EMM-25 The Structure of Two-Dimensional 11 x 10 Medium-Pore Borosilicate Zeolite Unraveled Using 3D Electron Diffraction

• Published in: Chemistry of materials Vol. 33; no. 11; p. 4146
• Main Authors: Cho, Jung, Yun, Yifeng, Xu, Hongyi, Sun, Junliang, Strohmaier, Karl G., Terefenko, Gene, Vroman, Hilda, Afeworki, Mobae, Cao, Guang, Wang, Hao, Zou, Xiaodong, Burton, Allen V., Willhammar, Tom
• Format: Journal Article
• Language: English
• Published: 08.06.2021
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.1c00892

The structure of the novel medium-pore borosilicate zeolite EMM-25 has been determined by continuous rotation electron diffraction (cRED). EMM-25 crystallizes in the space group Cmcm with unit cell parameters a = 11.055, b = 22.912, and c = 24.914 angstrom and a composition of IC4H8(C11H25N)(2)I (2)[Si112.5B3.5O232]. The EMM-25 framework possesses a two-dimensional channel system composed of 10-ring channels connected via 11-ring windows. Its channel system is analogous to that of the medium-pore zeolite NU-87 framework but with 11- rather than 12-ring windows, suggesting a different shape selectivity. EMM-25 was first obtained using 1,4-bis(N-methyl-N,N-dihexylammonium)butane as an organic structure directing agent (OSDA). Based on a molecular docking study of the OSDA within the pores of the determined framework structure, a new ammonium dication OSDA with an improved fit was devised. By using this new OSDA, the synthesis time was reduced 80%, from 52 to just 10 days. Furthermore, cRED data revealed a structural disorder of the EMM-25 framework present as swinging zigzag chains. The introduction of the disorder, which is a consequence of geometry relaxation, was crucial for an accurate structure refinement. Lastly, the cRED data from as-made EMM-25 showed residual potential consistent with the location of the OSDA position determined from the Rietveld refinement, concluding a complete refinement of the as-made structure based on the cRED data.