 3-fold bonding geometry. At 300 K the effective time interval between two jumps is T = 1.2 f 0.5 ps. Compared to zeolite Rho, the ammonium ions in the cesiumexchanged zeolite Y show a more restricted reorientational behavior, resulting in a larger elastic incoherent structure factor.

Hydrated and dehydrated crystal structures of seven-twelfths cesium-exchanged zeolite A

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHydrated and dehydrated crystal structures of seven-twelfths cesium-exchanged zeolite AT. Blake Vance Jr. and Karl SeffCite this: J. Phys. Chem. 1975, 79, 20, 2163–2167Publication Date (Print):September 1, 1975Publication History Published online1 May 2002Published inissue 1 September 1975https://doi.org/10.1021/j100587a021RIGHTS & PERMISSIONSArticle Views178Altmetric-Citations62LEARN 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 (622 KB) Supporting Info (1)»Supporting Information Supporting Information Get e-Alerts