Structure-controlled, recyclable 3D-printed HZSM-5/bentonite monoliths for ex-situ catalytic cracking of polyethylene into monocyclic aromatics

Additive manufacturing offers a flexible route for fabricating materials with controlled architecture. This study developed 3D-printed multi-level porous HZSM-5 monoliths with engineered macro-channel patterns and evaluated them as heterogeneous catalysts for ex-situ cracking of linear low-density polyethylene (LLDPE) at 500 °C for 5 h. A two-stage, single-reactor configuration was established to integrate thermal cracking and catalytic upgrading within a single system. The printed monoliths preserved the MFI framework and retained approximately 70% of the parent zeolite surface area, decreasing from 404.9 to 292.7 m 2 /g after incorporation of a bentonite binder. Printing generated continuous channels and interconnected porosity, improving access to active regions and enabling controlled transport. Channel geometry served as a design variable, with straight and sinusoidal patterns providing different levels of vapor-catalyst contact. Across these architectures, the catalysts reduced light gases while favoring gasoline-range products with lower polyaromatic hydrocarbons (PAHs). For instance, C1–C3 selectivity decreased from 33% for the powder catalyst to around 9% for the printed monoliths (≈70% reduction), while PAHs declined from 22.6 to about 4.9% (≈80% reduction). Coke formation remained modest at approximately 5 wt% of the catalyst. Oxidative regeneration showed a “positive regeneration” response, removing about 60% of the deposited carbon, reducing the residual mass from ∼50.3 to ∼46.8 wt% while restoring pore accessibility and preserving moderate acidity. This promoted recovery of selective catalytic performance after regeneration. Overall, the results demonstrate that 3D-printed HZSM-5 monoliths provide a robust, regenerable platform for the efficient upgrading of plastic-derived vapors.