A diffusion anisotropy descriptor links morphology effects of H-ZSM-5 zeolites to their catalytic cracking performance

The morphology of zeolites influences their catalytic activity, but defining descriptors to link morphology and activity is challenging. Here, time-resolved in situ FT-IR spectroscopy and MD simulations reveal that the difference in the catalytic performance of a series of H-ZSM-5 zeolites with similar sheet-like morphology can be attributed to intracrystalline diffusive propensities in different channels. Zeolite morphology is crucial in determining their catalytic activity, selectivity and stability, but quantitative descriptors of such a morphology effect are challenging to define. Here we introduce a descriptor that accounts for the morphology effect in the catalytic performances of H-ZSM-5 zeolite for C-4 olefin catalytic cracking. A series of H-ZSM-5 zeolites with similar sheet-like morphology but different c-axis lengths were synthesized. We found that the catalytic activity and stability is improved in samples with longer c-axis. Combining time-resolved in-situ FT-IR spectroscopy with molecular dynamics simulations, we show that the difference in catalytic performance can be attributed to the anisotropy of the intracrystalline diffusive propensity of the olefins in different channels. Our descriptor offers mechanistic insight for the design of highly effective zeolite catalysts for olefin cracking.

Automated summary

The morphology of zeolites plays a crucial role in determining their catalytic activity, selectivity, and stability, but it is challenging to define quantitative descriptors for this morphology effect. By introducing a new descriptor, the study successfully explains the morphology effect of sheet-like zeolites in C-4 olefin catalytic cracking, leading to improved catalytic activity and stability in samples with longer c-axis lengths. Time-resolved in-situ FT-IR spectroscopy and molecular dynamics simulations provide mechanistic insights for designing highly effective zeolite catalysts for olefin cracking.