Aluminosilicate Zeolite EMM-28 Containing Supercavities Determined by Continuous Rotation Electron Diffraction

Abstract

A new aluminosilicate zeolite, denoted EMM-28, has been successfully synthesized on a large scale using 1,1-(3,3-(1,3-phenylene)bis(propane-3,1-diyl))bis(1-methylpyrrolidinium) hydroxide as an organic structure directing agent (OSDA), which was scaled up to an ∼20 g scale with a yield of 77%. It crystallizes as thin plates (40-100 nm in thickness), and the corresponding powder X-ray diffraction (PXRD) pattern shows significant peak broadening which makes it insufficient for structure determination. Continuous rotation electron diffraction (cRED) data collected from 13 crystals were successfully used to solve and refine the structure of EMM-28. This illustrates that cRED data are capable of performing structure determination despite limited PXRD data quality. EMM-28 has a unique framework structure containing supercavities, >21 Å in size, connected by one-dimensional 10-ring channels. High-resolution transmission electron microscopy (HRTEM) confirmed the structure model. The structure of EMM-28 is related to several known zeolite structures with large cavities.

Figure 1

(A) 1,1-(3,3-(1,3-Phenylene)bis(propane-3,1-diyl))bis(1-methylpyrrolidinium) cation was used as the organic structure directing agent (OSDA) in the synthesis of EMM-28. (B) SEM micrograph of the EMM-28 crystal with a thickness of about 40–100 nm.

Figure 2

²⁹Si MAS NMR spectra of EMM-28. As-made material is shown in green as well as after different stages of treatment: calcined (orange), steamed at 700 °C (blue), and further steamed at 900 °C (dark blue). The sample survived the steaming at 900 °C (superimposed spectra at top). Deconvolution of the data from the 700 °C steamed sample shows at least ten unique T-sites (right).

Figure 3

(A) Experimental PXRD data of calcined EMM-28. (B–D) Two-dimensional slices cut from the reconstructed three-dimensional lattice showing the (B) 0kl, (C) h0l, and (D) hk0 planes. Diffuse scattering is observed, shown as streaks along the b*-axis in (D).

Figure 4

(A) EMM-28 with its building units highlighted: non (red) and cas (yellow) and a double layer constituted by chains of TO₄ tetrahedra running along the a-axis (green). (B) A supercavity [4⁴5¹²6²⁰10²] with two side pockets connected to a 10-ring channel. (C) A fragment of the refined structure of EMM-28 viewed along the a-axis showing anisotropic atomic displacement parameters for T-atoms (T = Si/Al) and O-atoms.

Figure 5

Supercavity connected by one 10-ring channel in (A) EMM-28, (B) EU-1, and (D) MCM-22, two 10-ring channels in (E) NU-87, and 8-ring channels in (C) SSZ-45. All van der Waals oxygen atom diameters of 2.7 Å have been subtracted.

Figure 6

(A) Structure projection image along the a-axis, reconstructed using QFocus software from a through-focus series of 20 HRTEM images, showing the 10-ring channels in the structure of EMM-28. An inset shows Fourier transform (FT) from the image in (A). (B) Lattice averaged and symmetry-imposed projected potential map obtained by crystallographic image processing of the image in (A). The plane group symmetry pmm has been imposed.