G. Pál-Borbély

Synthesis and characterization of a ferrierite made by recrystallization of an aluminium-containing hydrated magadiite

Abstract A new method for the synthesis of high-silica ferrierite (Si/Al=15–18) by recrystallization of aluminium-containing magadiite varieties in air-dry state and aqueous suspension with piperidine as template is reported. Details on removal and thermal stability of the template occluded during the synthesis (four molecules per unit cell) are given. Properties (e.g. thermal and hydrothermal stability, acidity) of ferrierites prepared by the dry synthesis technique are presented and compositional and morphological characteristics of the products are compared with those of ferrierite conventionally prepared from alkaline SiO 2 /Al 2 O 3 gel in aqueous medium.

Cyclohexane conversion over H-zeolite supported platinum

The catalytic conversion of cyclohexane over H-ZSM-5 in hydrogen or nitrogen and in hydrogen atmosphere over a series of H-zeolites loaded with platinum was studied using a flow-through microreactor/GC on-line system at pressures of 13 bar. The distribution of the products formed via hydrodecyclization was found to depend definitely on whether or not dimerization of primarily formed hexyl-carbenium ions is sterically hindered in the zeolitic pore system. Reaction routes are suggested which involve, as an essential step, the hydrogenation of intermediate carbenium ions, formed either primarily by reactant adsorption or cracking, by spill-over hydrogen activated on the metallic catalyst component. The basically different product distribution obtained by decyclization of cyclohexane in nitrogen atmosphere or over monofunctional H-ZSM-5 is attributed to disproportionation of primarily formed hexyl-carbenium ions and subsequent hydrogen transfer reactions which results in a broad spectrum of paraffins and aromatics in the effluent and in carbon-rich deposits on the catalyst surface causing fast catalyst deactivation. This process does not manifest itself in bifunctional catalysis due to the much faster hydrogenation and, hence, elimination of carbenium ions by hydrogenation.

Recrystallization of magadiite varieties isomorphically substituted with aluminum to MFI and MEL zeolites

Abstract Magadiite varieties isomorphically substituted with aluminum and their aluminosilicic acid derivatives retaining the framework topology of magadiite are recrystallized, after incorporation by ion exchange of four TPA and TBA ions, to MFI- and MEL-type zeolites, respectively. The recrystallization degree and the size and shape of the zeolite crystallites formed can be controlled by the amount of template applied. Partial recrystallization results in products which promise to be advantageously applicable as catalysts because of the small crystallite size of the zeolitic component.

Solid-state ion exchange in zeolites. Part 5.—NH4-Y–iron(II) chloride

Solid-state ion-exchange reactions proceeding upon grinding of hydrated NH4-Y zeolite and FeCl2·4H2O in air and subsequent heating in vacuum have been followed by X-ray diffraction (XRD) and temperature-programmed evolution of volatile reaction products (H2O, NH3 and HCl) monitored by mass spectrometry (MS). Changes in valence state and coordination environment of the exchanged iron ions upon heat treatment up to 720 K in vacuum and air, as well as in hydrogen after treatment in air, were studied by Mossbauer spectroscopy. Partial ion exchange and oxidation to cationic hydroxy-iron(III) species proceed upon mere grinding. Heat treatment in vacuum results in partial autoreduction and characteristic environmental changes of di- and tri-valent Fe species, especially in the temperature range between 620 and 720 K. In an oxidizing atmosphere, autoreduction is suppressed; however, at temperatures >520 K, iron(III) oxide is formed in increasing amounts. Reduction by hydrogen subsequent to heat treatment in air at 720 K results in the formation of a magnetite-like oxide phase and some metallic α-iron.

Transalkylation of toluene with cumene over zeolites Y dealuminated in solid-state: Part II. Effect of the introduced Lewis acid sites

The effects of the introduced Lewis acid sites of different kind (InO+ or AlO+) and the variation of InO+ concentration on the catalytic behavior of dealuminated in solid-state HY zeolites in the reaction of cumene–toluene transalkylation have been studied. The catalysts, indium modified HY(3.7) and ultra stable zeolite USY(3.4), containing essentially equivalent amounts of framework aluminum and Lewis acid sites (InO+ and AlO+, respectively), have been compared to the initial HY(3.7), not containing any extra-framework aluminum (EFAl). Strictly controlled conditions were used for the formation of Lewis acid sites: through reductive solid-state ion exchange (RSSIE) for InO+ or by steaming in the case of AlO+. The ratio between the Lewis and Broensted acid sites was varied by progressive replacement of the protons by InO+ cations in HY(5.6) zeolite. The zeolites modified by monovalent (InO+ and AlO+) have, as a result, an enhanced catalytic activity in comparison with HY(3.7). This effect is mainly due to intense side reactions of dealkylation, oligomerization, cracking and re-alkylation at the expense of the cymenes formation. The data for the distribution of the reaction products suggest a highly preferred mechanism of dealkylation/alkylation with the increase of the Lewis/Broensted acid site ratio. The presence of cation-connected Lewis acid sites is supposed to be responsible for the fast samples’ deactivation.

