Interactions of Mg-Fe-Al-O oxygen carriers with rare earth dopants (Ce, Y, Sm, La, and Pr) in chemical looping steam reforming

Abstract

Chemical looping steam reforming (CLSR) is a novel process for syngas and hydrogen co-production. In this work, rare earth metals (Ce, Y, Sm, La, and Pr) were doped to improve the reactivity and cyclic stability of the Fe-based oxygen carrier for CLSR. The cyclic tests indicate that the oxygen carrier doped with rare earth possesses a higher CH4 conversion rate, oxygen transport capacity, and hydrogen selectivity and yield. The crystal structure, surface morphology, and reactivity of the oxygen carrier were characterized by different analytical methods (e.g., XRD, H2-TPR, XPS, and SEM). The rare earth-doped oxygen carrier shows higher active site dispersion and smaller crystallite size owing to stronger metal-support interactions between the metallic Fe and the rare earth. XRD and SEM results revealed that the introduction of rare earth increases the oxygen transport capacity and oxygen vacancy concentration, promoting the reactivity of oxygen carriers. However, the rare earth doping reduces the CO purity, possibly because the high reactivity favors full CH4 oxidation. Among the prepared oxygen carriers, Fe10La exhibited the best performance and stability over cycles, with a high CH4 conversion rate (89.2%) and hydrogen purity (95 vol%).