Oxygen radical-mediated process for synergistic H₂ production and CO₂ capture from sludge gasification

To overcome the low-H₂/high-CO₂ challenge in converting municipal sludge to clean syngas, a novel Fe/Ca-based oxygen carrier (FCOC) was produced using waste steel slag by Ca modification. At 730 °C, FCOC-assisted sludge gasification increased H₂ yield by 54.16 % and limited CO₂ to below 20 vol%, as in situ carbonation created a low-CO₂ atmosphere that thermodynamically favoured H₂ formation. Multi-level oxygen species were established, where adsorbed oxygen (O_ads) and bridge oxygen (O_bridge) accelerated initial conversion and lattice oxygen (O_lattice) maintained structural stability, while abundant •O₂^-/•O^- radicals opened low-barrier pathways for organics conversion. These features defined a critical "temperature switch" at 730 °C. In the synergistic zone (≤ 730 °C), CO₂ mineralization continuously drives hydrogen-forming reactions, whereas in the decoupling zone (> 730 °C), CaCO₃ decomposition triggers H₂-consuming reverse reactions. This work proposes a waste-derived oxygen-carrier strategy for hydrogen-rich syngas production and low-carbon valorization of municipal sludge and steel slag.