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

Abstract

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 shows 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.