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

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 infinity. However, an increase in Br & oslash;nsted 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 Br & oslash;nsted 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.