Design of Ni-promoted Ca2Fe2O5/modified ceria as oxygen carrier for fast and carbon-resistant chemical-looping steam methane reforming

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Chemical looping steam methane reforming enables the production of high-purity syngas and hydrogen while eliminating the energy-intensive downstream separation steps typically required by conventional technologies. Ca 2 Fe 2 O 5 is a promising oxygen carrier thanks to its high redox stability and low equilibrium pO 2 . However, its practical application is hindered by sluggish reduction kinetics. Here, we have overcome this limitation by preparing nickel-promoted composite oxygen carriers (OC) through the physical mixing of Ca 2 Fe 2 O 5 and modified CeO 2 . The selective deposition of Ni on the surface of the CeO 2 -based phase significantly increases the OC reduction rate, outperforming samples in which Ni is in close contact with Ca 2 Fe 2 O 5 (either on the surface or within the lattice). SiO 2 modified ceria was found to be more effective than CeO 2 -Al 2 O 3 and Ce 0.8 Zr 0.2 O 2 in promoting the microstructural stability of CeO 2 within the composite, ensuring consistent performance over multiple redox cycles. The co-presence of Ca 2 Fe 2 O 5 and the catalyst in the same reactive bed effectively limits carbon formation at a low OC conversion degree. In situ synchrotron X-ray diffraction and isothermal packed-bed tests revealed a gas-mediated synergistic mechanism whereby carbon deposition was inhibited by H 2 O and CO 2 generated locally from the reduction of Ca 2 Fe 2 O 5 . This led to fast oxygen exchange and stable syngas production. After 50 reaction cycles, the composite OC produced 13.0 mmol/g of syngas in the reduction step with 88% CH 4 conversion, and 6.8 mmol/g of H 2 in the water splitting step with >99% purity, demonstrating the potential of this OC design strategy. (5×13 cm) • The simple mixing of Ca 2 Fe 2 O 5 and Ni/CeO 2 -SiO 2 yields active and stable OCs. • Ni spatially localized on CeO 2 -SiO 2 promotes Ca 2 Fe 2 O 5 reduction. • Gas phase mediated synergism among components is effective for carbon suppression. • Obtained high syngas/H₂ yield, stability over 50 cycles, and >99% H₂ purity.