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In a paper just published in Science Advances, researchers report synergetic enhancement between sorption and diffusion in zeolites with continuum intersecting channels. The research was performed by a Chinese research team led by Prof. Anmin Zheng at the Wuhan Institute of Physics and Mathematics of the Chinese Academy of Sciences. HIMS Prof. em. Rajamani Krishna, along with Dr Jasper van Baten (formerly at HIMS) assisted with molecular simulations, data analysis and interpretation.

Image from paper
Channels and diffusion coefficients in the SCM-15 zeolite. (A) 3D channels in the SCM-15 zeolite. 1D channels along the (B) X, (C) Y, and (D) Z directions. The silver balls represent intersections. The green, blue, and orange cylinders represent channels along the X, Y, and Z directions, respectively. The small blue and orange balls represent atoms in the Y and Z channels, respectively (discrete intersections). All atoms in the X channels are located in the intersections (continuum intersections), and so, no small green balls are shown. (E) Variations in the anisotropic diffusivity of p-xylene molecules inside the SCM-15 zeolite as a function of loading (pressure) along the X, Y, and Z directions and as a function of total loading (S) at 298 K. (F) Variations in anisotropic diffusion coefficient ratio of p-xylene molecules as a function of loading (298 K). Image: Science Advances.

Abstract

In separation and catalysis applications, adsorption and diffusion are normally considered mutually exclusive. That is, rapid diffusion is generally accompanied by weak adsorption and vice versa. In this work, we analyze the anomalous loading-dependent mechanism of p-xylene diffusion in a newly developed zeolite called SCM-15. The obtained results demonstrate that the unique system of “continuum intersecting channels” (i.e., channels made of fused cavities) plays a key role in the diffusion process for the molecule-selective pathways. At low pressure, the presence of strong adsorption sites and intersections that provide space for molecule rotation facilitates the diffusion of p-xylene along the Z direction. Upon increasing the molecular uptake, the adsorbates move faster along the X direction because of the effect of continuum intersections in reducing the diffusion barriers and thus maintaining the large diffusion coefficient of the diffusing compound. This novel mechanism synergistically improves the diffusion of hydrocarbons in zeolites.

Paper

Zhiqiang Liu, Jiamin Yuan, Jasper M. van Baten, Jian Zhou, Xiaomin Tang, Chao Zhao, Wei Chen, Xianfeng Yi, Rajamani Krishna, German Sastre, Anmin Zheng: Synergistically enhance confined diffusion by continuum intersecting channels in zeolites Sci. Adv. 2021; 7, eabf0775 (2021). DOI: 10.1126/sciadv.abf0775