Endogenous CO₂-assisted regeneration of biomass pyrolysis volatiles with dry reforming over NiFe₂O₄@SBA‑15

Endogenous CO₂ in biomass pyrolysis volatiles is commonly treated as a diluent, although it could potentially participate in oxygen-carrier regeneration and carbon reutilization. In this work, a coupled strategy integrating endogenous CO₂-assisted regeneration with chemical looping dry reforming of biomass pyrolysis volatiles was investigated. The objective was to determine whether endogenous CO₂ could be converted from a limiting component into a reactive carbon source under realistic reducing atmospheres containing CH₄, H₂, and CO. Thermodynamic analysis showed that methane dry reforming became favorable above 650 °C, while kinetic fitting indicated that the kinetic behavior over the reduced Ni_0.36Fe_0.64 phase was consistent with an MvK-type contribution with an E_a of 83.66 kJ·mol⁻¹. In situ DRIFTS and XRD results revealed that CO₂ activation proceeded through a hydrogen-assisted formate route and a direct carbonate route, and that the coexisting H₂/CO atmosphere suppressed surface oxidative reconstruction, shifting the active structure from a Ni-Fe₃O₄ interfacial state to a more reduced NiFe₃-rich alloy state. This structural evolution weakened CO₂ activation but favored syngas formation under strongly reducing conditions. At the process level, staged regeneration with endogenous CO₂ increases syngas production by 13.99% and achieves a lattice oxygen recovery rate of 45.75%. Light volatiles do not significantly increase syngas production, and the lattice oxygen recovery rate drops to about 20%; the H₂/CO in the volatiles has an inhibitory effect on oxygen carrier regeneration. The enhanced syngas production in Process 4 should be attributed to the combined effect of endogenous CO₂ utilization and exogenous biomethane-assisted DRM, increasing syngas yield by 34% and reduced CO₂ emissions by 10.5%. These results suggest that endogenous CO₂ can be repurposed as a reactive species for oxygen-carrier regeneration and syngas coproduction, providing a feasible route for improving carbon utilization and syngas production from biomass pyrolysis volatiles.