Enabling Stable Chemical Looping CO2-Splitting with Strontium Ferrate-Spaced Structurally Reversible Strontium-Doped Iron Oxygen Carriers.

Chemical looping CO2-splitting has emerged as a promising carbon utilization technique for integration with large-scale centralized emission sources. Unlike chemical looping combustion, CO2-splitting is predominantly conducted using iron-based oxygen carriers (OCs) due to thermodynamic constraints. However, the phase transformation of iron/iron oxide often leads to severe sintering within a few cycles. To mitigate this issue, we incorporated alkaline earth metals (magnesium, calcium, and strontium) into iron oxide OCs. Among these, the strontium-incorporated iron oxygen carrier, prepared with molecular-level mixing, demonstrated superior dispersion and anti-sintering properties. It evolved into a mixture of strontium ferrate and strontium-doped iron oxide. The strontium ferrate particles became stable spacers that separated the strontium-doped iron oxide particles from severe sintering, allowing for reversible transitions between wustite (FeO) and magnetite (Fe3O4). Consequently, the Sr-modified OC sustained stable performance over 100 cycles of chemical looping CO2-splitting coupled with ethane cracking at 700 °C. In contrast, magnesium- and calcium-incorporated samples formed large single-phase oxide materials that were either inactive toward CO2-splitting or exhibited slow kinetics due to inhibited ion diffusion through the crystal lattice.