Differentiating Diffusivity in Different Channels of ZSM-5 Zeolite by Pulsed Field Gradient (PFG) NMR

摘要

Differentiating the diffusivity in straight channel and sinusoidal channel of ZSM-5 zeolite is a prerequisite for catalyst optimization for the required product distribution with specific orientation. Herein, the intracrystalline diffusivities of n-butane and iso-butane in power ZSM-5 zeolite were investigated by pulse field gradient (PFG) NMR, respectively. Different diffusion behaviors of the selected isomers were revealed. The effective self-diffusion coefficient of n-butane is about three orders of magnitude higher than that of iso-butane. For the selected isomers, the opposite loading-dependence were presented in self-diffusion coefficients. Moreover, an equation containing diffusion tensors in different directions in orthogonal coordinate was successfully applied to fit the diffusion coefficients of n-butane in straight and sinusoidal channel of ZSM-5, respectively. The diffusivity of n-butane in straight channel is nearly one order of magnitude faster than that in sinusoidal channel, predicting its dominant diffusion path.