Significance of ZSM-5 hierarchical structure on catalytic cracking: Intra- vs inter-crystalline mesoporosity

Zeolites with hierarchical pore structure have been significantly beneficial as heterogeneous catalysts since they provide better diffusion for reactant and product molecules. Herein, this work provides further insight into mesoporosity types of intracrystalline and inter-crystalline in hierarchical ZSM-5 zeolites through the catalytic cracking of low-density polyethylene (LDPE). Hierarchical H-ZSM-5 zeolites were synthesized using two different routes, i.e., templating method (H-ZSM-H1) and mesoporogen-free synthesis at low temperature (H-ZSM-H2), together with conventional microporous ZSM-5 (H-ZSM-M) as a benchmark, were studied for catalytic applications. The zeolite catalysts were characterized in detail using a series of characterizations, including of XRD, FTIR, SEM-EDX, TEM, N₂-sorption, and NH₃-TPD. It was found that the templating route resulted in the formation of intracrystalline mesopores, while the inter-crystalline mesopores were generated via the mesoporogen-free route at low temperature. Albeit having a lower amount of acid sites, the sample with inter-crystalline mesopores exhibited better performance in LDPE cracking as proven by the significant improvement in lowering the observed activation energy.