Double adjustment of Ni and Co in CeO2/La2Ni2-xCoxO6 double perovskite type oxygen carriers for chemical looping steam methane reforming

Abstract

Chemical looping steam methane reforming (CL-SMR) is a clean and efficient technology for the co-production of syngas and hydrogen. In this work, a series of Ni and Co doped CeO2/La2Ni2-xCoxO6 double perovskite composite oxygen carriers were developed. The introduction of Co increase a large number of surface active sites, which accelerates the surface activation of CH4, while the addition of Ni provides oxygen vacancies to promote the migration of lattice oxygen in the particles. The optimal substitution ratios of cobalt and nickel are 0.6 and 1.4, respectively. The CeO2/La2Ni1.4Co0.6O6 sample exhibits excellent syngas selectivity (95%) accompanied with high methane conversion (86%) in the methane reforming stage at 850℃, and close to 100% hydrogen concentrations in the steam oxidation stage. Density functional theory calculations demonstrated that the partial oxidation of methane is a strongly exothermic process, and the double perovskite loaded with CeO2 is more conducive to the activation of CH4 and prevents the generation of carbon deposition. The Ni-Co synergistic effect formed by the appropriate doping ratio of Ni and Co can also greatly promote the partial oxidation of methane. Subsequently, the deeply reduced metals combined with oxygen vacancies provide sufficient active stable points for water vapor cracking to generate high-purity hydrogen.