High‐Silica Zeolite SSZ‐61 with Dumbbell‐Shaped Extra‐Large‐Pore Channels

The synthesis of the high‐silica zeolite SSZ‐61 using a particularly bulky polycyclic structure‐directing agent and the subsequent elucidation of its unusual framework structure with extra‐large dumbbell‐shaped pore openings are described. By using information derived from a variety of X‐ray powder diffraction and electron microscopy techniques, the complex framework structure, with 20 Si atoms in the asymmetric unit, could be determined and the full structure refined. The Si atoms at the waist of the dumbbell are only three‐connected and are bonded to terminal O atoms pointing into the channel. Unlike the six previously reported extra‐large‐pore zeolites, SSZ‐61 contains no heteroatoms in the framework and can be calcined easily. This, coupled with the possibility of inserting a catalytically active center in the channel between the terminal O atoms in place of H⁺, afford SSZ‐61 intriguing potential for catalytic applications.     

PKU-5: an aluminoborate with novel octahedral framework topology

A new anhydrous aluminoborate Al4B6O15 (PKU-5) has been synthesized in a boric acid flux in a closed system at 350 degrees C. PKU-5, which crystallizes in the space group R3 with the lattice constants a=11.43398(9) and c=6.48307(5) A, consists of Al octahedra and triangularly coordinated boron. The Al octahedron adopts the (10,3)-a network, in which each octahedron shares three edges with the neighboring octahedra forming ten-membered-ring channels. The octahedral backbone in PKU-5 can be considered as a primary octahedral framework topology and, setting out from the structures of the aluminoborates (PKU-1 and PKU-5), we propose construction rules for the octahedral frameworks. There are two types of connections for edge-sharing octahedra in porous frameworks, trans and cis type, by which various microporous octahedral frameworks of different topologies can be constructed. The borate groups share oxygens with the Al octahedral frameworks forming two kinds of three-membered-ring units consisting of two octahedra and one triangle (2Al+B) and one octahedron and two triangles (Al+2B), respectively.     

EU‐12: A Small‐Pore,High‐Silica Zeolite Containing Sinusoidal Eight‐Ring Channels

Zeolite EU‐12, the framework structure of which has remained unsolved during the past 30 years, is synthesized at a specific SiO₂/Al₂O₃ ratio using choline as an organic structure‐directing agent, with both Na⁺ and Rb⁺ ions present. Synchrotron powder X‐ray diffraction and Rietveld analyses reveal that the EU‐12 structure has a two‐dimensional 8‐ring channel system. Among the two distinct 8‐ring (4.6×2.8 and 5.0×2.7 Å) channels along c axis, the smaller one interconnects with the sinusoidal 8‐ring (4.8×3.3 Å) channel along a axis. The other large one is simply linked up with the sinusoidal channel by sharing 8‐rings (4.8×2.6 Å) in the ac plane. The proton form of EU‐12 was found to show a considerably higher ethene selectivity in the low‐temperature dehydration of ethanol than H‐mordenite, the best catalyst for this reaction.     

An Aluminophosphate Molecular Sieve with 36 Crystallographically Distinct Tetrahedral Sites

The structure of the new medium‐pore aluminophosphate molecular sieve PST‐6 is determined by the combined use of rotation electron diffraction tomography, synchrotron X‐ray powder diffraction, and computer modeling. PST‐6 was prepared by calcination of another new aluminophosphate material with an unknown structure synthesized using diethylamine as a structure‐directing agent, which is thought to contain bridging hydroxy groups. PST‐6 has 36 crystallographically distinct tetrahedral sites in the asymmetric unit and is thus crystallographically the most complex zeolitic structure ever solved.     

The role of crystallization parameters for the synthesis of germanosilicate with UTL topology

The investigation of the critical synthesis parameters of germanosilicate of UTL topology, possessing 14- and 12-rings, has been carried out in detail. (6R,10S)-6,10-Dimethyl-5-azoniaspiro[4.5]decane hydroxide was used as the structure-directing agent (SDA). The kinetics of the synthesis, the role of the Si/Ge ratio in the synthesis mixture, and the effect of the calcination procedure were investigated in relation to the crystallinity and textural properties of the synthesized material. The optimum synthesis time was found to be six days for Si/Ge and (Si+Ge)/SDA molar ratios of 2 and 1.7, respectively. The UTL zeolite crystallizes as small sheets of 10 mum in size. The micropore volume of the best crystals is 0.22 cm(3) g(-1) with a micropore diameter of 1.05 nm, based on DFT and Saito-Foley analyses of adsorption data.     

A Germanosilicate Structure with 11×11×12‐Ring Channels Solved by Electron Crystallography

Zeolites have been widely used in industry owing to their ordered micropores and stable frameworks. The pore sizes and shapes are the key parameters that affect the selectivity and efficiency in their applications in catalysis, sorption, and separation. Zeolites with pores defined by 10 and 12 TO₄ tetrahedra are often used for various catalytic processes. To optimize the performance of zeolites, it is extremely desirable to fine‐tune the pore sizes/shapes. The first germanosilicate zeolite with a three‐dimensional 11×11×12‐ring channel system, PKU‐16 (PKU, Peking University) is presented. Nanosized PKU‐16 was structurally characterized by the new three‐dimensional rotation electron diffraction (RED) technique. PKU‐16 is structurally related to the zeolite β polymorph C (BEC, 12×12×12‐ring channels) by rotating half of the four‐rings in double mtw units.     

Reverse‐Selective Microporous Membrane for Gas Separation

Sort the bigs from the smalls : Reverse‐selective membranes, through which bigger molecules selectively permeate, are attractive for developing chemical processes. A new adsorption‐based reverse‐selective membrane that utilizes a Na cation occluded in a zeolitic framework is presented. The membrane developed enables the selective permeation and separation of bigger polar molecules, such as methanol and water, from hydrogen above 473 K.

     

Cover Picture: Reverse‐Selective Microporous Membrane for Gas Separation (Chem. Asian J. 7/2009)

Reverse‐selective membranes , through which bigger molecules selectively permeate, are attractive for developing chemical processes utilizing hydrogen because they can maintain the high partial pressure of hydrogen required for further downstream utilization. Although several of these chemical processes are operated above 473 K, membranes with outstanding reverse‐selective separation performance at these temperatures are still to be reported. M. Matsukata et al. propose a new adsorption‐based reverse‐selective membrane that utilizes a Na cation occluded in a zeolitic framework. The membrane developed in this work enables selective permeation and separation of bigger polar molecules, such as methanol and water, from hydrogen above 473 K. For more information, see their Full Paper on page 1070 ff.

     

Two Aluminophosphate Molecular Sieves Built from Pairs of Enantiomeric Structural Building Units

Herein we report the synthesis and structures of two new small‐pore aluminophosphate molecular sieves PST‐13 and PST‐14 with mutually connected 8‐ring channels. The structure of PST‐13, synthesized using diethylamine as an organic structure‐directing agent, contains penta‐coordinated framework Al atoms bridged by hydroxy groups and thus edge‐sharing 3‐ and 5‐rings. Upon calcination, PST‐13 undergoes a transformation to PST‐14 with loss of bridging hydroxy groups and occluded organic species. The structures of both materials consist “nonjointly” of pairs of previously undiscovered 1,5‐ and 1,6‐open double 4‐rings (d4rs) which are mirror images of each other. We also present a series of novel chemically feasible hypothetical structures built from 1‐open d4r (sti) or 1,3‐open d4r (nsc) units, as well as from these two enantiomeric structural building units.