Diffusion anisotropy descriptor revealing morphology effect of H-ZSM-5 zeolite for olefin catalytic cracking
Abstract Zeolite morphology is vital in determining catalytic activity, selectivity and stability in zeolite catalysis, while quantitative description of morphology effect is great challenging but highly desirable. Herein, a descriptor to elucidate the morphology effect is proposed by revealing the diffusion anisotropy in straight and sinusoidal channels of H-ZSM-5 zeolite for olefin catalytic cracking. A series of H-ZSM-5 zeolites with similar nano-sheet morphology were precisely synthesized in which only the length in c-axis varies. It is unexpectedly demonstrated that the catalytic activity and stability can be obviously improved by employing samples with longer length in c-axis. Combining time-resolved in-situ FT-IR spectroscopy with molecular dynamic simulations, we revealed that the difference in catalytic performance can be attributed to the intracrystalline diffusive propensity in different channels. This work not only provides a clear descriptor revealing morphology effect, but also offers deep insight into design of highly effective zeolite catalysts for olefin catalytic cracking.