Nanoporous materials, like zeolites and metal-organic frameworks, find widespread applications in catalysis and separation technologies. Their proper design requires a detailed understanding of the mass transfer mechanisms with their surroundings. This is conventionally deduced from so-called uptake or release curves carried out with batches of nanoporous crystals. The analysis of these batch uptake curves is based on the assumption that all crystals are identical. However, in this presentation, we will show that this approximation may lead to inaccurate conclusions about the material properties. As a consequence of the crystal diversity, the real governing uptake mechanism may be obscured by mimicked mass transfer mechanism. Various experimental and theoretical cases will be presented. Results obtained from single-crystal and multiple-crystals uptake measurements, using different experimental approaches, including a liquid phase batch methodology1 and the micro-imaging techniques2, will be shown. These experiments were performed with the catalyst of excellence for the Methanol-To-Olefins (MTO) process, namely the zeolite SAPO-343. Based on the experimental results, through a simple theoretical approach, several cases of batch uptake curves which are deformed by the crystal diversity will be shown and discussed in relation to the conventional analysis techniques.
J. Cousin Saint Remi is grateful to the Agency for Innovation by Science and Technology in Flanders (IWT) and The Research Foundation – Flanders (FWO) for the financial support.
Cousin Saint Remi, J., Baron, G. & Denayer, J. Nonuniform Chain-Length-Dependent Diffusion of Short 1-Alcohols in SAPO-34 in Liquid Phase. J. Phys. Chem. C, 2013, 117, 9758–9765.
Kärger, J. et al. Microimaging of transient guest profiles to monitor mass transfer in nanoporous materials. Nat. Mater. 2014, 13, 333–343.
Stocker, M. Methanol-to-Hydrocarbons: Catalytic Materials and Their Behavior. Micropor. Mesopor. Mat. 1999, 29, 3-48.
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