Enhancement of highly-concentrated hydrogen productivity in chemical looping steam methane reforming using Fe-substituted LaCoO3

This work addresses chemical looping steam methane reforming (CL-SMR) for producing highly-concentrated hydrogen and syngas without any separation unit. The effect of transition metal substitution on the CL-SMR were investigated with LaCoO3 and B-site substituted LaCo0.6B0.4O3 (B = Fe, Mn, Ni). The cyclic CH4-H2O redox reaction revealed that Fe and Mn-substituted carriers maintained high steam regeneration, while LaCoO3 was not fully oxidized by steam. In particular, the Fe-substituted carrier provided the highest extent of steam regeneration, hydrogen purity and enhanced selective oxidation of CH4 to syngas, which was reflected in the 92% CO selectivity and 99.3% hydrogen purity with a produced amount of 2.22 mmol H-2/g(cat) at a relatively low temperature of 700 degrees C. H-2-TPR showed that the CO selectivity increased due to the lowering of the lattice oxygen transfer to the surface vacancies by the Fe substitution. In-situ XPS and O-2-TPD measurements revealed that the substitution enhances the adsorption and the decomposition of hydroxide ion on the surface and the oxygen mobility from the surface to the lattice, which facilitates steam splitting and the regeneration of lattice oxygen. LaCo0.6Fe0.4O3 was selected as the optimal oxygen carrier for the low-temperature CL-SMR process, which demonstrated the highest syngas selectivity and hydrogen purity with the enhanced cyclic stability.