Experimental and Theoretical Evidence for the Promotional Effect of Acid Sites on the Diffusion of Alkenes through Small‐Pore Zeolites
Open Access
- 26 January 2021
- journal article
- research article
- Published by Wiley in Angewandte Chemie
- Vol. 60 (18), 10016-10022
- https://doi.org/10.1002/anie.202017025
Abstract
The diffusion of saturated and unsaturated hydrocarbons is of fundamental importance for many zeolite‐catalyzed processes. Transport of small alkenes in the confined pores of narrow pore zeolites can become hindered, resulting in a significant impact on the ultimate product selectivity and separation. Herein, intracrystalline light olefin/paraffin diffusion through the 8‐ring windows of zeolite SAPO‐34 is characterized by a complementary set of first‐principle molecular dynamics simulations, PFG‐NMR experiments and pulse‐response Temporal Analysis of Products measurements, yielding information at different length and time scales. Our results clearly show a promotional effect of the presence of Brønsted acid sites on the diffusion rate of ethene and propene, whereas transport of alkanes is found to be insensitive to the presence of acid sites. The enhanced diffusivity of unsaturated hydrocarbons is ascribed to the formation of favorable π‐H interactions with acid protons, as confirmed by IR spectroscopy measurements. The acid site distribution is proven to be an important design parameter for optimizing product distributions and separations.Keywords
Funding Information
- European Research Council (240483)
- National Natural Science Foundation of China (21972069)
- Norges Forskningsråd (288331/O70 (CO2LO))
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