Tuning Chemical Looping Steam Reforming of Methane Performance via Ni-Fe-Al Interaction in Spinel Ferrites

The chemical looping steam reforming of methane (CLSR) employing Fe-containing oxygen carriers can produce syngas and hydrogen simultaneously. However, Fe-based oxygen carriers exhibit low CH4 activation ability and cyclic stability. In this work, oxygen carriers with fixed Fe content and different Fe/Ni ratios were synthesized by the sol–gel method to investigate the effects of Ni-Fe-Al interactions on CLSR performance. Ni-Fe-Al interactions promote the growth of the spinel structure and regulate both the catalytic sites and the available lattice oxygen, resulting in the CH4 conversion and CO selectivity being maintained at 96–98% and above 98% for the most promising oxygen carrier, with an Fe2O3 content of 20 wt% and Fe/Ni molar ratio of 10. The surface, phase, and particle size were kept the same over 90 cycles, leading to high stability. During the CLSR cycles, conversion from Fe3+ to Fe2+/Fe0 occurs, along with transformation between Ni2+ in NiAl2O4 and Ni0. Overall, the results demonstrate the feasibility of using spinel containing earth-abundant elements in CLSR and the importance of cooperation between oxygen release and CH4 activation.