(2026) Energy Conversion and Management_Toward a carbon-negative strategy for syngas production via CO₂-assisted catalytic pyrolysis of natural loofah residues

Kwon D.; Lee T.; Kwon E.E.

(Elsevier Ltd) Energy Conversion and Management ISSN: 1968904 Vol.365 Issue. Article No.121820 DOI: 10.1016/j.enconman.2026.121820

Pyrolysis is a promising technique for biomass valorization; however, its sustainability is constrained by its high energy requirements and associated CO₂ emissions. Here, CO₂ was employed as a reaction atmosphere for the Ni/Al₂O₃-catalyzed pyrolysis of natural loofah residues (NL) to enhance syngas production while enabling process-level carbon mitigation. Three reactor arrangements (conventional, in-line non-catalytic, and in-line catalytic) were compared to dissect the mechanistic function of CO₂. CO₂ became reactive at ≥ 490 °C, where it promoted the conversion of oxygenated volatile species into CO. This effect was further enhanced by Ni/Al₂O₃, increasing CO production from 54.25 mmol under N₂ to 96.14 mmol under CO₂, while decreasing the bio-oil fraction from 7.10 to 4.91 wt%. Reducing the heating rate to 5 °C min⁻¹ improved the overlap between NL devolatilization and CO₂ activation, resulting in a syngas selectivity of 98.54 %. The resulting biochar showed an equilibrium CO₂ uptake of 77.39 mg g⁻¹, comparable to that of post-activated biochars. Within the defined gate-to-gate system boundary, carbon accounting that included CO₂ utilization during catalytic pyrolysis and subsequent CO₂ uptake by the resulting biochar indicated a net CO₂ balance of −0.24 g CO₂ g⁻¹ NL. This carbon mitigation performance corresponds to an estimated benefit of 368.15 USD per ton of NL compared to conventional incineration. These results suggest that CO₂-assisted catalytic pyrolysis can be a viable strategy for converting biomass waste into syngas while contributing to circular carbon management. However, the carbon-negative implication should be interpreted within the defined system-boundary, as a full life-cycle assessment was beyond the scope of this study. © 2026 Elsevier Ltd.

This study was supported by the National Research Foundation of Korea (NRF) and was funded by the Korean Government (MSIT) (No. RS-2023-NR077231). Dohee Kwon also acknowledges the financial support from the Hyundai Motor Chung Mong-Koo Foundation.