Synergetic promotional roles of CeO2 and Ni on red mud oxygen carrier for chemical looping steam methane reforming

Abstract

Red mud, an iron-containing industrial waste, has been explored as a potential oxygen carrier for chemical looping steam methane reforming (CL-SMR). However, its low reactivity requires enhancement. While Ni can improve the reactivity of red mud, the CH₄ conversion remains limited, which was less than 30% for red mud modified with 5 wt % NiO (5Ni-RM). In this work, the CeO₂–Ni co-doping red mud was developed for CL-SMR, and the synergetic effects of CeO₂ and Ni were investigated. Among the tested samples, red mud with 10 wt % CeO₂ and 5 wt % NiO loading (10Ce–5Ni-RM) exhibited the best performance. For 10Ce–5Ni-RM in 50 cycles, the average CH₄ conversion during steady-state operation was 67.6%, significantly higher than that of 5Ni-RM at 24.4%, and its CO selectivity was 83.6% with a H₂/CO ratio of 1.97. Furthermore, the syngas yield of 10Ce–5Ni-RM was 0.274 mmol g⁻¹·min⁻¹, 71.3% higher than that of 5Ni-RM, and its H₂ yield was 0.114 mmol g⁻¹·min⁻¹. The superior performance of 10Ce–5Ni-RM can be ascribed to the synergistic promotional roles of CeO₂ and Ni dopants. The interaction between these dopants and red mud generated CeO₂-based Ce–Ni–O and Ce–Fe–O solid solutions, as well as perovskite CeFeO₃, significantly promoting the generation of oxygen vacancies for lattice oxygen transfer. Besides, the metallic Ni activated CH₄ molecules, and the substitution of Ni²⁺ into Fe₃O₄ generated high-activity Ni–Fe–O spinel. Overall, the synergistic promotional roles of CeO₂ and Ni improved the reactivity and thus high gas yields for red mud oxygen carrier in CL-SMR.