[231] One-dimensional-intergrowths in two-dimensional zeolite nanosheets and their effect on ultra-selective transport

P. Kumar, D.W. Kim, N. Rangnekar, H. Xu, E.O. Fetisov, S. Ghosh, H. Zhang, Q. Xiao, M. Shete, J.I. Siepmann, T. Dumitrica, B. McCool, M. Tsapatsis, and K.A. Mkhoyan

Nat. Mats. 19, 443–449 (2020)

Publication Abstract

Zeolite MFI is a widely used catalyst and adsorbent that also holds promise as a thin-film membrane. The discovery of nanometre-thick two-dimensional (2D) MFI nanosheets has facilitated methods for thin-film zeolite fabrication that open new horizons for membrane science and engineering. However, the crystal structure of 2D-MFI nanosheets and their relationship to separation performance remain elusive. Using transmission electron microscopy, we find that one- to few-unit-cell-wide intergrowths of zeolite MEL exist within 2D-MFI. We identify the planar distribution of these 1D or near-1D-MEL domains, and show that a fraction of nanosheets have high (~25% by volume) MEL content while the majority of nanosheets are MEL-free. Atomistic simulations show that commensurate knitting of 1D-MEL within 2D-MFI creates more rigid and highly selective pores compared to pristine MFI nanosheets, and permeation experiments show a separation factor of 60 using an industrially relevant (undiluted 1 bar xylene mixture) feed. Confined growth in graphite is shown to increase the MEL content in MFI nanosheets. Our observation of these intergrowths suggests strategies for the development of ultra-selective zeolite membranes.

Siepmann Group Authors
graphical abstract