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EMM-23: A Stable High-Silica Multidimensional Zeolite with Extra-Large Trilobe-Shaped Channels

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posted on 01.10.2014, 00:00 by Tom Willhammar, Allen W. Burton, Yifeng Yun, Junliang Sun, Mobae Afeworki, Karl G. Strohmaier, Hilda Vroman, Xiaodong Zou
Stable, multidimensional, and extra-large pore zeolites are desirable by industry for catalysis and separation of bulky molecules. Here we report EMM-23, the first stable, three-dimensional extra-large pore aluminosilicate zeolite. The structure of EMM-23 was determined from submicron-sized crystals by combining electron crystallography, solid-state nuclear magnetic resonance (NMR), and powder X-ray diffraction. The framework contains highly unusual trilobe-shaped pores that are bound by 21–24 tetrahedral atoms. These extra-large pores are intersected perpendicularly by a two-dimensional 10-ring channel system. Unlike most ideal zeolite frameworks that have tetrahedral sites with four next-nearest tetrahedral neighbors (Q4 species), this unusual zeolite possesses a high density of Q2 and Q3 silicon species. It is the first zeolite prepared directly with Q2 species that are intrinsic to the framework. EMM-23 is stable after calcination at 540 °C. The formation of this highly interrupted structure is facilitated by the high density of extra framework positive charge introduced by the dicationic structure directing agent.