(2026) Journal of Analytical and Applied Pyrolysis_Use of CO₂ for sustainable syngas production with controlled H₂/CO ratio during pyrolysis of waste tire

Lee S.; Lee T.; Lee J.; Lee M.S.; Kwon E.E.

(Elsevier B.V.) Journal of Analytical and Applied Pyrolysis ISSN: 1652370 Vol.200 Issue. Article No.108129 DOI: 10.1016/j.jaap.2026.108129

The increasing generation of waste tire rubber (WTR), reaching 1.5 billion units annually worldwide, poses environmental challenges due to its non-biodegradable nature. Nevertheless, conventional disposal methods such as landfilling, incineration, and recycling lead to the release of toxic chemicals. Thus, this study investigates CO₂-assisted catalytic pyrolysis using a 5 wt% Ni/Al₂O₃ catalyst to convert WTR into high-value syngas (H₂ + CO) while suppressing the formation of undesirable liquid pyrolysates. To compare between N₂ and CO₂ atmospheres, experiments were performed over the temperature range of 500–700 ˚C under each condition. The results demonstrate that introducing CO₂ as a reactive medium enhances syngas yield by promoting gas-phase reaction via partial oxidation of liquid pyrolysates. Under optimized conditions (700 ˚C under a CO₂ atmosphere), syngas production increased by 2.66-fold, particularly CO, compared to the reference state (N₂ atmosphere). In addition, the H₂/CO molar ratio of syngas could be controlled over a wide range (from 8.63 to 0.20) by adjusting CO₂ concentration (0–80 vol%) at 700 ˚C. This offers great potential for tailoring syngas composition in a single unit operation to meet the requirements of various applications, including Fischer-Tropsch process, methanol synthesis, etc. In addition, CO₂-assisted catalytic pyrolysis under 50 vol% CO₂ yielded 50.73 wt% of syngas (based on sample mass), confirming that the majority of the liquid pyrolysates had been decomposed. The present work provides a promising and sustainable strategy for simultaneous waste valorization and on-demand syngas composition control from end-of-life tires through the utilization of CO₂. © 2026 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

This work was supported by the National Research Foundation of Korea (NRF) grants funded by the Korean Government (MSIT) ( RS-2023-NR077231 ).