Structural Study of Micro- and Meso-porous Crystals by Electron Microscopy

Osamu Terasaki1, Juanfang Ruan1, Keiichi Miyasaka1, Yasuhiro Sakamoto1, Lu Han1,2, Sam M. Stevens1,3, Pablo Cubillas3, Kjell Jansson1, Shunsuke Asahina4, Michael W. Anderson3 and Shunai Che2

1Department of Physical, Inorganic & Structural Chemistry, Arrhenius Laboratory, Stockholm University, SE-10691 Stockholm, Sweden,

2School of Chemistry and Chemical Technology, State Key Laboratory of Composite Materials, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, P.R. China

3School of Chemistry, The University of Manchester, Oxford Road, Manchester M139LP, UK 4JEOL(Europe) SAS, Espace Claude Monet-1 all’ee de Giverrny, 78290 Croissy-Sur-Seine, France

Two classes of porous crystals, micro- and meso-, posses pores with diameters of dpore <20 Å and 20Å < dpore < 500Å, respectively [1]. Due to their small size, powder X-ray diffraction (XRD), rather than single crystal XRD, is usually performed. Unfortunately, the overlap of reflections owing to a large unit cell, the existence of structural defects/modulations for microporous crystals and small number of reflections for mesoporous crystals, create problems when solving their structures. However, single crystal structural information can still be collected by using electron microscopy (EM) together with phase information of the crystal structure factors through high-resolution TEM images. Synthesis of microporous crystals (zeolites) with new framework-type structures continues to be reported. Among the various synthetic approaches, interlayer expanded zeolites (IEZ) from layered silicate precursors are demonstrating great potential for synthesising new zeolites with larger pores and require systematic study [2]. Progress in high-resolution scanning EM (HRSEM) with low accelerating voltage illuminates the situation of crystal growth of the porous crystals. By combining HRSEM and atomic force microscopy (AFM), surface details can be studied to aid understanding of basic crystal growth processes for different type of zeolites [3]. Mesoporous crystals are structurally unique in that they exhibit an ordered arrangement of mesoscopic-scale channels, cages or pores yet with disorder on the atomic scale. For periodic systems, we have developed an electron crystallography method to obtain three dimensional structural solutions combined with knowledge of both pore volume and silica wall density [4]. By assessing the boundary energy, we have recently extended our method in order to obtain a self-consistent structural solution solely by a set of transmission EM (TEM) images [5]. We have also observed interesting TEM images showing defects in mesoporous crystals indicating structural relationships among the different structures [6]. At the conference the followings will be discussed: (i) New structures IEZ, (ii) HRSEM observations of zeolites and silica mesoporous crystals, (iii) Structure solutions of silica mesoporous crystals self-consistently solved solely from TEM images and (iv) Defects observed in silica mesoporous crystals. Acknowledgement We thank Dr T. Ohsuna for letting us to use his software and The Alice & Knut Wallenberg Foundation, Swedish Research Council (VR) and Japan Science and Technology Agency (JST) for financial supports. References [1] Mesoporous crystals and related nano-structured materials, ed. by O. Terasaki, Stud Surf Sci and Catal. 148, 2004. [2] J. Ruan et al., Angew. Chem. Int. Ed. 44, 2005, 6719 and to be submitted.

220

AMTC Letters Vol. 1 (2008)

© 2008 Japan Fine Ceramics Center

[3] S.M. Stevens et al., Chem. Commun., in print. [4] Y. Sakamoto et al., Nature 444, 2006, 79. [5] K. Miyasaka & O. Terasaki, to be submitted. [6] Y. Sakamoto et al., to be submitted and L. Han et al., to be submitted. Figure 1: HRTEM images and FDs of a) 3D Ti-MWW and b) Ti-YNU-1 taken with [100] direction. Red and black arrows represent the same MWW layer structure in 3D Ti-MWW and Ti-YNU-1. Figure 2: SEM (a), AFM error trace (b) and AFM height trace (c) of the (100) surface of zeolite A (a - inset, the area highlighted in white). Figure 3: HRTEM images of the defects observed in silica mesoporous crystal with Fd-3m. Schematic drawings of polyhedra and simulated images are inserted.

221

AMTC Letters Vol. 1 (2008)

© 2008 Japan Fine Ceramics Center