Cnudde Pieter, Redekop Evgeniy A, Dai Weili, Porcaro Natale G, Waroquier Michel, Bordiga Silvia, Hunger Michael, Li Landong, Olsbye Unni, Van Speybroeck Veronique
Center for Molecular Modeling (CMM), Ghent University, Technologiepark 46, 9052, Zwijnaarde, Belgium.
Center for Materials Science and Nanotechnology (SMN), Department of Chemistry, University of Oslo, P.O. Box 1126 Blindern, 0318, Oslo, Norway.
Angew Chem Int Ed Engl. 2021 Apr 26;60(18):10016-10022. doi: 10.1002/anie.202017025. Epub 2021 Mar 12.
The diffusion of saturated and unsaturated hydrocarbons is of fundamental importance for many zeolite-catalyzed processes. Transport of small alkenes in the confined zeolite pores 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.
饱和烃和不饱和烃的扩散对于许多沸石催化过程至关重要。小分子烯烃在受限的沸石孔道中的传输可能会受阻，从而对最终产物的选择性和分离产生重大影响。在此，通过一组互补的第一性原理分子动力学模拟、脉冲场梯度核磁共振（PFG-NMR）实验以及产物测量的脉冲响应时间分析，对沸石SAPO-34八元环窗口内晶体内轻质烯烃/石蜡的扩散进行了表征，从而在不同的长度和时间尺度上获取信息。我们的结果清楚地表明，布朗斯台德酸位点的存在对乙烯和丙烯的扩散速率具有促进作用，而烷烃的传输对酸位点的存在不敏感。红外光谱测量证实，不饱和烃扩散率的提高归因于与酸质子形成了有利的π-H相互作用。酸位点分布被证明是优化产物分布和分离的重要设计参数。
