Lanthanide-controlled redox tuning in LnFeO3 perovskites for Low-COx hydrogen production via chemical looping methane decomposition

• A-site cation size governs reducibility and methane activation in LnFeO 3 perovskites. • LaFeO 3 delivers the highest Low-COx H 2 production among all tested perovskites. • Carbon forms as nanotubes, with a progressively higher graphitisation degree from La to Sm. • Smaller A-site cations hinder oxygen mobility, reducing methane decomposition activity. • All perovskites fully recover their structure over ten chemical looping cycles. This work presents a comparative study of LaFeO 3 , PrFeO 3 , NdFeO 3 , and SmFeO 3 perovskites as oxygen carriers for chemical looping methane decomposition (CLMD), aiming to produce hydrogen with no detectable COx formation within the limits of the analytical system. All these materials were synthesized by the self-combustion method, yielding similar crystal structures, surface areas, and sponge-like morphologies. Methane decomposition testing revealed a clear performance trend (La > Pr > Nd > Sm), which is correlated with the decreasing ionic radius of the A-site cation and its impact on reducibility, as confirmed by H 2 -temperature-programmed reduction (H 2 -TPR). LaFeO 3 achieved complete methane conversion and sustained hydrogen production across 10 CLMD cycles. Carbon deposits were predominantly in the form of nanotubes, as verified by SEM and Raman spectroscopy, with an increasing degree of graphitization from La to Sm, in agreement with TPO profiles. X-ray diffraction confirmed complete structural regeneration in all samples after cycling. These findings demonstrate that the A-site cation plays a decisive role in governing redox behavior, catalytic efficiency, and carbon nanostructure formation, providing a rational design pathway to optimize perovskite-based oxygen carriers in CLMD systems.