Unravelling the role of Co in mixed Ni-Co oxygen carriers/catalysts for H₂ production via sorption enhanced steam methane reforming coupled with chemical looping

Coupling steam methane reforming with calcium and chemical looping comprises an energy efficient pathway for intensified high-purity H₂ production. CaO carbonation enables the in-situ CO₂ removal, along with elevated CH₄ conversion and H₂ yield in a single step, while the energy demand of calcination is covered by the oxygen carrier oxidation. This work evaluated bimetallic Ni-Co oxygen carriers for their performance under the intensified reforming conditions, when applied as a mechanical mixture with a CaO-based material with a molar ratio of Ni-Co oxides to CaO of 0.5. In the reforming stage, the oxygen carrier underwent reduction to form a Ni-Co alloy, serving as catalyst for H₂ production with ∼94% purity and ∼90% yield at 650 °C. The subsequent oxidation of the Ni-Co oxygen carrier under air covered adiabatically ∼40% of the calcination energy demand, which is ∼42% higher compared to a monometallic Ni-based material. The better activity of Ni-Co materials was ascribed to Co, which enhances the oxidation kinetics, as confirmed via in-situ X-ray diffraction.