Journal Article•
The framework topology of zeolite beta
01 Sep 1988-Preprints-American Chemical Society Division of Petroleum Chemistry (American Chemical Society)-Vol. 33, Iss: 4
TL;DR: The tetrahedral framework structure of zeolite beta is disordered along (001) planes as mentioned in this paper, and the disordered structure is related by a/3 and/or b/3 displacements on (1) planes to three ordered polytype structures with triclinic, monoclinic and tetragonal symmetry.
Abstract: The tetrahedral framework structure of zeolite beta is disordered along (001). The disordered structure is related by a/3 and/or b/3 displacements on (001) planes to three ordered polytype structures with triclinic, monoclinic, and tetragonal symmetry. Three mutually perpendicular 12-ring channel systems are characteristic of the three ordered polytypes and the disordered beta structure. The proposed framework structures are consistent with the known diffraction, sorption an cation exchange properties of zeolite beta.
Citations
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TL;DR: A series of mesoporous molecular sieves are synthesized that possess crystalline microporous walls with zeolitelike frameworks, extending the application of zeolites to the mesoporus range of 2 to 50 nanometers.
Abstract: Crystalline mesoporous molecular sieves have long been sought as solid acid catalysts for organic reactions involving large molecules. We synthesized a series of mesoporous molecular sieves that possess crystalline microporous walls with zeolitelike frameworks, extending the application of zeolites to the mesoporous range of 2 to 50 nanometers. Hexagonally ordered or disordered mesopores are generated by surfactant aggregates, whereas multiple cationic moieties in the surfactant head groups direct the crystallization of microporous aluminosilicate frameworks. The wall thicknesses, framework topologies, and mesopore sizes can be controlled with different surfactants. The molecular sieves are highly active as catalysts for various acid-catalyzed reactions of bulky molecular substrates, compared with conventional zeolites and ordered mesoporous amorphous materials.
728 citations
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TL;DR: The presence of basic centers in some oxides has been recognized for a long time as being important in catalysis as mentioned in this paper, and usually both basic and acid sites exist simultaneously, either independently or in a concerted way.
Abstract: The presence of basic centers in some oxides has been recognized for a long time as being important in catalysis [1-4]. Usually both basic and acid sites exist simultaneously. The two centers may work independently or in a concerted way. For instance, in alcohol transformation, dehydration is favored on acidic sites and dehydrogenation on basic centers [3,5]. A large variety of materials are cited as having basic character. They include single-metal oxides (MgO, CaO, ZnO), supported alkali metals (Na/MgO, K/K2CO3), mixed-metal oxides (MgO-A12O3, ZnO-SiO2, MgO-TiO2), zeolites (X and Y saturated with alkaline cations of low electronegativity), hydrotalcite-type anionic clays, asbestoslike materials, carbon-supported basic catalysts, and basic organic resins. ∗ Present address: 16 rue Francois Gillet, 69003 Lyon, France.
451 citations
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TL;DR: In this article, a thorough characterization of zeolite Beta materials with crystal sizes in the 200 to 10nm range has been done by using a combination of physicochemical techniques (N 2 adsorption, XRD, multinuclear MAS NMR, pyridine adaption, FTIR, thermal analysis).
409 citations
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TL;DR: In this article, the modifications of the state of aluminium when introducing protons into zeolite-β have been investigated by combining several analytical techniques, and it was concluded that the octahedrally coordinated and NMR invisible aluminium must be regarded as inherent parts of the framework of the Zeolite and their formation is explained by a distortion of aluminic sites caused by the high electron affinity of the proton.
291 citations
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TL;DR: C confined space synthesis appears to be an attractive method for preparation of zeolites with a controlled size distribution for isolation of the pure and highly crystalline zeolite.
Abstract: Confined space synthesis is a novel method in zeolite synthesis. It involves crystallization of the zeolite inside the pore system of an inert mesoporous matrix. In this way it is possible to prepare nanosized zeolites with a controlled size distribution by proper choice of the inert matrix. Here, confined space synthesis was adopted to prepare nanosized ZSM-5, zeolite Beta, zeolite X, and zeolite A with tailored crystal size distributions using mesoporous carbon blacks as inert matrices. All zeolites were characterized by X-ray powder diffraction, transmission electron microscopy, and nitrogen adsorption/desorption prior to and after removal of the carbon matrix. ZSM-5 with Si/Al ratios of 50, 100, and infinity (silicalite-1) were synthesized with controlled average crystal sizes in the range 20-75 nm. Nanosized zeolite Beta (7-30 nm), zeolite X (22-60 nm), and zeolite A (25-37 nm) were prepared similarly. Removal of the carbon matrix by controlled combustion allows a convenient method for isolation of the pure and highly crystalline zeolites. Therefore, confined space synthesis appears to be an attractive method for preparation of zeolites with a controlled size distribution.
248 citations
References
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TL;DR: Mordenite, a zeolite, was derived by superposition of the three-dimensional Patterson function and partially refined assuming the centric symmetry Cmcm or Cmc2t as discussed by the authors.
Abstract: Mordenite, a zeolite, is orthorhombic with space group Cmcm or Cmc2t. The unit cell of the Na form has dimensions a = 18.13 A, 6 = 20.49 A, c = 7.52 A, and contains Na8Al8Si40O9e · 24H20. Its framework structure was derived by superposition of the three-dimensional Patterson function and partially refined assuming the centric symmetry Cmcm. The aluminosilicate framework of mordenite is composed of a new type of chain, in which 5-membered rings of tetrahedra prevail. Its molecular sieve properties may be attributed to a system of channels, parallel to [001], having a free diameter of 6.6 A, and being interconnected by smaller channels, parallel to * Contribution No. 2690 from the Gates and Crellin Laboratories of Chemistry. 1 Present address: Technikum des Kantons Zürich, Winterthur, Switzerland. 440 W . Μ . M E I E R [010], of 2.8 Ä free diameter. Stacking faults in the framework reduce the effective diameter of the intraerystalline channels to about 4 A. The results of the structure determination suggest an ordered Al, Si distribution reducing the symmetry of the framework to Cmc2i.
299 citations
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TL;DR: In this article, the structure of ZSM-12, a high-silica zeolite, was determined by analysis of electron and X-ray powder diffraction data combined with model building.
140 citations
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TL;DR: ZSM-22 as discussed by the authors, an orthorhombic high silica zeolite (Cmcm, a = 13.86 ± 0.03A, b = 17.41± 0.04A, and c = 5.5 × 4.5 A), has a framework consisting of 5-, 6- and 10-rings.
117 citations
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TL;DR: In this article, a disordered structure consisting of ferrierite sheets linked via bridging oxygens located on mirror planes is proposed for this material, characterized by ten-ring noninterpenetrating linear channels whose ideal dimensions are 5.3 × 5.6 A.
115 citations
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TL;DR: ZSM-23 as discussed by the authors is a high-silica zeolite with lattice parameters of: a = 5.01 ± 0.02A, b = 21.52± 0.04A, and c = 11.13 ± 1.03A.
68 citations