Co-production of syngas and H2 from chemical looping steam reforming of methane over anti-coking CeO2/La0.9Sr0.1Fe1-xNixO3 composite oxides

Chemical looping steam reforming of methane (CL-SRM) is a novel process for the co-production of syngas and hydrogen without an additional purification process. However, the high activity of oxygen carriers is always accompanied by severe carbon deposition via the catalytic cracking of methane, which can result in the rapid deactivation of oxygen carriers and the production of low purity hydrogen. Herein, a series of novel composite oxide carriers of CeO2/La0.9Sr0.1Fe1-xNixO3 with varying doping ratios of Ni are developed to achieve selective and stable production of syngas and H-2. The redox performance of CeO2/La0.9Sr0.1Fe1-xNixO3 was evaluated in a fixed bed reactor coupling with various analytical methods. It is found that the Ni doping ratio of 0.2 can significantly enhance the performance and stability of CeO2/La0.9Sr0.1Fe1-xNixO3. It is speculated that the proper doping ratio of Ni can simultaneously improve the surface lattice oxygen vacancies and the lattice oxygen migration rate. The CH4 reforming over CeO2/La0.9Sr0.1Fe0.8Ni0.2O3 displays a very stable performance while avoiding obvious carbon deposition within 20 min, in which, the CH4 conversion, H-2 selectivity, and CO selectivity achieve 85%, 96%, and 88%, respectively. The yield of H-2 (>95% purity) reaches 23 mL/min in the subsequent steam oxidation of reduced CeO2/CeO2/La0.9Sr0.1Fe0.8Ni0.2O3. Its lattice oxygen can be completely recovered by the final air oxygenation. The CeO2/La0.9Sr0.1Fe0.8Ni0.2O3 exhibits high reactivity and stability in 10 redox cycles at 850 degrees C. These results demonstrate that the doping of Ni affords an efficient manner to regulate the lattice oxygen migration rate of perovskite oxides to match the surface reaction rate, thereby avoiding the deep reduction of surface metal ions within perovskite oxides and resulting carbon depositions during CL-SRM.