Halite-structured (MgCoNiMnFe)O_x high entropy oxide (HEO) for chemical looping dry reforming of methane

The configurational disorder of high entropy oxides (HEOs) promotes the reversible exsolution–redissolution of constituent metal species. This unique feature could be exploited to facilitate cyclic lattice oxygen storage and exchange. Herein, we report an in situ generated, halite-structured (MgCoNiMnFe)O_x HEO, which simultaneously functions as a redox catalyst and an oxygen carrier for dry reforming of methane in a chemical looping process (CL–DRM). Accordingly, the (MgCoNiMnFe)O_x/ZrO₂ HEO catalyst exhibits outstanding DRM activity, syngas selectivity and cyclic stability compared to medium-entropy oxides and bimetallic oxides over 100 CL–DRM cycles at 800 °C. XRD analysis verified the entropy-mediated preservation of the alloy/HEO/ZrO₂ catalytic structure over CL–DRM cycles. XAFS studies revealed the reversible and cyclic evolution–dissolution of Ni, Fe, Co over redox cycles. The exsolved NiFeCo nanoalloy exhibited high efficiency in activating CH₄. This study has demonstrated the potential applications of HEO-based catalysts in efficient chemical looping processes.