title: Ordered silicon vacancies in the framework structure of the zeolite catalyst SSZ-74.
abstract: 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.
authors.affiliation: Laboratory of Crystallography, ETH Zurich, CH-8093 Zurich, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Baerlocher
authors.forename: Dan
authors.initials: D
authors.lastname: Xie
authors.forename: Lynne B
authors.initials: LB
authors.lastname: McCusker
authors.forename: Son-Jong
authors.initials: SJ
authors.lastname: Hwang
authors.forename: Ignatius Y
authors.initials: IY
authors.lastname: Chan
authors.forename: Kenneth
authors.initials: K
authors.lastname: Ong
authors.forename: Allen W
authors.initials: AW
authors.lastname: Burton
authors.forename: Stacey I
authors.initials: SI
authors.lastname: Zones