Temperature-controlled diffusion filter in multiscale confined spaces: exploring micro–mesoporous interfaces

The introduction of mesopores into microporous materials is often assumed to improve the diffusion properties. However, our findings reveal that hierarchical zeolites (containing both microporous and mesoporous structures), demonstrate enhanced diffusion properties compared with purely microporous zeolites only at elevated temperatures. By contrast, at lower temperatures, the diffusion performance is notably compromised. Rapid diffusion in hierarchical zeolites is widely recognized to rely on the full utilization of mesopores. Here, we emphasize that the prerequisite for the full utilization of mesopores is that the molecules must be able to diffuse into the mesoporous region. This was closely related to the movement of molecules at the microporous–mesoporous interface, which acted as a temperature-controlled filter. At low temperatures, only a small fraction of the molecules successfully traversed the interface and diffused into the mesopores, while the majority underwent ineffective collisions and diffused along the interface edges. By contrast, at high temperatures, the increased molecular collisions at the interface enhance the probability of successful traversal, enabling molecules to diffuse directly across the mesopores, significantly increasing the effective diffusion length. Furthermore, an in-depth analysis of the correlation between the molecular velocity, angle, and success rate of the mesopore entry and exit was conducted. These findings deepen our understanding of molecular diffusion in multiscale porous structures and offer critical insights into the design and optimization of high-performance hierarchical zeolites.