Insight into the effect of Si/Al ratio on the adsorption and diffusion behavior of butane isomers in HZSM-5 zeolites

Abstract

The adsorption and diffusion properties of zeolite materials for molecules depend on their pore structure and acidic properties, which have a profound impact on their catalytic performance. In this work, the influence mechanism of the Si/Al ratio on the adsorption and diffusion behaviors of n-butane and isobutane in HZSM-5 zeolites was investigated via Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods. It is found that the difference in adsorption amount of n-butane and isobutane is not significant in MFI zeolites with varying the Si/Al ratio from 12 to ∞. However, an increase in Brønsted acidity of HZSM-5 can significantly influence the adsorption modes of butane, as analyzed through a parameter of the probability distribution of nearest distance (PDND) techniques. The diffusion of n-butane was impeded by the Brønsted acid site, particularly at low loading, due to increased collisions with H atoms at the active site. Furthermore, the relationship between the diffusion and the adsorption probability of n-butane in the straight channel was built. These findings contribute to a deeper understanding of adsorption and diffusion behaviors and their influencing factors, including pore structure and modifications, which are of great significance to the rational design of zeolite catalytic materials.

Graphical abstract