Oxygen release kinetics and mechanism study on Cu-, Co-, Mn-based oxygen carrier

Sol-gel derived CuO/CuAl₂O₄, Co₃O₄/CoAl₂O₄ and Mn₂O₃/Al₂O₃ oxygen carriers were studied in a fluidized bed reactor under CO₂ atmosphere, where the oxygen release characteristics under different temperatures were focused. The mechanism function and kinetics parameters in the oxygen release were obtained from the experimental data. In the process of oxygen release, the phases of CuO and CuAl₂O₄ performing as active components decompose to Cu₂O and CuAlO₂ with O₂ generation. While, only Co₃O₄ and Mn₂O₃ can release oxygen in Co₃O₄/CoAl₂O₄ and Mn₂O₃/Al₂O₃ oxygen carriers, in which Co₃O₄ and Mn₂O₃ are respectively reduced to CoO and Mn₃O₄; and CoAl₂O₄ and Al₂O₃ perform as inert carrier. The kinetic analysis show that the oxygen release of three oxygen carriers can be described by the nucleation and nuclei growth model. This means that after O₂ release the Cu-O bond (as an example) in the oxygen carrier is broken, generates Cu₂O active sites diffusing away from the reduction centers, and comes together to form Cu₂O clusters. The mechanism function G(x), the activation energy and the pre-exponential factor have different expressions or different values for different oxygen carriers. The activation energies in the oxygen release of CuO/CuAl₂O₄, Co₃O₄/CoAl₂O₄ and Mn₂O₃/Al₂O₃ oxygen carriers, are 226.37, 130.06 and 65.90 kJ/mol respectively; and the pre-exponential factors are 2.99×10⁶ s^-1, 4.96×10³ s^-1 and 27.37 s^-1 respectively.