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

Abstract

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 Å and a composition of |C4H8(C11H25N)2|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.

Tunable CHA/AEI Zeolite Intergrowths with A Priori Biselective Organic Structure‐Directing Agents: Controlling Enrichment and Implications for Selective Catalytic Reduction of NOx

“…One approach to obtain atomic resolution images with an improved signal‐to‐noise ratios, is by using iDPC STEM. This method has recently been used to study the surface structure of MOFs [23] and species inside zeolite pores [24–26] . A second emerging method is scanning electron diffraction (SED, also called 4DSTEM).…”

“…This method has recently been used to study the surface structure of MOFs [23] and species inside zeolite pores. [24][25][26] A second emerging method is scanning electron diffraction (SED, also called 4DSTEM). In this approach, a small (< 5 nm) electron probe with a small convergence angle is raster-scanned across a sample and a diffraction pattern is acquired from each beam position to build up a map.…”

Structure of the active pharmaceutical ingredient bismuth subsalicylate

“…Concurrently, aberration-corrected high-resolution scanning transmission electron microscopy (STEM) has evolved into an essential technique for atomic-scale structural investigations, particularly of local disorder. The recent development of STEM techniques such as integrated differential phase contrast (iDPC) has allowed for studies on beam-sensitive specimens, including studies of organic molecules inside inorganic framework materials 35 , 36 .…”