Comparison of the Redox Properties of Iron Incorporated in Different Amounts into MCM-41

Mesoporous Fe-MCM-41 samples with different framework iron contents were tested as catalysts in CO oxidation and characterized by TPR,Mössbauer and FTIR spectroscopies after heat treatment in high vacuum and reductive or oxidative atmospheres. In samples with Si/Fe ratiosof 20 and 12 all of the iron was found to be reducible with H2, but only a part of Fe(III) species could be reduced to Fe(II) in materialswith lower iron content. In neither of the materials could Fe(III) be fully converted with CO to the divalent oxidation state. A significant part ofiron can be reversibly reduced and reoxidized in successive redox cycles. Large Fe-O clusters could not be detected.

Incorporation of cations into zeolites by a new reaction between Brönsted acid zeolites and metals. I. Zinc into faujasites and mordenites

Abstract A redox reaction was found to proceed between metallic zinc and zeolitic lattice protons when ground mixtures of zinc dust ( 4 ,Na–Y zeolite, mordenite or varieties of these zeolites prepared by steaming or acid leaching were heated in a vacuum or an inert atmosphere to temperatures above 250°C. This process results in the evolution of molecular hydrogen and in the formation of Zn 2+ cations occupying, as evidenced by XRD and FTIR spectroscopy, lattice cation sites in the zeolite structure. The reported redox reaction can be regarded as the solid-state analogue of the dissolution of metals in aqueous solutions of acids. In the case of NH 4 ,Na–Y with zinc admixed in an amount equivalent to the ammonium content, the amount of the evolved hydrogen was found to be equivalent to the amount of Bronsted acid sites in the zeolitic component. The hydrogen release proceeded, depending on the type and modification of the applied zeolite, in different temperature ranges. Possibilities of developing a highly sensitive method for the quantification and distinction of hydroxyl groups in zeolites on the basis of the reported reaction are discussed.

Acidity of isomorphically substituted crystalline silicic acids with layer structure. I. H-magadiite

Pure crystalline silicic acid prepared from magadiite does not contain acid sitesdetectable by IR spectroscopic methods, ammonia TPD and adsorption heat measurements. Isomorphic substitution of silicon by aluminum or gallium in the framework of magadiite creates strong Bronsted-acid sites. Part of the incorporated aluminum, released upon heat treatment from the framework of ammonium-exchanged magadiite, occupies cationic lattice sites and forms strong Lewis sites. Ion exchange with hydrochloric acid results in extraction of a considerable part of the framework Al by acid leaching. Incorporation of Ga into the crystal sheets of magadiite results in materials with stronger Bronsted- and Lewis-type acid sites than that found in the respective aluminum varieties. Ga containing silicic acid with magadiite structure proved to be also more resistent to heat treatments and acid leaching.

The skeletal isomerization of n-butene over ferrierite catalysts

Abstract The catalytic properties of H-ferrierite zeolites, prepared by hydrothermal and dry-state synthesis, were compared in the skeletal isomerization of 1-butene. The activity was found to be strongly influenced by the presence of extra-framework Al (EFAl) species in the zeolite micropores and by the carbonaceous deposit formed during the reaction. The dynamics of mass transport in the zeolite crystallites were studied by the frequency-response (FR) method using acetylene, propane, n - and i -butane as probe molecules. The selectivity of n -butene conversion showed correlation with the dynamics of the n -butane sorption process. Either the diffusion or the sorption was the rate-controlling slowest step of n -butane mass transport, depending on the amount and the distribution of the EFAl species in the sample. In the catalyst sample, free of EFAl, the transport was found to be controlled by the rate of sorption. At an EFAl content of about 0.5–1.0 EFAl/unit cell the diffusion resistance of the micropores governed the n -butane transport rate.

Dynamic and catalytic studies of H-ferrierites made by hydrothermal and dry state syntheses

Abstract The activity and selectivity of skeletal isomerization of 1-butene and disproportionation of ethylbenzene on H-ferrierite catalysts prepared by dry state recrystallization of magadiite and conventional hydrothermal synthesis from an alkaline SiO2/Al2O3 gel are compared. The isobutene yields of the samples were found to be similar even though the ferrierite crystals had quite different morphologies. Significant differences were observed in the isobutene selectivities which can be correlated with processes occurring inside the crystals. Ammonia, acetylene, methane and propane sorption and intracrystalline diffusion rate-spectra are reported using the frequency-response technique. The sorption properties of the acid sites and the diffusional resistances of the morphologically different ferrierite crystals are compared. It was found that by the dry state synthesis the quality of the ferrierite framework was similar to that obtained by the conventional hydrothermal synthesis. The channels of ferrierite recrystallized from magadiite, however, seem to have fewer barriers and, thus, show better kinetic properties, e.g., faster diffusion of propane and higher selectivity to the formation of isobutene.