In-depth understanding of the synergistic effect in catalytic copyrolysis of lignin-plastic mixtures with lignin-tailored hierarchical HZSM‑5 catalysts

To overcome the diffusion limitations of DZSM-5 and increase the yield of hydrocarbon-rich bio-oil, a structurally tailored hierarchical catalyst was synthesized via alkaline treatment and waste biomass-derived lignin-assisted reassembly. The physicochemical properties, such as the crystallinity, porosity, acidity and morphology, were characterized with various methods. The catalytic activities were evaluated with various lignin doping contents and lignin-to-LDPE ratios. Additionally, the product distributions, reaction mechanisms and reusability were also investigated. A detailed experiment suggested that lignin significantly increased the porosity of the hierarchical catalyst and led to the formation of a well-developed micro-mesoporous structure via lignin doping reassembly, which facilitated the passage of pyrolysis volatiles. Additionally, the increased porosity and intracrystalline mesoporosity of the material resulted in excellent dehydrogenation, decarbonylation and β-O-4 cleavage activities. Lower lignin doping levels produced olefins and alkylbenzenes and inhibited PAH formation; in contrast, higher lignin loadings facilitated aromatics and BTXE formation. A synergistic effect between the lignin and LDPE was observed for HCs formation with enhanced hydrogen transfer and Diels-Alder reactions. The optimal 0.50 % C@DZSM-5 exhibited excellent catalytic activity, with a hydrocarbon yield of 71.29 % and an olefin selectivity of 30.78 % at a lignin-to-LDPE ratio of 1:1. Furthermore, 0.50 % C@DZSM-5 exhibited good reusability and stability after three runs, and ∼95 % of the content was maintained. The micropore specific surface area coverage and micropore volume blockage were the main reasons for catalyst deactivation.