Phase Segregation-Dictated superior Fe-rich ferrite composite for intensified methane dry reforming with CO2 splitting

• Composite structure boosts the oxygen transfer capacity and stability. • MgO promotes oxygen release from and deep reduction of Fe 3+ via oxygen spillover. • Phase segregation and reintegration enable sustained activity over cyclic reuse. • Promoted methane cracking reaction for an enhanced hydrogen production. • Promoted Boudouard reaction eliminates carbon despots for enhanced CO 2 splitting. Earth-abundant iron oxide serves as a promising oxygen carrier for the chemical looping dry reforming of methane, addressing the emission of both CH 4 and CO 2 . However, its development faces a challenge with a trade-off between high activity and stability. We successfully resolved this issue by advancing an Fe-rich (61 wt% Fe) oxygen carrier derived from a global waste, fly ash. This oxygen carrier incorporates six cations (Fe, Mg, Al, Ca, Ti and Mn) in a composite consisting of distorted spinel ferrites (MgFeAlO 4 and Fe 3 O 4 ) and discrete oxides (MgO and Fe 2 O 3 ), recording a superior oxygen transfer capacity of ∼ 19.8 mmol/g OC during the 900 °C CH 4 /CO 2 cycles. This is attributed to a promoted deep reduction of Fe 3+ , a high phase segregation of the structure due to oxygen migration, and a strong metal-support interaction between inert MgO and the deeply reduced metallic Fe 0 . Additionally, the oxygen carrier is capable of catalysing both CH 4 reforming and cracking reactions, yielding a high H 2 /CO molar ratio of 5.3 and a large H 2 production (∼70.6 mmol/g OC ) in the CH 4 reduction stage. In the subsequent CO 2 oxidation stage, the lattice oxygen is fully restored, and the Boudouard reaction is also catalysed by the trace cations (Ca, Ti and Mn) to eliminate the coke deposit effectively, which resulted in a total CO production of ∼ 82 mmol/g OC . Meanwhile, the segregated phases are re-integrated together, enabling a successful reversion of the structure for the oxygen carrier and its constantly high and stable activity over cyclic use.