Ni-enhanced red mud oxygen carrier for chemical looping steam methane reforming

Red mud is an iron-contained industrial waste, and the feasibility for its application in chemical looping steam methane reforming (CL-SMR) was evaluated. The Ni-enhanced red mud was prepared, and the redox reactivity, CO selectivity, H-2/CO ratio, cyclic stability, and the resistance to carbon deposition and sintering were investigated. It was found that the Ni-enhanced red mud presented much higher reactivity than the unloaded one, and the red mud with NiO loading of 5 wt% (5NiO-RM) displayed the best performance with desirable reactivity and cyclic stability. For 5NiO-RM, the CO selectivity could reach 94.1%, the H-2/CO ratio was 2.01, and the most suitable temperature for CL-SMR was 900 C. Furthermore, the H-2 yield in steam oxidation stage was 2.20 mmol.g(-1), and the H-2 purity could be up to 99.86%. The Ni could effectively activate the C-H bond of methane and facilitate the transfer of lattice oxygen, leading to high reactivity. It existed in the form of metallic Ni and Fe-Ni alloy after methane reforming stage, and most of the Ni species would developed into the Fe-Ni spinel Ni0.4Fe2.6O4 in steam oxidation stage. Moreover, the impregnated NiO was beneficial to the particle porous structure, promoting the reactivity and redox stability.