Effect of particle size of single-crystalline hierarchical ZSM-5 on its surface mass transfer in n-heptane catalytic cracking

Single-crystalline hierarchical ZSM-5 zeolites with different particle sizes (namely 100, 140, and 200 nm) were successfully prepared by adjusting the amount of tetrapropylammonium hydroxide (TPAOH), and investigated in n-heptane catalytic cracking reaction. Diffusional measurements by zero-length column (ZLC) method showed that the apparent diffusivities of n-heptane decreased with the reduction of particle size, indicating the existence of surface barriers. Moreover, with the decrease of particle size, the additional diffusion path length increased, which meant the influence of surface barriers became more apparent. Despite the change of surface barriers, the intracrystalline diffusion still dominated the overall diffusion. Catalytic performance showed that the zeolite with smaller particle size had better stability.