Physico-chemical characterization of the high-silica zeolite catalyst SSZ-74 (ref. 1) suggested that it, like the related materials TNU-9 (ref. 2) and IM-5 (ref. 3), has a multidimensional 10-ring channel system. Such pore systems are ideal for many petrochemical applications, and indeed SSZ-74 has been shown to be a good catalyst for a wide variety of reactions. The elucidation of its framework structure, however, proved to be difficult. Comparable problems were encountered with TNU-9 and IM-5, which were synthesized with related structure-directing agents. Their framework structures, which are the two most complex ones known, both have 24 Si atoms in the asymmetric unit, and were finally solved by combining high-resolution powder diffraction data with information derived from high-resolution electron microscopy images. Therefore, a similar approach, using the powder charge-flipping algorithm to combine the two types of data and molecular modelling to help to locate the structure-directing agent, was applied to SSZ-74. This procedure eventually revealed a most unusual 23-Si-atom framework structure (|(C(16)H(34)N(2))(4)&Si(92)(4)O(184)(OH)(8)]) with ordered Si vacancies.
The syntheses, structure solutions, and physicochemical and catalytic characterizations of the novel zeolites SSZ-53 and SSZ-59 are described. SSZ-53 and SSZ-59 were synthesized under hydrothermal conditions with the [1-(4-fluorophenyl)cyclopentylmethyl]trimethyl ammonium cation and 1-[1-(4-chlorophenyl)cyclopentylmethyl]-1-methyl azocanium cation, respectively, as structure-directing agents. The framework topology of SSZ-53 was solved with the FOCUS method, and the structure of SSZ-59 was determined by model building. Rietveld refinement of synchrotron X-ray powder diffraction data confirms each proposed model. SSZ-53 and SSZ-59 each possess a one-dimensional channel system delimited by 14-membered rings. Results from transmission electron microscopy, electron diffraction, catalytic experiments (spaciousness index and constraint index tests), and argon and hydrocarbon adsorption experiments are consistent with the proposed structures.
The framework structures of two closely related molecular sieves, SSZ-26 and SSZ-33, are described. These materials possess a previously missing but desired structural feature in a group of industrially significant zeolites. They contain a three-dimensional pore system that provides access to the crystal interior through both 10- and 12-rings. This property is a consequence of the organic structure-directing agents used in the synthesis of these materials. These materials are examples of the purposeful design of a micropore architecture. Both SSZ-26 and SSZ-33 contain the 4=4-1 building unit that had been previously found only in natural zeolites.
A model for the structure of the zeolite SSZ-31 is presented.
The model is obtained by combining
information from adsorption capacity measurements, transmission
electron microscopy, and high-resolution X-ray
diffraction. SSZ-31 is a one-dimensional large-pore zeolite with a
framework density of 18.7 tetrahedral(T)-atoms
per nm-3 and a bulk density of 1.87 g
cm-3. The pore apertures are elliptical
with major and minor axes of
approximately 8.6 Å × 5.7 Å. SSZ-31 is an extreme example of a
complex and highly faulted zeolite. The structure
can be described as an intergrowth of four different but structurally
related polymorphs.
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