Improvement of Aromatics Selectivity from Catalytic Pyrolysis of Low-Density Polyethylene with Metal-Modified HZSM-5 in a CO2 Atmosphere

Catalytic pyrolysis has been emerging as a promising strategy to tackle solid pollution induced by waste plastics, whereas achieving high selectivity of targeted products like valuable light aromatics remains a huge challenge. In this work, a novel protocol that combing waste plastic conversion and greenhouse gas CO2 utilization was proposed for the first time. Different metal (Fe, Ni, Co, Mn, Ag, and Cu)-modified HZSM-5 zeolites were fabricated and then used as catalysts for the catalytic pyrolysis of low-density polyethylene (LDPE) with CO2 as the reaction atmosphere. The introduction of CO2 enhanced the selectivity of aromatic hydrocarbons from LDPE catalytic pyrolysis in comparison with a N2 atmosphere, and a high liquid yield of more than 70% containing aromatic hydrocarbons, alkanes, and olefins was obtained with CO2 catalytic conversion to CO over a nickel-modified HZSM-5 catalyst. In addition, the total selectivity of aromatics was 56.82% with that of benzene, toluene, ethylbenzene, and xylene (BTEX) being 43.63% at 550 °C. Compared with untreated HZSM-5, the metal-modified HZSM-5 catalyst also enhanced anticoking performance during catalytic reactions with the assistance of active CO2 molecules. Besides, the involved catalytic reaction mechanism was also interpreted. The current work may offer a fresh route to the chemical recycling of waste plastics with simultaneous green CO2 reutilization, advancing the development of catalytic conversion of hydrogen-rich solid waste into value-added products.