Enhancement of aromatics selectivity in waste LLDPE with HZSM-5@MCM-41 Core-Shell catalysts synthesized by One-Step hydrothermal method

In order to alleviate the pressure on environmental governance caused by waste plastics and to promote the development of a circular economy, this study proposed a HZSM-5@MCM-41 catalyst prepared by a simple one-step hydrothermal method to convert plastics into aromatic hydrocarbons, especially monocyclic aromatic hydrocarbons. HZSM-5, known for its outstanding shape-selective catalytic properties, is widely used in plastic pyrolysis. However, its microporous structure inherently restricts the diffusion of large-molecule compounds. The study revealed that by introducing the mesoporous MCM-41 layer, the specific surface area and pore volume increased by more than 50% compared to HZSM-5. Additionally, by adjusting the Si/Al ratio, the catalyst exhibited a high density of weak acid sites and a low density of strong acid sites. These improvements effectively optimized the pore structure and acid site distribution of the catalyst, ultimately enhancing the catalytic activity HZSM-5@MCM-41. Consequently, the optimized catalyst achieved the highest AHs and MAHs selectivity to 89.45% and 72.03%, respectively, for the pyrolysis of LLDPE. Furthermore, the performance tests of regenerated catalyst showed that the selectivity to MAHs remained at 90% of the initial value after five regenerations of HZSM-5@MCM-41. Finally, based on the “structure–activity relationship” between the microstructure of the core–shell catalyst and its catalytic performance, a diffusion–reaction mechanism for plastic degradation was presented, providing valuable insights into the sustainable transformation of waste plastics into high-value chemical products.