Synthesis of ZSM-5 with hierarchical porosity: In-situ conversion of the mesoporous silica-alumina species to hierarchical zeolite

Hierarchical ZSM-5 aggregates were fabricated using the conventional surfactant cetyltrimethylammonium bromide (CTABr) as the mesoporogen together with 1, 6-diaminohexane (HDA) as structure-directing agent. The competition of the templates and the subsequent phase separation were effectively avoided. A possible formation mechanism was proposed based on the investigation of the crystallization process. The obtained hierarchical ZSM-5 aggregates were highly crystallized, possessing large external surface area, mesopore volume and regular mesopore size distributions. And they were proved to be more efficient in catalytic LDPE cracking due to improved accessibility of large polymer molecules to the active sites. This method was facile and cost-effective, applicable within a wide SiO₂/Al₂O₃ratio by using various silica sources.