Catalytic co-pyrolysis of waste lignin and polyethylene over Fe modified HZSM-5/SBA-15 core–shell catalyst for the enhancement of aromatics

The development of efficient metal-modified core–shell molecular sieve catalysts for the catalytic co-pyrolysis of lignin and plastics to produce aromatics is an effective way to achieve high-value utilization of waste materials. In this study, x-Fe@HZSM-5/SBA-15 (x-Fe@H/S) catalysts (x represents Si/Al) of HZSM-5 cores with Fe-Si-Al as the backbone were synthesized by isomorphous substitution and covered with an SBA-15 shell. The effects of the Si/Al ratio and Fe isomorphously substituted Al in the catalysts on the product distribution, and the formation characteristics of aromatics were investigated during the co-pyrolysis of dealkalized lignin (DL) and high-density polyethylene (HDPE). The catalyst’s cyclic regeneration performance was also analyzed. The results indicated that the pore size and acidic site distribution of the catalysts could be regulated by the Si/Al ratio, thereby promoting aromatics formation. Among them, 50-Fe@H/S exhibited the best performance, with high activity, appropriate mesopore size, and moderate acidity (0.25 mmol/g), achieving the highest bio-oil content (20.54 wt%) and aromatics content (25.96 area%). Meanwhile, the regenerated 50-Fe@H/S maintained satisfactory catalytic performance. Based on the experimental results, the aromatics formation pathways during catalytic co-pyrolysis over x-Fe@H/S were proposed, and the effects of Fe incorporation were analyzed using density functional theory.