Eco-synthesis of single-crystalline hierarchical ZSM-5 zeolites for advanced catalysis: A dextran-mediated approach

Single-crystalline hierarchical zeolites are highly promising for petrochemical and green chemistry applications, but their synthesis traditionally relies on halogen- and/or nitrogen-containing organic templates whose removal through calcination poses serious environmental pollution. Herein, we present a green, halogen- and nitrogen-free approach for single-crystalline hierarchical ZSM-5 zeolite synthesis using dextran as a bifunctional template. Theoretical calculations and experimental results reveal that dextran can induce the transformation of partial four-membered rings into five-membered rings during crystallization, and interact strongly with Si-OH and/or Al-OH groups through hydrogen bonding. Acting as a structure-directing agent, dextran not only stabilizes the five-membered rings formed in the precursor, but also facilitates the construction of the mobil five (MFI) zeolite framework through the interactions between the hydroxyl/α-CH groups and Si/Al species. Additionally, dextran aids in the directional arrangement of nanocrystals, and serves as a space-filling agent within the mesopores during synthesis. The resulting single-crystalline hierarchical ZSM-5 zeolite exhibits superior catalytic performance in low density polyethylene pyrolysis and methanol-to-propylene reactions. This work provides a sustainable and scalable strategy for synthesizing advanced zeolite nanomaterials, with broad implications for catalysis and green chemistry.