LaNixFe1-xO3-δ as a Robust Redox Catalyst for CO2 Splitting and Methane Partial Oxidation

The current study reports LaNi0.5Fe0.5O3-delta as a robust redox catalyst for CO2 splitting and methane partial oxidation at relatively low temperatures (similar to 700 degrees C) in the context of a hybrid redox process. Specifically, perovskite-structured LaNixFe1-xO3-delta (LNFs) with nine different compositions (x = 0.05-0.5) were prepared and investigated. Among the samples evaluated, LaNi0.4Fe0.6O3-delta and LaNi0.5Fe0.5O3-delta showed superior redox performance, with similar to 90% CO2 and methane conversions and >90% syngas selectivity. The standalone LNFs also demonstrated performance comparable to that of LNF promoted by mixed conductive Ce0.85Gd0.1Cu0.05O2-delta (CGCO). Long-term testing of LaNi0.5Fe0.5O3-delta indicated that the redox catalyst gradually loses its activity over repeated redox cycles, amounting to approximately 0.02% activity loss each cycle, averaged over 500 cycles. This gradual deactivation was found to be reversible by deep oxidation with air. Further characterizations indicated that the loss of activity resulted from a slow accumulation of iron carbide (Fe3C and Fe5C2) phases, which cannot be effectively removed during the CO2 splitting step. Reoxidation with air removed the carbide phases, increased the availability of Fe for the redox reactions via solid-state reactions with La2O3, and decreased the average crystallite size of La2O3. Reactivating the redox catalyst periodically, e.g., once every 40 cycles, was shown to be highly effective, as confirmed by operating the redox catalyst over 900 cumulative cycles while maintaining satisfactory redox performance.

Automated summary

LaNi0.5Fe0.5O3-δ exhibits excellent redox performance, showing high catalytic efficiency for CO2 splitting and methane partial oxidation. The gradual loss of activity can be addressed by deep oxidation with air, while periodic reactivation of the redox catalyst has been proven to effectively prolong its lifespan.