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, H2/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 H2/CO ratio was 2.01, and the most suitable temperature for CL-SMR was 900 °C. Furthermore, the H2 yield in steam oxidation stage was 2.20 mmol·g−1, and the H2 purity could be up to 99.86%. The Ni could effectively activate the CH bond of methane and facilitate the transfer of lattice oxygen, leading to high reactivity. It existed in the form of metallic Ni and FeNi alloy after methane reforming stage, and most of the Ni species would developed into the FeNi 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.