Hierarchical Accessibility and Framework-Al Organization in Ultra-High-Silica ZSM-5 Enable Efficient Cracking of...

Selective conversion of waste polyolefins to light olefins offers a promising route for waste-plastic valorization but is often limited by the trade-off between cracking activity and secondary reactions over acidic zeolites. Here we report a tetrapropylammonium hydroxide-directed synthesis strategy assisted by cetyltrimethylammonium bromide (CTAB) and tert-butanol (TBA) to construct an ultra-high-silica hierarchical ZSM-5 with a highly isolated framework-Al distribution within a low-acidity environment. Under hydrogen-free conditions at 450°C, the optimized catalyst CTAB_2.5/TBA₅-ZSM-5 achieves a gas yield of 95.3 wt%, a C_2-C₄ olefin selectivity of 88.2% in the gas phase, and a light-olefin yield of 84.0 wt%, while maintaining a light-olefin yield of ∼77 wt% over 20 consecutive cycles without regeneration. The catalyst also maintains high gas yields and light-olefin selectivity across representative post-consumer polyolefin feedstocks. Structural and catalytic analyses show that the superior performance stems from enhanced mass transport through the hierarchical pore network coupled with a highly isolated, channel-preferential framework-Al distribution, thereby suppressing deep secondary conversion. The concerted control of hierarchical accessibility and framework-Al distribution in low-acidity zeolites offers a useful framework for designing efficient polyolefin-cracking catalysts.