Enhanced hydrogen production from polypropylene via NiO/Zeolite Y catalyzed high-pressure pyrolysis: Effects of pressure and methanation reactions

This study investigated the catalytic pyrolysis of polypropylene for hydrogen production using NiO-supported catalysts under varying pressure conditions. Experiments were conducted at 500–800 °C and 0.1–2 MPa. Thermogravimetric analysis revealed that moderate pressures delayed degradation owing to suppressed volatile release, whereas higher pressures accelerated thermal cracking and secondary reactions. Gas analysis indicated increased H₂ and CH₄ yields with increasing pressure, with CH₄ becoming dominant owing to favorable methanation. NiO/Al₂O₃ promoted hydrocarbon cracking but had a limited impact on CH₄ conversion. In contrast, NiO/Zeolite Y significantly improved the H₂ yield and suppressed CH₄ accumulation—particularly at 800 °C and 2 MPa. This was attributed to its large surface area and strong acidity, which enhanced reforming and reverse methanation. These findings highlight the combined influence of pressure and catalyst composition on the pyrolysis behavior and product distribution, offering insights for optimizing hydrogen-rich gas production from plastic waste.