Ignatius Y. Chan

SSZ-26 and SSZ-33: Two molecular sieves with intersecting 10- and 12-ring pores

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.

Ordered Silicon Vacancies in the Framework Structure of the Zeolite Catalyst SSZ-74

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.

High-resolution electron microscopy characterization of SSZ-25 zeolite

Abstract SSZ-25 has been known to have high catalytic activity, but no structure has been reported. A combination of electron microscopy techniques was employed to characterize this new zeolite. This allowed us to determine the unit cell and its relationship to the crystal morphology. The unit cell was hexagonal with a = 1.41 nm and c = 2.52 nm. The individual crystals tend to be thin flakes, and high-resolution electron microscopy (HREM) revealed that this zeolite has a multi-dimensional channel system. The results of this work showed that there are large-pore zeolite channels arranged parallel to the c direction. The HREM results, when taken with other physical characterization methods, confirmed why this zeolite has high catalytic utility.

A comparative study of three closely related unsolved zeolite structures

Abstract In this report we discuss the synthesis and physicochemical characterizations of three zeolites with unsolved crystal structures: SSZ-57, SSZ-74, and IM-5. The diffraction data of SSZ-57 are similar to, but distinct from, the data for ZSM-5, ZSM-11, or ZSM-5/11 intergrowths. The powder diffraction data of SSZ-74 can be indexed in a unit cell with dimensions similar to those found in ZSM-5 and ZSM-11. The organic structure directing agents (SDA) used to prepare SSZ-74 and IM-5 are similar to SDA molecules that often yield multidimensional 10-ring zeolites. The micropore volumes, adsorption uptake rates of 2,2-dimethylbutane, and the constraint index tests of these three unknown materials are also consistent with those expected for multidimensional 10-ring zeolites.

SSZ-42: the first high-silica large pore zeolite with an undulating, one-dimensional channel system

The framework topology of the novel zeolite SSZ-42 is determined from single crystal data (15 × 15 × 35 µm) and refined from powder diffraction data; the crystalline architecture is characterized by an undulating, one-dimensional 12-membered ring channel system.