Regulating framework aluminum location towards boosted light olefins generation in ex-situ catalytic pyrolysis of low-density polyethylene

Amidst the global focus on recycling and treatment of waste plastics for resource sustainability, it remains an enormous challenge to convert waste plastics into light olefin. Herein, the impact of framework Al (AlF) location in ZSM-5 catalyst, controlled by regulating Al sources, on the ex-situ catalytic pyrolysis of low-density polyethylene (LDPE) has been investigated. Based on multi-techniques, such as 27Al MAS NMR, ICP-AES, Co-UV-visDRS, XRD, SEM, N2 adsorption-desorption, NH3-TPD, Py-IR and FTIR. It is found that the AlF located at the channel intersections show more Al pairs, and this location offers ample space for secondary reactions, which include Diels-Alder reaction, cyclization reaction and dehydrogenation reaction, resulting in the low yield of light olefins (10.6 wt%) and the generation of light alkanes and aromatics from light olefins. In contrast, AlF located in the straight and sinusoidal channels exists mainly in the form of single Al. The substantial steric hindrance for this location facilitates the cracking reaction, mainly referring to the cracking reactions of LDPE that produce light olefins and generate enhanced yield of light olefins (52.8 wt%). These results provide new perspectives towarding boosted light olefins generation in ex-situ catalytic pyrolysis of LDPE.