Tandem catalytic cracking of LDPE to C2-C4 olefins over interconnected NZ@Al-meso-SiO2: Role of hierarchical porosity and acidity

Catalytic upcycling offers a promising route to valorize end-of-life polyolefins as high-value chemicals, yet significant challenges remain. Adjusting the hierarchical porosity and acidity of composites can effectively enhance polyolefins cracking efficiency. Thus, systematically studying their effects on cracking performance is essential. In the presented work, the interconnected NZ@Al-meso-SiO₂ composites are synthesized for the efficient tandem catalytic cracking of low-density polyethylene (LDPE) into light olefins (C₂-C₄). By adjusting the ZSM-5/meso-SiO₂ mass ratio and the Si/Al atomic ratio, the impact of hierarchical porosity and acidity on product distribution was systematically investigated. The results indicated that medium ZSM-5/meso-SiO₂ mass ratio (n = 0.3) facilitates the tandem cracking of LDPE and enhances mass transfer. The Al-meso-SiO₂ component selectively pre-cracks LDPE into intermediates and subsequently timely diffusion and deep cracking of the intermediates in nanosized ZSM-5, ultimately converting into C₂-C₄ olefins. The low Si/Al ratio (50) demonstrates a high acid density and the Brønsted/Lewis (B/L) acid ratio, exhibits greater selectivity for light olefins compared to a higher Si/Al ratio. The optimized NZ@Al-meso-SiO₂-0.3–50 delivers an impressive performance, achieving ∼50 wt% light olefin yields at 550 °C within just 15 min. This exceptional activity and selectivity significantly surpass conventional single-component catalysts, physical mixtures, as well as exceeding results reported in the literature. This rational design of synergistic tandem catalysts provides a powerful foundation for developing advanced composite materials for diverse catalytic upcycling and reaction processes.