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 (Oads) and bridge oxygen (Obridge) accelerated initial conversion and lattice oxygen (Olattice) 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.