Reaction characteristics of La/Co doped Mg-Fe-Al-O spinel oxygen carriers for chemical looping steam methane reforming

Abstract

Chemical looping steam methane reforming (CLSMR) is an efficient and promising method to co-produce syngas and hydrogen. In this work, the La/Co doped Mg-Fe-Al-O spinel was synthesized via co-precipitation method as oxygen carrier in CLSMR. The introduction of La ions enhances the dispersion of the iron oxide on the particle surface and retards the growth of the oxygen carrier grain size, and the incorporation Co ions creates oxygen vacancies, which facilitates the lattice oxygen migration. The results reveal the optimal ratios of La: Co is 5:5 in the doping. In the reduction, the La5Co5 sample generates the syngas with a H₂/CO molar ratio of ∼2, a CH₄ conversion rate of 85.1 %, and a syngas yield of 3.75 mmol/g_oc. In the oxidation, H₂ is produced with a yield of 1.25 mmol/g_oc and a concentration > 95 vol%. In SEM and XRD characterization analysis, the La5Co5 oxygen carrier after multiple reaction cycles exhibits minimal sintering, with stable phases and slight changes in grain size. The LaCo synergistic effect can also enhance the methane partial oxidation. The deep-reduced oxygen carrier owns sufficient oxygen vacancies as active sites for steam splitting to produce high concentration hydrogen.