(660a) Multi-Scale Detection and Implication of 1D MEL Defects in 2D MFI Zeolite Nanosheets
AIChE Annual Meeting
2020
2020 Virtual AIChE Annual Meeting
Materials Engineering and Sciences Division
Synthesis and Application of Inorganic Materials II: Application/Separations
Friday, November 20, 2020 - 8:00am to 8:15am
Herein, using aberration-corrected transmission electron microscopy, we find that one- to few-unit-cells wide intergrowths of the zeolite MEL exist within 2D-MFI. The symmetry of MFI framework along the a-direction is broken by insertions of near-single-unit-cell domains of MEL. Because the MEL insertions are extended only along the c-direction, we call them 1-D or near 1-D-MEL. Fast Fourier transforms (FFT) of images with such MEL insertions show elongated spots along the a*-direction as compared to a typical MFI spot pattern. We identify the planar distribution of these 1-dimensional (1D) or near-1D-MEL domains using custom-built computational pattern matching techniques. Furthermore, we show that a fraction of individual nanosheets have high (ca. 25% by volume) MEL content while the majority of nanosheets are MEL-free through quantitative electron- and x-ray diffraction analysis.
Atomistic simulations suggest that atomic scale knitting of 1D-MEL within 2D-MFI creates more rigid and highly selective pores as compared to those in pristine MFI nanosheets. These enhanced properties of nanosheets are translated to MFI-MEL membranes which show an unprecedented separation factor of 60 using an industrially relevant (undiluted 1 bar xylene mixture) feed [3].
References
[1] M. Choi et al, Nature 461, (2009), 246-249.
[2] K. Varoon et al, Science 334, (2011), 72-75.
[3] P. Kumar et al, Nature Materials 19, (2020), 443-449.