Abstract
Nanoporous materials find widespread applications in our society: from drug delivery to environmentally friendly catalysis and separation technologies1,2,3,4,5,6. The efficient design of these processes depends crucially on understanding the mass transfer mechanism. This is conventionally determined by uptake or release experiments, carried out with assemblages of nanoporous crystals, assuming all crystals to be identical. Using micro-imaging techniques7, we now show that even apparently identical crystals (that is, crystals of similar size and shape) from the same batch may exhibit very different uptake rates. The relative contribution of the surface resistance to the overall transport resistance varied with both the crystal and the guest molecule. As a consequence of this crystal diversity, the conventional approach may not distinguish correctly between the different mass transfer mechanisms. Detection of this diversity adds an important new piece of evidence in the search for the origin of the surface barrier phenomenon. Our investigations were carried out with the zeolite SAPO-34, a key material in the methanol-to-olefins (MTO) process8, propane–propene separation9,10 and adsorptive heat transformation11.
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Acknowledgements
J.C.S.R. is grateful to the Agency for Innovation by Science and Technology in Flanders (IWT) and the Research Foundation—Flanders (FWO—Vlaanderen) for their financial support. Graphical content was supported by Visuality (BE). Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie are acknowledged for establishing the micro-imaging system in Leipzig. Valuable discussions with D. M. Ruthven are particularly appreciated.
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J.C.S.R., C.C., J.F.M.D. and J.K. contributed to the development of the experimental approach. J.C.S.R. and A.L. conducted the interference microscopy experiments; C.C. and A.L. performed the infrared microscopy measurements; J.C.S.R., C.C. and J.K. contributed to the initial ideas and interpreting experimental data; J.C.S.R., G.V.B. and J.F.M.D. supported the material characterization. J.C.S.R. provided the batch uptake simulations. I.V. and H.T. ensured the performance of the FE-SEM, AFM, XPS and EDX measurements, which were realized by J.C.S.R. All authors participated in the writing of the manuscript.
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Remi, J., Lauerer, A., Chmelik, C. et al. The role of crystal diversity in understanding mass transfer in nanoporous materials. Nature Mater 15, 401–406 (2016). https://doi.org/10.1038/nmat4510
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DOI: https://doi.org/10.1038/nmat4510
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