Spinel mixed oxides as oxygen carriers for chemical looping combustion

Several transition metal based mixed oxides with the spinel structure have been prepared, characterised and tested using a TGA apparatus simulating the oxidation and reduction periods in CLC. Despite the fact that gas phase diffusion limitations have been encountered under our TGA test conditions, the spinel materials were compared in terms of oxygen transfer capacity as well as oxidation and reduction rates. The best working spinel formulation is Cu0.95Fe1.05AlO4, with high oxygen transfer capacity, high oxidation rate, but a relatively low reduction rate compared to our reference formulation (60%NiO-40%NiAl2O4). Impregnating NiO on the former spinel material allowed to increase both oxygen transfer capacity and reactivity of the resulting materials. While oxidation rates in the same order of magnitude to that of the reference material could be obtained, the maximum measured reduction rate was still only slightly above half that of the reference material.